GRAPHENE-BASED NANOSENSOR FOR IDENTIFYING TARGET ANALYTES
A microdevice for monitoring a target analyte is provided. The microdevice can include a field effect transistor comprising a substrate, a gate electrode, and a microfluidic channel including graphene. The microfluidic channel can be formed between drain electrodes and source electrodes on the substrate. The microdevice can also include at least one aptamer functionalized on a surface of the graphene. The at least one aptamer can be adapted for binding to the target analyte. Binding of the target analyte to the at least one aptamer can alter the conductance of the graphene.
This application is a continuation in part of U.S. Non-Provisional application Ser. No. 15/374,375, filed Dec. 9, 2016, which claims priority from International Application No. PCT/US15/035640, filed Jan. 12, 2015, which claims priority from U.S. Provisional Application No. 62/011,481, filed Jun. 12, 2014, Provisional Application No. 62/100,366, filed Jan. 6, 2015, and Provisional Application No. 62/100,379, filed Jan. 6, 2015, each of which is incorporated by reference herein in its entirety, and priority to each of which is claimed.
This application is a continuation in part of U.S. Non-Provisional application Ser. No. 15/374,375, filed Dec. 9, 2016, which also claims priority from International Application No. PCT/US16/012297, filed Jan. 6, 2016, which claims priority from U.S. Provisional Application No. 62/100,412, filed Jan. 6, 2015, each of which is incorporated by reference herein in its entirety, and priority to each of which is claimed.
This application is a continuation in part of U.S. Non-Provisional application Ser. No. 15/374,375, filed Dec. 9, 2016, which also claims priority from International Application No. PCT/US16/037362, filed Jun. 14, 2016, which claims priority to U.S. Provisional Application Ser. No. 62/180,484, filed on Jun. 16, 2015, and U.S. Provisional Application Ser. No. 62/188,281, filed on Jul. 2, 2015, each of which is hereby incorporated by reference in its entirety, and priority to each of which is claimed.
This application claims priority to U.S. Provisional Application Ser. No. 62/523,516, filed on Jun. 22, 2017, which is incorporated by reference herein in its entirety.
STATEMENT REGARDING FEDERALLY FUNDED RESEARCHThis invention was made with government support under 1DP3 DK101085 awarded by the National Institutes of Health and under ECCS-1509760 awarded by National Science Foundation. The government has certain rights in this invention.
BACKGROUNDSeveral hundred million people in the world have diabetes, making it a leading cause of death. In addition, complications induced by diabetes, such as heart disease, stroke, hypertension, blindness, kidney failure, and amputation, impact many others. Tight control of glycemia can reduce certain diabetes-related complications by 50% or more among Type I diabetics, with similar results for Type II diabetes patients. Thus, it is important to closely monitor abnormal blood sugar levels in diabetes patients so timely treatments (e.g., insulin injection, exercise, and diabetic diet, intake of carbohydrates) can be administered.
Certain glucometers with sparsely discrete measurements, however, do not allow tight blood sugar control. In contrast, continuous glucose monitoring (CGM) can effectively detect hypo- and hyperglycemic (i.e., low and high blood sugar, respectively) events. CGM can achieve this by taking repetitive measurements of physiological glucose concentrations to enable close monitoring and timely correction of problematic blood sugar patterns of patients with diabetes mellitus. CGM can reduce the risk of diabetes-related complications, but certain CGM devices are not adequate because of limited stability, insufficient accuracy, and slow time.
CGM can be achieved via minimally invasive or noninvasive methods, such as those which use subcutaneously implanted devices that determine glucose concentration in interstitial fluid (ISF) via measurement of electrochemical enzymatic reactions or equilibrium-based affinity binding. Electrochemistry, however, can involve irreversible consumption of glucose and depends on the rate at which glucose reaches the electrodes, which often makes electrochemical CGM sensors susceptible to influences of reactant supply rates, electroactive interferences, and biofouling (deposition of biological material such as proteins and cell debris on sensor surfaces). As a result, certain sensors can exhibit drifts, have delays, require frequent calibration, and have limited accuracy (especially at low glucose concentrations), not have adequate accuracy in the hypoglycemic realm (blood glucose concentration below 70 mg/dL), and exhibit significant delays.
Nonreactive methods that use equilibrium affinity binding of glucose to a specific receptor and do not involve irreversible consumption of glucose and can offer improved stability. Affinity glucose sensing can use concanavalin A (Con A), a glucose-binding protein, which unfortunately lacks stability and whose toxicity generates safety concerns.
Glucose sensors using stable, nontoxic glucose-binding can be limited by issues in accuracy, time response or miniaturization. Micro/nanoscale glucose affinity sensors, using microelectromechanical systems (MEMS), as well as using nanoscale materials such as carbon nanotubes, offer improvement in accuracy and stability, but can suffer from slow time response, rigid construction, and poor sensitivity. Moreover, they can be invasive by requiring subcutaneous implantation.
Noninvasive devices can attempt detection of interstitial fluid (ISF) glucose across the skin use optical spectroscopy or transdermal ISF sampling, which can be susceptible to variations in skin conditions. Others can use a measurement of glucose in urine, saliva, and tears. Unfortunately, glucose concentration in urine does not necessarily accurately reflect that in plasma, in particular in the hypoglycemic regime. Electrochemical methods to detect saliva glucose levels can suffer from the presences of residual food in saliva which can cause interferences.
Certain correlations have been found between tear and blood glucose concentrations, with deviations attributable to artifacts such as inconsistent tear collection methods. For example, the absorption and emission spectra of boronic acid containing fluorophores for glucose sensing can cumbersome and prevent CGM. Contact lens-based electrochemical sensors using glucose oxidase can be error-prone because of the irreversible nature of the reaction which consumes glucose during the measurement process.
There is a need to develop noninvasive glucose monitoring systems that offer improved long-term accuracy and stability, biocompatibility, resistance to biofouling, resistance to environmental parameter fluctuations, easier calibration, as well as the capability of providing real-time report of a subject's glucose level via wireless telemetry.
Certain approaches to blood-based glucose monitoring can involve extracting blood such as by intermittent finger-stick testing, or continuous glucose monitoring, and can have drawbacks. For example, apart from the invasive and sometime painful extraction of blood, finger-stick glucose monitoring can miss abnormal blood excursions. Continuous glucose monitoring, while able to monitor glucose levels throughout the day via electrochemical detection, can suffer from interferences from electroactive chemicals. MEMS (micro-electro-mechanical systems) technology can enable innovative subcutaneously implanted sensors to measure concentrations of certain molecules, such as glucose, in interstitial fluid (ISF). Such sensors can employ affinity binding between the target molecules and a sensing material to achieve high accuracy and stability.
Affinity sensors based on dielectric measurements can be used in applications such as detecting or quantifying biochemical targets under excitations at various frequencies. However, such microsensors utilizing dielectric measurements can lack sufficient sensitivity for the detection of certain low-charged and low-molecular-weight molecules. Additionally, MEMS devices can be limited by complicated and inefficient designs or slow time responses. For example, affinity glucose sensing has been implemented using optical, mechanical, and electrical methods on conventional or microscale platforms typically requiring complex sensor structures such as moving mechanical components or physical barriers. Semi-permeable membranes or other physical barriers or mechanically movable structures can increase complexity of the devices and limit the reliability of the devices.
Graphene is a single a single atom thick two-dimensional nanomaterial with honeycomb lattice of carbon. While graphene can be attractive functional nanomaterial in sensors that allow highly sensitive detection of chemical and biological analytes, analytes and like molecules detectable by such graphene-based sensors can be highly charged or strong electron donors or acceptors that can induce carrier doping in graphene for field effect transistor (FET)-based measurements. Graphene can form a conducting channel in field effect transistors (FETs), allowing sensitive electrically based detection of gas molecules, physiological parameters of liquids (e.g., pH level) and biological molecules (e.g., proteins) in solution. Glucose, however, is an uncharged, low-molecular-weight molecule. Sensitive detection of glucose has been accomplished within graphene FET—based enzymatic sensors. Unfortunately, due to the irreversible, consumptive nature of the enzyme-catalyzed electrochemical reactions of glucose, as well as undesirable byproducts (e.g., hydrogen peroxide) generated in the reactions of enzymes and glucose, certain enzyme-based sensors can suffer from limitations in stability and accuracy when operating in physiological environments.
Subcutaneous detection of certain low-charged molecules, low-molecular weight molecules, which can be important for applications such as glucose monitoring, thus still remains a challenge. Accordingly, a need exists for an accurate, subcutaneous sensor reliable for continuous monitoring of low-charged molecules in a physiological environment.
Furthermore, although graphene nanosensors configured as FETs can provide a sensitive, label-free biomarker detection platform because of the ability of surface-based binding to cause changes in the bulk properties of graphene, certain existing aptameric graphene nanosensors have been limited to well-conditioned buffers, while analyte detection in physiological samples such as human serum has remained a challenge. One difficulty involves the hydrophobic nature of pristine graphene, as background molecules in serum tend to nonspecifically adsorb to the graphene surface, thus interfering with the detection of the target analyte. Another difficulty is their application to the detection of small biomolecules is still limited, as the binding of low charged small molecules does not directly induce detectable changes in graphene conductance, hence suffering low sensitivity.
Furthermore, understanding binding properties of biomolecules and their dependence on environmental conditions such as temperature and ionic strength can be of great interest to basic science studies and applied pharmacology. While successful characterization of biomolecular binding properties can be performed with traditional methods (e.g., optical, electrochemical, and electromechanical characterization), the traditional approaches for binding studies commonly either require molecular labeling groups and/or involve complex sensor structure and instrumentation.
There is a need to develop graphene nanosensors that offer improved specificity and sensitivity, including for diagnostic testing. Furthermore, there is a need for nanosensors that can be used to characterize biomolecular interactions under different levels of ionic strength and temperature.
SUMMARYThe disclosed subject matter provides microdevices and techniques for monitoring a target analyte.
In one aspect, the disclosed subject matter provides a microdevice and techniques for monitoring a target analyte in a sample using a receptor capable of binding to the target analyte. In one aspect, the microdevice does not require a receptor that binds the target analyte.
In certain embodiments, a microdevice includes a nanosensor, on a substrate platform, including a pair of conductance sensors functionalized with a receptor. One receptor (sensing receptor) binds specifically to the target analyte, and the other (reference receptor) is insensitive to the target analyte. Target analyte binding of the sensing receptor changes the charge density on the sensor surface, inducing changes in the carrier concentration of the sensor. Meanwhile, the reference receptor does not bind to the target analyte and its associated sensor conductance would change due to fluctuations in environmental parameters. Thus, differential measurement of the target analyte conductance allows determination of the target analyte concentration in, for example, a sample or bodily fluid. In certain embodiments, the receptors bind reversibly with essentially all analytes. In certain embodiments, the sensing receptor binds reversibly with the target analyte. In certain embodiments, the receptor is a synthetic polymer. In certain embodiments, the sensor includes graphene.
In certain embodiments, a microdevice includes a nanosensor, on a substrate platform, including a single conductance sensor functionalized with synthetic receptors (sensing receptors), which bind specifically to the target analyte, on a substrate platform. Target analyte binding of the sensing receptor changes the charge density on the sensor surface, inducing changes in the carrier concentration of the sensor allowing for the determination of the target analyte concentration in, for example, a sample or bodily fluid. In certain embodiments, the sensing receptor binds reversibly with the target analyte. In certain embodiments, the receptor is a synthetic polymer. In certain embodiments, the sensor includes graphene.
The disclosed subject matter also provides microdevices for monitoring a target analyte in a bodily fluid using a polymer capable of binding to the target analyte. In certain embodiments, the microdevice includes a substrate platform and a nanosensor including a first conductance element functionalized with a sensing polymer for detecting the target analyte and a second conductance element functionalized with a reference polymer that is insensitive to the target analyte. Detecting a difference, if any, in the conductance of the first and second conductance elements can be used to determine the presence and/or concentration of the target analyte in the sample. In some embodiments, the differential measurement of the conductance of the first and second conductance elements can reject or minimize environmental effects on the disclosed microdevices. In non-limiting embodiments, the target analyte can be at physiologically relevant concentration in the sample.
In certain embodiments, the microdevice includes a graphene nanosensor on a contact lens platform. A noninvasive contact lens-based nanosensor, which is miniaturized and mechanically flexible, can include graphene functionalized with a glucose-binding polymer and enable noninvasive CGM. By differential measurement of glucose binding-induced changes in graphene conductance as compared to measurements from a sensor insensitive to glucose, the device can allow specific, sensitive, and rapid detection of glucose concentration in tear fluid. In certain embodiments, the nanosensor includes a pair of graphene conductance sensors on a flexible, contact lens-based substrate respectively functionalized with synthetic polymers. In certain embodiments, synthetic glucose-specific polymers and reference polymers can be grafted on graphene surfaces for differential measurements. In certain embodiments, the polymer includes a PAAPBA based polymer. In certain embodiments, the polymer includes a plurality of boronic acid moieties.
In certain embodiments, the nanosensor can be coated with a biocompatible glucose-permeable hydrogel thin layer. Glucose binding of the sensing polymer changes the charge density on the graphene surface, inducing changes in the carrier concentration within the bulk of the atomically thin graphene and hence in the graphene electric conductance.
In certain embodiments, the microdevice can be adapted to be disposed on or coupled to a contact lens-based substrate, a dermal patch, an eye patch, a tattoo, jewelry, a watch, bandages, clothing, or a wireless body sensor.
In certain embodiments, the bodily fluid is tears, blood, saliva, mucus, interstitial fluid, spinal fluid, intestinal fluid, amniotic fluid, lymphatic fluid, pericardial fluid, peritoneal fluid, pleural fluid, semen, vaginal secretions, sweat, or synovial fluid of a subject.
The disclosed subject matter also provides synthetic polymer-functionalized affinity-based nanosensors for detection of low-charge, low-molecular-weight molecules, such as, for example and without limitation, glucose. The disclosed subject matter can utilize a material functionalized with a synthetic polymer monolayer derivatized with a boronic acid group whose reversible complexation with the target low-charge, low-molecular-weight molecule (e.g., glucose) generates a detectable signal.
In one aspect of the disclosed subject matter, a graphene-based affinity nanosensor is provided. The binding of the polymer monolayer with glucose on the graphene surface of the device can induce changes in the carrier density and mobility in the graphene, which can cause an increase in charge on the graphene. Thus, the binding can offer a high detection sensitivity of the target molecule and/or analyte.
For example and without limitation, an affinity nanosensor for detection of low-charge, low-molecular-weight molecules includes a solution-gated field effect transistor, which can enable reliable monitoring of a target molecules in a sample solution. The solution-gated field effect transistor can include a silicon substrate, a source electrode disposed on the silicon substrate, and a drain electrode disposed on the silicon substrate. The graphene can be a graphene sheet, which can be disposed between the source electrode and drain electrode and can connect the source and drain electrodes. The solution-gated field effect transistor can further include graphene functionalized with a synthetic polymer monolayer, which is disposed between the source electrode and drain electrode on the silicon substrate. The functionalized graphene forming a conducting channel of the solution-gated field effect transistor, and the synthetic polymer monolayer being responsive to a first analyte. The affinity nanosensor can also include a reference electrode disposed between the source and drain electrodes, and an electrical double layer at the interface of the graphene and solution comprising a gate capacitor.
Additionally, or alternatively, the silicon substrate can be an oxidized silicon substrate wafer. The source electrode and drain electrode can be gold electrodes. The synthetic polymer monomer can include a boronic acid. The graphene can be functionalized with the synthetic polymer monolayer via π-π stacking interactions. The first analyte can be glucose. The reference electrode can include silver chloride. Furthermore, the gate capacitor can be affected by varying concentrations of the first analyte in the sample solution.
The graphene-based affinity nanosensor can include any or all of the features described herein.
According to another aspect of the disclosed subject matter, methods of fabricating an affinity nanosensor for detecting low-charge, low-molecular-weight molecules are provided. An example method includes providing a silicon substrate wafer having a uniform thickness throughout, the wafer having oppositely disposed top and bottom faces; and providing a first gold portion on the top face of the first material, and a second gold portion separated from the first gold portion by a channel region. The method can further include transferring graphene onto the top face of the wafer in the channel region to connect the first and second gold portions, and functionalizing the graphene with a synthetic polymer monolayer, the synthetic polymer monolayer being sensitive to a first analyte. The method can also include mounting a conductive wire within the channel region.
Additionally, or alternatively, the providing the first and second gold portions can include etching the first gold portion and the second gold portion to the top face of the wafer. The transferring the graphene can include coupling graphene to the top face of the wafer via chemical vapor deposition. Furthermore, the functionalizing can include immersing at least the graphene transferred onto the wafer in a solution comprising boronic acid for at least four hours at room temperature, and washing the graphene transferred onto the wafer using methanol. The immersing can include coupling a pyrene-1-boronic acid to the graphene via π-π stacking interactions. The mounting the conductive wire within the channel region can include providing a silver wire mounted on a positioner to serve as a gate electrode.
In another aspect of the disclosed subject matter, hydrogel-based affinity nanosensors are provided. For example, an affinity nanosensor can include a parallel plate transducer, a synthetic hydrogel disposed between a first plate and a second plate of the parallel plate transducer, the hydrogel being responsive to a first analyte, and a temperature sensor located below the first and second plates.
Additionally, or alternatively, the first and second plates of the parallel plate transducer each further include a sensing electrode. The sensing electrode can be formed of gold. At least one of the first plate and second plate of the parallel plate transducer can be perforated and passivated within a perforated diaphragm. The at least one perforated plate and at least one perforated diaphragm can be supported by at least one micropost. The synthetic hydrogel of the affinity nanosensor can further include a synthetic copolymer including boronic acid. The first analyte can be glucose.
The hydrogel-based affinity nanosensor can include any or all of the features described herein.
According to yet aspect of the disclosed subject matter, an example method for fabricating an affinity nanosensor for detecting low-charge, low-molecular-weight molecules includes providing a silicon substrate wafer having a uniform thickness throughout and having oppositely disposed top and bottom faces, providing a first electrode on the top face of the wafer, and providing a second electrode, spaced a first distance over the first electrode, above the top face of the wafer, the second electrode being supported above the top face of the wafer by at least one micropost. The method can also include preparing a hydrogel functionalized with a polymer responsive to a first analyte and filling the hydrogel between the first and second electrodes.
The method can also include providing the second electrode with one or more perforations and separating the second electrode from the hydrogel by a perforated diaphragm. The first analyte can be glucose. Furthermore, the preparing the functionalized hydrogel can include synthesizing the hydrogel in situ via polymerization of the hydrogel with a boronic acid, and gelating the hydrogel between the first and second electrodes.
As herein disclosed, a sample solution containing such low-charge, low molecular-weight molecules can be a bodily fluid, a non-bodily fluid, or a laboratory sample. The bodily fluid can be, for example and without limitation, tears, blood, saliva, mucus, ISF (interstitial fluid), amniotic fluid, lymphatic fluid, pericardial fluid, peritoneal fluid, pleural fluid, sweat, or other bodily fluid of a subject.
The disclosed subject matter further provides systems and methods for detecting small biomolecules using a microfluidic nanosensors including a graphene nanosensor. The disclosed subject matter also provides a microdevice and techniques for monitoring a target analyte. In one aspect, the disclosed subject matter provides a microdevice and techniques for monitoring a target analyte in a sample using an aptamer capable of binding to the target analyte.
In certain embodiments, a microdevice includes a graphene nanosensor, on a substrate platform, wherein the graphene nanosensor can be functionalized with an aptamer that binds the target analyte. Target analyte binding of the aptamer changes the charge density on the graphene nanosensor surface, inducing changes in the carrier concentration of the sensor. In certain embodiments, the aptamers bind reversibly with essentially all analytes. In certain embodiments, the aptamers bind reversibly with the target analyte. In some embodiments, the aptamers can include insulin specific aptamers. For example, the insulin specific aptamers can include guanine-rich IGA3 aptamers.
The nanosensor can have a FET configuration. In accordance with an exemplary embodiment, the nanosensor can include a substrate. The substrate can be, for example, a SiO2-coated silicon wafer. Source and drain electrodes can be patterned on the substrate. A graphene sheet can be coupled to the source and drain electrodes. The graphene surface can be functionalized with aptamers that binds the target analyte. A polymeric material (e.g., PDMS sheet) can define the well for testing the sample.
The disclosed subject matter also provides a microfluidic aptasensor including an enrichment chamber and a sensing chamber. The enrichment chamber can include one or more microbeads. Aptamers can be immobilized on the surface of the microbeads.
The sensing chamber can include a graphene nanosensor. The nanosensor can have a FET configuration. In accordance with an exemplary embodiment, the nanosensor can include a substrate. The substrate can be, for example, a SiO2-coated silicon wafer. Gate electrodes can be patterned on the substrate. A single-layer graphene sheet can connect the source and drain electrodes. The graphene surface can be functionalized with a control target analyte. A polymeric material (e.g., PDMS sheet) can define microchambers and channels.
The enrichment chamber and the sensing chamber can be coupled via a serpentine channel. In accordance with embodiments of the disclosed subject matter, the aptasensor can further include a temperature control unit, an inlet coupled to the enrichment chamber, a waste outlet coupled to the serpentine channel, and a sample outlet coupled to the sensing chamber.
In accordance with another embodiment, the disclosed subject matter provides methods for detecting small biomolecules using a microfluidic graphene nanosensor. A sample can be introduced into the polymeric well. Target analytes (e.g., IgE) can be selectively captured by aptamers immobilized on the graphene nanosensor. Non-target molecules, including impurities, can then be removed through, e.g., buffer washing. The electrical conductance through the change in conductance caused by the target analyte binding to the aptamer immobilized on the graphene can be measured by measuring the drain current at a fixed drain voltage.
In accordance with yet another embodiment, the disclosed subject matter provides methods for detecting small biomolecules using a microfluidic aptasensor including an enrichment chamber and a sensing chamber. A sample can be introduced into the enrichment chamber. Target analytes (e.g., AVP) can be selectively captured by aptamers immobilized on microbead surfaces. Non-target molecules, including impurities, can then be removed through, e.g., buffer washing. The enriched target molecules can then be released at an elevated temperature and eluted with free aptamer. This mixture can travel to the sensing chamber via a serpentine channel. The eluate can be incubated with graphene pre-functionalized with a control (e.g., reagent) target analyte (e.g., with reagent AVP). The graphene-bound control (e.g., reagent) target analyte can compete with the sample target molecules to bind to and capture some of the free aptamer molecules, which can cause an increase in charge on the graphene. The electrical conductance through the graphene can be measured by measuring the drain current at a fixed drain voltage.
In one aspect, the aptamer can be a single-stranded oligonucleotide or a peptide. In certain embodiments, the aptamer can be a single-stranded oligonucleotide, which can be DNA, RNA, XNA, or a combination thereof. In certain embodiments, the aptamer can be functionalized to the surface of graphene via a linker. The linker can be a pyrene-terminated agent (e.g., 1-pyrenebutanoic acid succinimidyl ester). In certain embodiments, the graphene can be serially functionalized with a polymer (e.g., polyethlene glycol) and aptamers. In accordance with certain embodiments, the polymer can be coupled to the aptamer and the opposite end of the polymer can be coupled to the linker.
In certain embodiments, the nanosensor as disclosed herein can enable reliable monitoring of a target analyte in a sample. In certain embodiments, the sample can be a bodily fluid, a non-bodily fluid liquid, or a laboratory sample. In certain embodiments, the nanosensor can be used to measure the amount or change in the amount of a target analyte in a sample. In certain embodiments, the bodily fluid can be tears, blood, saliva, mucus, interstitial fluid, spinal fluid, intestinal fluid, amniotic fluid, lymphatic fluid, pericardial fluid, peritoneal fluid, pleural fluid, semen, vaginal secretions, sweat, or synovial fluid of a subject. In non-limiting embodiments, the nanosensor can perform real-time detection of a target analyte concentration.
In accordance with yet another embodiment, the disclosed subject matter provides a microdevice for monitoring a target analyte. The microdevice can include a field effect transistor comprising a substrate, a gate electrode, and a microfluidic channel including graphene. The microfluidic channel can be formed between drain electrodes and source electrodes on the substrate. The microdevice can also include at least one aptamer functionalized on a surface of the graphene. The at least one aptamer can be adapted for binding to the target analyte. Binding of the target analyte to the at least one aptamer can alter the conductance of the graphene.
In certain embodiments, the microfluidic channel can be bound to the substrate for analyte and buffer introduction to initiate association and dissociation of the target analyte to the at least one aptamer.
In certain embodiments, the field effect transistor can include a gate capacitor comprising of an electrical double layer formed at the interface of the graphene and the solution.
In certain embodiments, binding of the target analyte to the at least one aptamer can cause a conformational change of the at least one aptamer, causing the target analyte to be brought into a proximity to the surface of the graphene. The target analyte being brought into proximity to the surface of the graphene can cause electrical properties of graphene to change by at least one of charge transfer and electrostatic interaction. In some embodiments, the conformational change can include parallel G-quadruplex conformation and/or antiparallel G-quadruplex conformation.
In certain embodiments, the microdevice can include at least one of an on-chip temperature sensor and a Peltier module to perform closed-looped temperature control of the microdevice.
In certain embodiments, the microdevice can be configured to provide a label-free direct characterization of biomolecular binding properties with one-step electrical readout.
In certain embodiments, binding of the target analyte to the aptamer can cause a carrier concentration in the graphene to be altered, resulting in a detectable signal.
In certain embodiments, the at least one aptamer can be functionalized on the surface of the graphene using a linker. The linker can be configured to be irreversibly attached to the graphene without altering electronic properties of the graphene. In certain embodiments, the at least one aptamer can be directly attached to the linker by forming an amide bond. The linker can be coupled to the graphene via stacking. The at least one aptamer can be attached to the free end of linker by forming an amide bond. In certain embodiments, the linker can include 1-pyrenebutanoic acid succinimidyl ester (PASE). In some embodiments, aptamers can be coupled to PASE through a reaction of an amino group of the aptamer with N-hydroxysuccinimide ester of PASE.
In certain embodiments, the field effect transistor can include a source electrode and a drain electrode. The graphene can make contact with both the source electrode and the drain electrode. In certain embodiments, the graphene can be a single layer sheet.
In certain embodiments, the target analyte can be disassociated from the at least one aptamer by introducing a buffer to the at least one aptamer.
In accordance with yet another embodiment, the disclosed subject matter provides for a method for monitoring a target analyte using an aptamer capable of binding to the target analyte. The method can include placing a nanosensor in contact with target analytes such that the nanosensor includes a first conductance element functionalized with an aptamer configured to detect the target analyte and a second conductance element that is insensitive to the target analyte. The method can include detecting a difference, if any, in the conductance of the first and second conductance elements. The method can include determining, based on the detected difference, a presence of the target analyte. In some embodiments, the method can further include modifying the aptamer to adjust a specificity of the nanosensor to the target analyte.
In certain embodiments, the binding of the aptamer with the target analyte can causes a change in the charge density on the first conductive element surface.
In certain embodiments, the disclosed microdevice and/or nanosensor can detect changes in the target analyte concentration in real-time. In some embodiments, the detection can be continuous over time
In certain embodiments, a differential measurement of the conductance of the first conductance element and the second conductive element can provides for determination of the presence of the target analyte. In some embodiments, the target analyte can include an insulin molecule.
In certain embodiments, the first conductive element can include a surface adapted for a change in charge density thereon upon the binding of the aptamer with the target analyte.
The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the disclosed subject matter. Together with the description, the drawings serve to explain the principles of the disclosed subject matter.
Further features and advantages of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the present disclosure, in which:
The disclosed subject matter provides for devices and techniques to monitor target analytes. More specifically, the disclosed subject matter provides for field-effect transistor (FET)-based sensors and systems that can be used for continuous analyte monitoring, including but not limited to continuous glucose monitoring (CGM).
As used herein, the term “analyte” is a broad term and is used in its ordinary sense and includes, without limitation, any chemical species the presence or concentration of which is sought in material sample by the sensors and systems disclosed herein. For example, the analyte(s) include, but not are limited to, glucose, ethanol, insulin, water, carbon dioxide, blood oxygen, cholesterol, bilirubin, ketones, fatty acids, lipoproteins, albumin, urea, creatinine, white blood cells, red blood cells, hemoglobin, oxygenated hemoglobin, carboxyhemoglobin, organic molecules, inorganic molecules, pharmaceuticals, cytochrome, various proteins and chromophores, microcalcifications, ions, electrolytes, sodium, potassium, chloride, bicarbonate, and hormones. In one embodiment, the analyte can be glucose. In various embodiments, the analytes can be other metabolites, such as lactate, fatty acids, cysteines and homocysteines.
As used herein, the term “functionalized” means to have a capability of being reactive to an analyte. For example, functionalized refers to a substrate that has a substance attached, conjugated, or grafted to it, wherein the substance has a functional group that is capable of reacting with an analyte. For example, the substance can be covalently attached, conjugated, or grafted to the surface of the functionalized substrate.
As used herein, the terms “device,” “sensor,” and “nanosensor” are interchangeable and used here as a reference to low-charge, low-molecular-weight affinity nanosensor herein disclosed. Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the disclosed subject matter belongs. Although methods and materials similar or equivalent to those described herein can be used in its practice, suitable methods and materials are described below.
It is to be noted that the term “a” entity or “an” entity refers to one or more of that entity. As such, the terms “a”, “an”, “one or more”, and “at least one” can be used interchangeably herein. The terms “comprising,” “including,” and “having” can also be used interchangeably. In addition, the terms “amount” and “level” are also interchangeable and can be used to describe a concentration or a specific quantity. Furthermore, the term “selected from the group consisting of” refers to one or more members of the group in the list that follows, including mixtures (i.e., combinations) of two or more members.
The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within 3 or more than 3 standard deviations, per the practice in the art. Alternatively, “about” can mean a range of up to +/−20%, up to +/−10%, up to +/−5%, or alternatively up to +/−1% of a given value. Alternatively, with respect to biological systems or processes, the term can mean within an order of magnitude, preferably within 5-fold, and more preferably within 2-fold, of a value. As used here, the term “coupled” refers to the connection of a system component to another system component by any suitable means known in the art. The type of coupling used to connect two or more system components can depend on the scale and operability of the system. For example, and not by way of limitation, coupling of two or more components of a system can include connecting the nanosensor to the substrate platform or coupling the enrichment chamber to the sensing chamber via the channel.
As used herein, the term “aptamer” means a stable single-stranded oligonucleotide (e.g., DNA, RNA, Xeno Nucleic Acid (XNA)), or peptide that binds to a specific target analyte. In certain embodiments, the aptamer binds with high affinity and specificity to the target analyte.
In certain embodiments, the disclosed subject matter provides a microdevice as described herein coupled with a wireless interface. The output signal can be a raw data stream that can be used to provide a useful value of the measured target analyte concentration. The wireless interface can include a capacitance digital converter coupled with the microdevice and adapted to produce a digital signal representing a measurement of the target analyte in the bodily fluid of the subject; a microcontroller coupled with the capacitance digital converter; and a transponder coupled with the microcontroller to transmit the digital signal received from the capacitance digital converter to an external reader.
The NanosensorThe disclosed subject matter provides a nanosensor for monitoring a target analyte. In certain embodiments, the nanosensor utilizes a pair of conductance sensors on a substrate platform, wherein one of the pair of sensors can be functionalized with receptors for binding the target analyte and the other sensor can be functionalized with receptors that can be insensitive to the target analyte. In certain embodiments, the nanosensor utilizes a single conductance sensor on a substrate platform, wherein the sensor can be functionalized with receptors for binding the target analyte. In certain embodiments, the receptors are natural polymers, synthetic polymers, peptides, antibodies, aptamers, or small molecules. In certain embodiments, the nanosensor does not require the sensor to be functionalized with a receptor, wherein the target analyte itself changes the conductance of the sensor.
The nanosensor can be fabricated of biocompatible materials to prevent adverse responses of the surrounding tissue. These include the substrate and passivation materials (e.g., PET and parylene), the sensing and reference receptors (e.g., natural polymers, synthetic polymers, peptides, antibodies, aptamers, or small molecules), and the glucose-permeable hydrogel coating. In addition, the functional, dielectric and metallization materials (e.g., graphene, hexagonal boron nitride (h-BN) and gold) are also biocompatible when their uptake by individual cells can be avoided. Thus, inflammatory, allergic, immunogenic, cytotoxic, and genotoxic responses of tissue to the microdevice can be minimized.
In certain embodiments, the sensor can be made of graphene. Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional honeycomb lattice. In certain embodiments, the FET sensing element with graphene as the conducting channel has an electric resistance of about 0.1 kΩ-about 3 kΩ In certain embodiments, graphene as the conductance channel has an electric resistance of about 0.1 kΩ-about 3 kΩ about 0.25 kΩ-about 2.75 kΩ about 0.5 kΩ-about 2.5 kΩ about 0.75 kΩ-about 2.25 kΩ about 1 kΩ-about 2 kΩ about 1.25 kΩ-about 1.75 kΩ about 1.5 kΩ-about 2 kΩ or about 2 kΩ-about 3 kΩ In certain embodiments, graphene as the conductance channel has an electric resistance of at least about 0.1 kΩ at least about 0.2 kΩ at least about 0.3 kΩ at least about 0.4 kΩ at least about 0.5 kΩ at least about 0.6 kΩ at least about 0.7 kΩ at least about 0.8 kΩ at least about 0.9 kΩ at least about 1 kΩ at least about 1.2 kΩ at least about 1.4 kΩ at least about 1.6 kΩ at least about 1.8 kΩ at least about 2 kΩ at least about 2.2 kΩ at least about 2.4 kΩ at least about 2.6 kΩ at least about 2.8 kΩ at least about 3 kΩ at least about 4 kΩ at least about 5 kΩ at least about 6 kΩ at least about 7 kΩ at least about 8 kΩ at least about 9 kΩ or at least about 10 kΩ. In certain embodiments, graphene as the conductance channel has an electric resistance of no more than about 0.1 kΩ no more than about 0.2 kΩ no more than about 0.3 kΩ no more than about 0.4 kΩ no more than about 0.5 kΩ no more than about 0.6 kΩ no more than about 0.7 kΩ no more than about 0.8 kΩ no more than about 0.9 kΩ no more than about 1 kΩ no more than about 1.2 kΩ no more than about 1.4 kΩ no more than about 1.6 kΩ no more than about 1.8 kΩ no more than about 2 kΩ no more than about 2.2 kΩ no more than about 2.4 kΩ no more than about 2.6 kΩ no more than about 2.8 kΩ no more than about 3 kΩ no more than about 4 kΩ no more than about 5 kΩ no more than about 6 kΩ no more than about 7 kΩ no more than about 8 kΩ no more than about 9 kΩ or no more than about 10 kΩ.
The graphene monoatomic sheet can have the ultimate thinness (0.34 nm) of any known material and possesses unparalleled mechanical strength (Young's modulus: 1 TPa), adheres strongly to underlying substrates, and can be highly flexible, optically transparent, and chemically stable, thereby holding the potential to enable new, transformative methods for detection of biological analytes. The monoatomic structure as well as exceptional electric conductivity (˜1738 S/m) and charge carrier mobility (2×105 cm2/Vs) of graphene can be exploited to enable highly sensitive analyte detection. Holding the potential to enable new, distinctly transformative methods for detection of biological analytes, graphene has been used for electrochemical or affinity detection of analytes such as DNA and proteins, and for electrochemical detection of glucose.
In certain embodiments, the graphene sensor includes a single layer sheet. In certain embodiments, the graphene sensor includes a multilayered sheet. In certain embodiments, the graphene sensor includes at least one layer of graphene. In certain embodiments, the graphene sensor includes at least two layers of graphene, at least three layers of graphene, or at least four layers of graphene. In certain embodiments, the graphene sheet can be formed by mechanical exfoliation, chemical exfoliation, chemical vapor deposition, or silicon carbide. In certain embodiments, the graphene sheet can be formed by chemical vapor deposition (CVD). In certain embodiments, the graphene sheet can be formed by, mechanical exfoliation, which can include the removal of a layer of graphene from a block of graphite using tape or other sticky substance. Exemplary techniques for fabrication of the graphene sheet are illustrated in
The nanosensors as disclosed herein can be highly sensitive, as changes in surface charge due to the presence of the target analyte near the sensor or the target analyte binding effectively penetrates the bulk of the atomically thin graphene, leading to a detectable signal even at low target analyte concentrations.
In using graphene as a functional material on a flexible substrate, the nanosensors disclosed herein can be miniaturized and mechanically flexible for placement on a substrate platform. In certain embodiments, the substrate platform can be rigid. In certain embodiments, the substrate platform can be flexible. The monoatomic thickness can allow the graphene nanosensor to be highly miniaturized. Miniaturization can drastically reduce distances over which diffusive analyte (e.g., glucose) transport occurs, leading to a rapid response to target analyte changes in a bodily fluid. In certain embodiments, the change in target analyte levels can be detected within about 7 to about 60 seconds. In certain embodiments, the change in target analyte levels are detected within about 10 to about 50 seconds, about 12 to about 45 seconds, about 15 to about 40 seconds, about 17 to about 35 seconds, or about 20 to about 30 seconds. In certain embodiments, the change in target analyte levels can be detected within about 5 seconds, about 6 seconds, about 7 seconds, about 8 seconds, about 9 seconds, about 10 seconds, about 11 seconds, about 12 seconds, about 13 seconds, about 14 seconds, about 15 seconds, about 16 seconds, about 17 seconds, about 18 seconds, about 19 seconds, about 20 seconds, about 21 seconds, about 22 seconds, about 23 seconds, about 24 seconds, about 25 seconds, about 26 seconds, about 27 seconds, about 28 seconds, about 29 seconds, about 30 seconds, about 31 seconds, about 32 seconds, about 33 seconds, about 34 seconds, about 35 seconds, about 36 seconds, about 37 seconds, about 38 seconds, about 39 seconds, about 40 seconds, about 41 seconds, about 42 seconds, about 43 seconds, about 44 seconds, about 45 seconds, about 46 seconds, about 47 seconds, about 48 seconds, about 49 seconds, about 50 seconds, about 51 seconds, about 52 seconds, about 53 seconds, about 54 seconds, about 55 seconds, about 56 seconds, about 57 seconds, about 58 seconds, about 59 seconds, or about 60 seconds, or about 1 minute, 2 minutes, 3 minutes, 4 minutes, or 5 minutes. In certain embodiments, the device response time can be within about 1 to about 10 minutes, about 2 to about 9 minutes, about 3 to about 8 minutes, about 4 to about 7 minutes, or about 5 to about 6 minutes. In certain embodiments, the response times of the device can be at least 1 minute, at least about 2 minutes, at least about 3 minutes, at least about 4 minutes, at least about 5 minutes, at least about 6 minutes, at least about 7 minutes, at least about 8 minutes, at least about 9 minutes, or at least about 10 minutes. In certain embodiments, the response time can be between about 1.5 to about 2.5 minutes, which is at least 2-3 times as rapid as existing CGM devices. The decreased response time and aptamer-target analyte binding time can allow real-time detection of changes in the target analyte concentrations. The decreased response time and aptamer-target analyte binding time can further allow for the detection of the disclosed system to be continuous over time.
The microdevices as disclosed herein can also be mechanically flexible because of the use of flexible materials, including graphene on a flexible substrate. Thus, the device can readily conform to the local tissue geometry, and minimize irritation and injury to a tissue or organ (e.g., an eye) during the sensor placement, operation and replacement. In certain embodiments, the miniature size of the device can also prevent the obstruction of vision when integrated on a contact lens. The intimate contact can also facilitate exchange of glucose between the device and tears, leading to improved sensitivity and reliability. Therefore, because of the miniaturization and flexibility, the device can be highly compatible with contact lens-based noninvasive CGM.
To reduce protein adsorption and biofouling, in certain embodiments the entire nanosensor can be coated in a biocompatible hydrogel. In certain embodiments, the nanosensor can be coated with a thin hydrogel layer. In certain embodiments, the hydrogel can be permeable to the target analyte. In certain embodiments, the hydrogel can be permeable to glucose. In certain embodiments, the biocompatible hydrogen can be synthesized in situ. Exemplary techniques for fabrication of the hydrogel are discussed in further detail in Example 10. Hydrogels can be made by any other commonly understood method.
In certain embodiments, the hydrogel can include, but is not limited to, at least one of poly(hydroxyethyl-methacrylate (PHEMA), hydroxyethyl methacrylate (HEMA), tetraethyleneglycol diacrylate (TEGDA), polyethyleneglycol methacylate (PEGMA), or N-[tris(hydroxymethyl)methyl]-acrylamide (HMMA). In certain embodiments, the hydrogel includes hydroxyethyl methacrylate (HEMA), tetraethyleneglycol diacrylate (TEGDA), polyethyleneglycol methacylate (PEGMA) and N-[tris(hydroxymethyl)methyl]-acrylamide (HMMA). In certain embodiments, the hydrogel includes a combination of hydroxyethyl methacrylate (HEMA), tetraethyleneglycol diacrylate (TEGDA), polyethyleneglycol methacylate (PEGMA) and N-[tris(hydroxymethyl)methyl]-acrylamide (HMMA). In certain embodiments, the hydrogel includes hydroxyethyl methacrylate (HEMA), tetraethyleneglycol diacrylate (TEGDA), polyethyleneglycol methacylate (PEGMA) and N-[tris(hydroxymethyl)methyl]-acrylamide (HMMA) at a ratio of 86:3:5.5 mol %.
In certain embodiments, the thickness of the hydrogel layer ranges from about 20-50 μm. In certain embodiments the hydrogel layer can be no thicker than about 5 μm, about 6 μm, about 7 μm, about 8 μm, about 9 μm, about 10 μm, about 11 μm, about 12 μm, about 13 μm, about 14 μm, about 15 μm, about 16 μm, about 17 μm, about 18 μm, about 19 μm, about 20 μm, about 21 μm, about 22 μm, about 23 μm, about 24 μm, about 25 μm, about 26 μm, about 27 μm, about 28 μm, about 29 μm, about 30 μm, about 31 μm, about 32 μm, about 33 μm, about 34 μm, about 35 μm, about 36 μm, about 37 μm, about 38 μm, about 39 μm, about 40 μm, about 41 μm, about 42 μm, about 43 μm, about 44 μm, about 45 μm, about 46 μm, about 47 μm, about 48 μm, about 49 μm, or about 50 μm, In certain embodiments, the thickness of the hydrolayer can be between about 20 μm to about 50 μm.
In certain embodiments, the nanosensor can be constructed on a substrate platform. In certain embodiments, the substrate can be fabricated on the final substrate (e.g., a contact lens). In certain embodiments, the substrate can be fabricated on a thin flexible film and the nanosensor device (including the thin flexible film) is attached to the final substrate platform (e.g., a contact lens). In certain embodiments, the substrate platform and the thin layer film can be made from the same material. In certain embodiments, the substrate platform and thin later film can be made from different material. In certain embodiments, the nanosensor can be formed on a substrate platform that is then formed/molded (e.g., by heating) into a contact lens shape.
In certain embodiments, the nanosensor can be on the inside the contact lens (i.e., towards the eye). In certain embodiments, the nanosensor can be on the outside of the contact lens (i.e., towards the eyelid).
In accordance with certain embodiment, the nanofilms can be transferred in a vacuum to prevent air bubbles from being trapped between the graphene, dielectric layer, and the substrate. In certain embodiments, the nanofilm surfaces can also be treated by heat or low-power oxygen plasma to further improve adhesion.
The design parameters can be varied without departing from the scope of the disclosed subject matter. Such design parameters include, for example, the number and dimensions of atomic layers and substrate platform layers, shape and dimensions of the graphene, molecular weight of the sensing receptor, and the thickness of the hydrogel coating.
Single ChannelA set of sensing receptors functionalized on the conductance sensor can bind to the target analyte. In certain embodiments, the sensing receptor binds specifically to the target analyte. In certain embodiments, the sensing receptor can bind reversibly or irreversibly to the target analyte. In certain embodiments, the sensing receptor can bind reversibly to the target analyte. In certain embodiments, the reference receptor can bind reversibly to essentially all analytes. In certain embodiments, the sensing receptor can bind to more than one target analyte.
In certain embodiments, target analyte binding of the sensing receptor can change the charge density on the sensor surface, inducing changes in the carrier concentration of the sensor.
In certain embodiments, the sensing polymer can bind specifically to the target analyte. Target analyte binding of the sensing polymer can change the charge density on the sensor surface, inducing changes in the carrier concentration of the sensor. In certain embodiments, the polymers can bind reversibly with essentially all analytes. In certain embodiments, the sensing polymer can bind reversibly with the target analyte.
In certain embodiments, the nanosensor can be configured as a solution-gated graphene-based FET (GFET) in that the graphene (e.g., 605) is the conducting channel, which can be formed between two electrodes (source (e.g., 608) and drain (e.g., 609)) on an insulating substrate surface (e.g., 601) (
The substrate or platform surface can be one or multi-layered. For example, the substrate or platform surface can include two layers (see
A monolayer of the synthetic glucose responsive polymer (e.g., 611) can be attached to the graphene surface via π-π stacking interactions (
In certain embodiments, the nanosensor can be not functionalized with a receptor. The charge of the target analyte can change the charge density on the sensor surface, inducing changes in the carrier concentration of the sensor. In certain embodiments, such a sensor can be used to test a sample or bodily fluid. In certain embodiments, such a sensor can be used to test the pH or electrolyte concentration of a sample or bodily fluid. In certain embodiments, such a sensor can be used to test for the presence or absence of an analyze carrying a charge or capable of eliciting a charge by any means. For example, but not limited to, the analyte can interact with a substance present near the sensor that would allow a charge or change in a charge to occur.
In certain embodiments, the nanosensor can be configured as a solid-gated FET device, in which a graphene sheet, serving as the conducting channel, connected the source and drain electrodes on a dielectric layer, which in turn lies above the gate electrode on the substrate (
In certain embodiments, when the nanosensor is not functionalized with receptors, the presence of ions near the sensor can be detected. The magnitude of the electric potential can depend on the ion concentration (e.g., H+). In certain embodiments, the pH level can be determined by measuring the graphene's electric properties such as its transfer characteristics and conductance, which can be directly related to the carrier concentration. To allow a high level of integration while avoiding the need for high gate voltages, the nanosensor can use about 20 nm thick HfO2, a material with a high dielectric constant (κ≈20, compared to κ≈3.9 for SiO2), as the dielectric layer to provide a high gate capacitance (˜1 μF/cm2). This in general can allow the Dirac point, at which the drain-source current IDS achieves its minimum, to be observed at a lower gate voltage.
In certain embodiments, the electrode wire can be, for example, but not limited to Ag/AgCl, Ag, Pt, or combinations thereof.
In certain embodiments, the dielectric nanolayer can be made from material such as, but not limited to hexagonal boron nitride (h-BN), HfO2, parylene, SiO2, Si3N4, or combinations thereof.
In certain embodiments, the gate electrode can be made from material such as, but not limited to ITO, Ti/Pd/Pt, gold, copper, chrome, or mixtures thereof.
In certain embodiments, the source and drain electrodes, can be separately made from material such as, but not limited to ITO, Ti/Pd/Pt, chromium, gold, chrome, or combinations thereof.
In certain embodiments, the polymer substrate and or thin layer film can be made from material such as, but not limited to polyethylene terephthalate (PET), polycarbonate polystyrene, polymethyl methacrylate (PMMA), polymacon, silicones, fluoropolymers, silicone acrylate, fluoro-silicone/acrylate, poly hydroxyethyl methacrylate, or combinations thereof.
In certain embodiments, the polymer coating can be made from material such as, but not limited to, parylene, polyimide, organic polymer, hydrophobic polymer, or combinations thereof. In certain embodiments, the nanosensor can be covered with a polymer coating except for the functionalized part of the graphene sheet.
In certain embodiments, the sensing polymer can be, for example, but not limited poly(N-hydroxyethylacrylamide-ran-3-acrylamidophenylboronic acid) (PHEA-ran-PAAPBA) and pyrene-terminated poly(3-acrylamidophenylboronic acid) (py-PAPBA). In certain embodiments, the copolymer can be liner or branched. Additional receptor polymers are discussed below.
In certain embodiments, the dimensions of the graphene conducting channel in the single channel graphene sensor can be a length of about 10-about 20 μm by a width of about 10-about 20 μm by a thickness of about 1-about 10 nm. In certain embodiments, the graphene channel in the sensor can be about 20×10 μm2. In certain embodiments, the graphene conducting channel can be functionalized with a polymer.
In certain embodiments, the length of the graphene channel in the sensor can be about 10.2-about 19.8 about 10.4-about 19.6 about 10.6-about 19.4 about 10.8-about 19.2 about 11-about 19 about 11.2-about 18.8 about 11.4-about 18.6 about 11.6-about 18.4 about 11.8-about 18.2 about 12-about 18 about 12.2-about 17.8 about 12.4-about 17.6 about 12.6-about 17.4 about 12.8-about 17.2 about 13-about 17 about 13.2-about 16.8 about 13.4-about 16.6 about 13.6-about 16.4 about 13.8-about 16.2 about 14-about 16 about 14.2-about 15.8 about 14.4-about 15.6 about 14.6-about 15.4 or about 14.8-about 15.2 In certain embodiments, the width of the graphene channel in the sensor can be about 10.2-about 19.8 about 10.4-about 19.6 about 10.6-about 19.4 about 10.8-about 19.2 about 11-about 19 about 11.2-about 18.8 about 11.4-about 18.6 about 11.6-about 18.4 about 11.8-about 18.2 about 12-about 18 about 12.2-about 17.8 about 12.4-about 17.6 about 12.6-about 17.4 about 12.8-about 17.2 about 13-about 17 about 13.2-about 16.8 about 13.4-about 16.6 about 13.6-about 16.4 about 13.8-about 16.2 about 14-about 16 about 14.2-about 15.8 about 14.4-about 15.6 about 14.6-about 15.4 or about 14.8-about 15.2 In certain embodiments, the thickness of the graphene channel in the sensor can be about 1.2-about 9.8 nm, about 1.4-about 9.6 nm, about 1.6-about 9.4 nm, about 1.8-about 9.2 nm, about 2-about 9 nm, about 2.2-about 8.8 nm, about 2.4-about 8.6 nm, about 2.6-about 8.4 nm, about 2.8-about 8.2 nm, about 3-about 8 nm, about 3.2-about 7.8 nm, about 3.4-about 7.6 nm, about 3.6-about 7.4 nm, about 3.8-about 7.2 nm, about 4-about 7 nm, about 4.2-about 6.8 nm, about 4.4-about 6.6 nm, about 4.6-about 6.4 nm, about 4.8-about 6.2 nm, about 5-about 6 nm, about 4.2-about 5.8 nm, about 4.4-about 5.6 nm, about 4.6-about 5.4 nm, or about 4.8-about 5.2 nm.
In certain embodiments, the dimensions of the single channel nanosensor chip can be a length of about 5-about 10 mm by a width of about 5-about 10 mm by a thickness of about 50-about 500 μm. In certain embodiments the graphene sensor can be about 25×10 μm2. In certain embodiments, the total nanosensor can be about 10×10 mm2.
In certain embodiments, the length of the single channel nanosensor chip can be about 5.2-about 9.8 mm, about 5.4-about 9.6 mm, about 5.6-about 9.4 mm, about 5.8-about 9.2 mm, about 6-about 9 mm, about 6.2-about 8.8 mm, about 6.4-about 8.6 mm, about 6.6-about 8.4 mm, about 6.8-about 8.2 mm, about 7-about 8 mm, about 7.2-about 7.8 mm, or about 7.4-about 7.6 mm. In certain embodiments, the width of the single channel nanosensor chip can be about 5.2-about 9.8 mm, about 5.4-about 9.6 mm, about 5.6-about 9.4 mm, about 5.8-about 9.2 mm, about 6-about 9 mm, about 6.2-about 8.8 mm, about 6.4-about 8.6 mm, about 6.6-about 8.4 mm, about 6.8-about 8.2 mm, about 7-about 8 mm, about 7.2-about 7.8 mm, or about 7.4-about 7.6 mm. In certain embodiments, the thickness of the single channel nanosensor chip can be about 75-about 475 μm, about 100-about 450 μm, about 125-about 425 μm, about 150-about 400 μm, about 175-about 375 μm, about 200-about 350 μm, about 225-about 325 μm, or about 250-about 300 μm.
Exemplary techniques for fabrication of the devices illustrated in, for example,
In certain embodiments, one set of receptors (sensing receptors) functionalized on one of the pair of conductance sensors can bind to the target analyte and the other set of receptors (reference receptors) functionalized on the a separate conductance sensor can be insensitive to the target analyte. In certain embodiments, the sensing receptor can bind specifically to the target analyte. In certain embodiments, the sensing receptor can bind reversibly or irreversibly to the target analyte. In certain embodiments, the sensing receptor can only bind reversibly to the target analyte. In certain embodiments, the reference receptor can bind reversibly to essentially all analytes. In certain embodiments, the first and second conductive elements can be essentially identical except for the first conductive element being functionalized with the sensing receptor and the second conductance element being functionalized with a reference receptor. In certain embodiments, binding of the target analyte to the sensing receptor can induce changes in the electrical conductance of the graphene of the first conductive element and conductance of the second conductive element only changes due to fluctuations in environmental parameters. In certain embodiments, the sensing receptor can bind to more than one target analyte.
In certain embodiments, at least two channels are present in the nanosensor. In certain embodiments, at least three channels, at least four channels, or at least five channels can be present in the nanosensor. In certain embodiments, four channels can be present. In certain embodiments, at least one of the multichannel sensors can be functionalized with a reference receptor (e.g., polymer). In certain embodiments, at least two of the sensors can be e functionalized with sensing receptors (e.g., polymers). In certain embodiments, at least two of the sensors can be functionalized with two different sensing receptors (e.g., polymers).
In certain embodiments, target analyte binding of the sensing receptor can change the charge density on the sensor surface, inducing changes in the carrier concentration of the sensor. Meanwhile, the reference receptor does not bind to the target analyte and its associated sensor conductance can change only due to fluctuations in environmental parameters. Thus, differential measurement of the target analyte conductance can allow determination of the target analyte concentration in a bodily fluid.
In certain embodiments, one polymer (sensing polymer) can bind specifically to the target analyte, and the other (reference polymer) is insensitive to the target analyte. Target analyte binding of the sensing polymer can change the charge density on the sensor surface, inducing changes in the carrier concentration of the sensor. Meanwhile, the reference polymer does not bind to the target analyte and its associated sensor conductance could change only due to fluctuations in environmental parameters. Thus, differential measurement of the target analyte conductance can allow determination of the target analyte concentration in a bodily fluid. In certain embodiments, the polymers can bind reversibly with most analytes. In certain embodiments, the polymers can bind reversibly with essentially all analytes. In certain embodiments, the sensing polymer can bind reversibly with the target analyte.
In certain embodiments, the dimensions of the graphene conducting channel in the dual channel graphene sensor can be a length of about 10-about 20 μm by a width of about 10-about 20 μm by a thickness of about 1-about 10 nm. In certain embodiments, the graphene channel in the sensor can be about 20×10 μm2.
In certain embodiments, the length of the graphene channel in the sensor can be about 10.2-about 19.8 about 10.4-about 19.6 about 10.6-about 19.4 about 10.8-about 19.2 about 11-about 19 about 11.2-about 18.8 about 11.4-about 18.6 about 11.6-about 18.4 about 11.8-about 18.2 about 12-about 18 about 12.2-about 17.8 about 12.4-about 17.6 about 12.6-about 17.4 about 12.8-about 17.2 about 13-about 17 about 13.2-about 16.8 about 13.4-about 16.6 about 13.6-about 16.4 about 13.8-about 16.2 about 14-about 16 about 14.2-about 15.8 about 14.4-about 15.6 about 14.6-about 15.4 or about 14.8-about 15.2 In certain embodiments, the width of the graphene channel in the sensor can be about 10.2-about 19.8 μm, about 10.4-about 19.6 μm, about 10.6-about 19.4 μm, about 10.8-about 19.2 μm, about 11-about 19 about 11.2-about 18.8 about 11.4-about 18.6 about 11.6-about 18.4 about 11.8-about 18.2 about 12-about 18 about 12.2-about 17.8 about 12.4-about 17.6 about 12.6-about 17.4 about 12.8-about 17.2 about 13-about 17 about 13.2-about 16.8 about 13.4-about 16.6 about 13.6-about 16.4 about 13.8-about 16.2 about 14-about 16 about 14.2-about 15.8 about 14.4-about 15.6 about 14.6-about 15.4 or about 14.8-about 15.2 In certain embodiments, the thickness of the graphene channel in the sensor can be about 1.2-about 9.8 nm, about 1.4-about 9.6 nm, about 1.6-about 9.4 nm, about 1.8-about 9.2 nm, about 2-about 9 nm, about 2.2-about 8.8 nm, about 2.4-about 8.6 nm, about 2.6-about 8.4 nm, about 2.8-about 8.2 nm, about 3-about 8 nm, about 3.2 about 7.8 nm, about 3.4-about 7.6 nm, about 3.6-about 7.4 nm, about 3.8-about 7.2 nm, about 4-about 7 nm, about 4.2-about 6.8 nm, about 4.4-about 6.6 nm, about 4.6-about 6.4 nm, about 4.8-about 6.2 nm, about 5-about 6 nm, about 4.2-about 5.8 nm, about 4.4-about 5.6 nm, about 4.6-about 5.4 nm, or about 4.8-about 5.2 nm.
In certain embodiments, the dimensions of the dual channel nanosensor chip can be a length of about 8-about 15 mm by a width of about 8-about 15 mm by a thickness of about 50-about 500 In certain embodiments, the total nanosensor chip can be about 15×15 mm2.
In certain embodiments, the length of the dual channel nanosensor chip can about 8.2-about 14.8 mm, about 8.4-about 14.6 mm, about 8.6-about 14.4, about 8.8-about 14.2 mm, about 9-about 14 mm, about 9.2-about 13.8 mm, about 9.4-about 13.6 mm, about 9.6-about 13.4, about 9.8-about 13.2 mm, about 10-about 13 mm, about 10.2-about 12.8 mm, about 10.4-about 12.6 mm, about 10.6-about 12.4, about 10.8-about 12.2 mm, about 11-about 12 mm, about 11.2-about 11.8 mm, or about 11.4-about 11.6 mm. In certain embodiments, the width of the dual channel nanosensor chip can about 8.2-about 14.8 mm, about 8.4-about 14.6 mm, about 8.6-about 14.4, about 8.8-about 14.2 mm, about 9-about 14 mm, about 9.2-about 13.8 mm, about 9.4-about 13.6 mm, about 9.6-about 13.4, about 9.8-about 13.2 mm, about 10-about 13 mm, about 10.2-about 12.8 mm, about 10.4-about 12.6 mm, about 10.6-about 12.4, about 10.8-about 12.2 mm, about 11-about 12 mm, about 11.2-about 11.8 mm, or about 11.4-about 11.6 mm. In certain embodiments, the thickness of the dual channel nanosensor chip can be about 75-about 475 μm, about 100-about 450 μm, about 125-about 425 μm, about 150-about 400 μm, about 175-about 375 μm, about 200-about 350 μm, about 225-about 325 μm, or about 250-about 300 μm.
The slender graphene strips (e.g., 105) can lie on a dielectric nanolayer (e.g., 106). In certain embodiments, the graphene strips can be two separate strips. The dielectric nanolayer can passivate a gate electrode (e.g., 107) and can make contact with a source (e.g., 108) and drain electrode (e.g., 109). In certain embodiments, these nanolayers can lie on a polymer substrate/substrate platform (e.g., 101) and can be covered with a thin polymer layer (e.g., 110) with the exception of the conducting-channel graphene (e.g., 103, 104), which can be functionalized with a target specific receptor (e.g., glucose-binding polymer (the sensing module)) (e.g., 111) or a target insensitive receptor (e.g., glucose-insensitive polymer (the reference module)) (e.g., 112). In certain embodiments, nanolayers and polymer layers can be all flexible and biocompatible.
In certain embodiments, the dielectric nanolayer can be made from material such as, but not limited to hexagonal boron nitride (h-BN), parylene, SiO2 and Si3N4, or combinations thereof.
In certain embodiments, the gate electrode can be made from material such as, but not limited to ITO, Ti/Pd/Pt, gold, copper, chrome, or mixtures thereof.
In certain embodiments, the source and drain electrodes, can be separately made from material such as, but not limited to ITO, Ti/Pd/Pt, chromium, gold, chrome, or combinations thereof.
In certain embodiments, the substrate platform (e.g., polymer substrate) and/or thin layer film can be made from material such as, but not limited to polyethylene terephthalate (PET), polycarbonate polystyrene, polymethyl methacrylate (PMMA), polymacon, silicones, fluoropolymers, silicone acrylate, fluoro-silicone/acrylate, poly hydroxyethyl methacrylate, or combinations thereof.
In certain embodiments, the polymer coating can be made from material such as, but not limited to, parylene, polyimide, organic polymer, hydrophobic polymer, or combinations thereof. In certain embodiments, the nanosensor is covered with a polymer coating except for the functionalized part of the graphene sheet.
In certain embodiments, the sensing polymer can be, for example, but not limited poly(N-hydroxymethylacrylamide-ran-3-acrylamidophenylboronic acid) (PHEA-ran-PAAPBA) and pyrene-terminated poly(3-acrylamidophenylboronic acid) (py-PAPBA). In certain embodiments, the copolymer can be liner or branched. Additional receptor polymers are discussed below.
During operation, the conducting-channel graphene can be subjected to a gate voltage (e.g., between ±300 mV) with respect to the gate electrode underneath, and the current through the graphene under a bias voltage (10-50 mV) between the source and drain, which can be kept sufficiently small to limit the potential leakage current into the hydrogel coating well below the threshold (˜10 μA/mm2) required to prevent undesirable electrochemical effects in tissue. In certain embodiments, the bias voltage is between about 10 to about 50 mV. In certain embodiments, the bias voltage is between about 10 to about 50 mV, about 12 to about 48 mV, about 14 to about 46 mV, about 16 to about 44 mV, about 18 to about 42 mV, about 20 to about 40 mV, about 22 to about 38 mV, about 24 to about 36 mV, about 26 to about 34 mV, or about 28 to about 32 mV.
Exemplary techniques for fabrication of the devices illustrated in, for example,
In various embodiments of the disclosed subject matter, the sensor can be used to determine the level of a target analyte in the body, for example oxygen, lactase, insulin, hormones, cholesterol, medicaments, viruses, or the like. In certain embodiments, the receptors that identify the target analyte can be natural polymers, synthetic polymers, peptides, antibodies, aptamers, or small molecules.
In certain embodiments, the receptor can be a polymer. The sensing polymer can include one in which at least one monomer or moiety interacts with the target analyte. Interaction between the target analyte and the sensing polymer results in a change in conductance of the sensor. In certain embodiments, the reference polymer can include a polymer whose moieties or monomers do not interact with the target analyte. In certain embodiments, the polymer can include at least two monomers, at least three monomers, at least four monomers, at least five monomers, at least six monomers, at least seven monomers, at least eight monomers, at least nine monomer, or at least ten monomers.
In certain embodiments, the target analyte can be glucose. When the target analyte is glucose, through proper adjustment of the composition percentage of the boronic acid moieties on the polymer and polymer concentrations, the polymer can detect and differentiate glucose from other monosaccharides and disaccharides. Applying this polymer to the nanosensor as disclosed herein can enable highly reliable, continuous monitoring of glucose in bodily fluids.
As noted, the binding between the polymer and the analyte of interest can be reversible. For example, the binding and dissociation between the target analyte and the sensing polymer can be an equilibrium phenomenon driven by the concentration of the analyte in the conducting channel. The amount of the analyte bound with the sensing polymer depends on the concentration of the analyte in the conducting channel.
In one embodiment, a suitable polymer having boronic acid moieties can be formed as a copolymer of at least two monomers, where one of the monomers includes at least one boronic acid functional group. A copolymer can be synthesized with these monomers via classic free radical copolymerization processes. In certain embodiments, a suitable polymer can include, but is not limited to, a polymer that contains boronic acid groups, or other receptor groups that recognize the given analytes. In one embodiment, the polymer can be phenyl acrylamide (PAM). In another embodiment, the polymer can be PAM-ran-PAAPBA, which is an amphiphilic copolymer containing two components, hydrophilic polymer segment phenyl acrylamide (PAM) and hydrophobic polymer segment poly(3-acrylamidophenylboronic acid) (PAAPBA). In yet another embodiment, the polymer can be PAM-ran-PPAM, which is an amphiphilic copolymer containing two components, hydrophilic polymer segment phenyl acrylamide (PAM) and hydrophobic polymer segment polymeric allylamine (PPAM).
In certain embodiments, basic monomers, such as, but not limited to, N,N-dimethylacrylamide can be used to increase the ionization of boronate upon binding with diols.
In certain embodiments, the copolymer can be liner or branched. In certain embodiments, the copolymer can include hydrophilic motifs (e.g., polymeric allylamine (PAM), hydroxyethyl methacrylate (HEMA)). In certain embodiments, the copolymers can be in situ gelation pre-polymers. In certain embodiments, in situ gelation of polymers is one in which a solution of polymers can form a hydrogel on the sensor chip by methods of heating and UV irradiation.
In certain embodiments the polymer can be conjugated to a substance that can immobilize the polymers on the graphene sensor. In certain embodiments, the substance-terminated polymers can be irreversibly attached to graphene with strength comparable to covalent attachment. In certain embodiments, the substance can be pyrene. A pyrene-terminated polymer can be irreversibly attached to graphene using a sticky point for μ-μ stacking interactions without disrupting the graphene's conjugation or altering its electronic properties, can be synthesized.
The polymer sensors can undergo a viscosity change as well as a permittivity change when interacting with glucose molecules, as discussed in US Patent Application Publication No. 20120043203, assigned to the common assignee, the disclosure of which is incorporated herein by reference in its entirety.
The sensing polymer can include boronic acid groups, which can bind to glucose molecules at a 2:1 ratio to reversibly form cyclic esters of boronic acid, while having almost no response to other potential interferents, such as fructose, galactose, and sucrose. Below is a representative schematic of the reaction:
In certain embodiments, the polymer can include as least one boronic acid group, at least two boronic acid group, at least three boronic acid group, at least four boronic acid group, at least five boronic acid group, at least six boronic acid group, at least seven boronic acid group, at least eight boronic acid group, at least nine boronic acid group, at least 10 boronic acid group. The process can cause the overall ionization equilibrium to shift from neutral/insoluble boronic acid moieties to anionic/hydrophilic boronate, thereby changing the surface charge density. This can result in a change in the carrier concentration within the bulk of the atomically thin graphene in the sensing module, and hence a change in the graphene conductance. In certain embodiments, the reference polymer can be glucose-insensitive, the graphene conductance in the reference module would change only due to fluctuations in environmental parameters. Thus, differential measurement of the graphene conductance can allow determination of tear glucose concentration.
To estimate the nanosensor performance, Langmuir's adsorption isotherm can relate the glucose concentration in ISF (c) to the surface density of boronic acid-bound glucose molecules. It can then be shown that the sensitivity of the graphene conductance (G) is approximately:
(dG/G)/dc≈γmaxKd/[2N(Kd+c)2], (1)
where N is the graphene's charge carrier density, γmax the surface density of immobilized boronic acid groups, and Kd the equilibrium dissociation constant of the binding system. Thus, for typical material and binding properties (N˜1015 m−2, γmax˜105 μm−2 and Kd˜10 mM), over a desired glucose concentration range of 0.5-30 mg/dL (which encompasses the hypoglycemic, normoglycemic and hyperglycemic regimes), the nanosensor sensitivity ˜0.5%-0.4%/(mg/dL). For an estimated conductance measurement resolution of 0.1%, glucose concentration can be measured at a resolution of ˜0.7-0.02%, which allows accurate affinity detection of glucose in tears.
In certain embodiments, in order to screen out effects not caused by the target analyte, for example, environmental factors such as temperature or other analytes, the reference chamber can include a graphene sensor that is functionalized with another polymer (the reference polymer). The reference polymer cannot bind with the target analyte. Also, the reference polymer cannot bind with or otherwise react with any other substance in the bodily fluid to impact the property of the reference solution in a similar way as the target analyte impacts the corresponding property in the sensing polymer. The reference polymer and sensing polymer can, however, respond similarly to non-target analytes and environmental conditions. The reference polymer can be selected to have similar hydrophilic blocks to those in the sensing polymer, but have no phenylboronic acid moieties. For example, glucose-unresponsive PAA or PHEAA can be used as a reference polymer for glucose detection. The charge and viscosity of PAA (or PHEAA) polymers can be glucose-independent. The analyte-free charge of the sensing polymer can be similar to that of the reference polymer.
In certain embodiments, the polymers can be not immobilized on the graphene sensors. In these embodiments, the proximity of the change in the polymer charge can be sensed by the graphene sensor. In certain embodiments, the polymers can be sequestered near the sensors by the presence of a hydrogel.
In accordance with another embodiment, alternative, covalent attachment methods, e.g., by using residue hydroxyl on graphene to tailor the polymer design can be used. In accordance with a further embodiment, a more basic monomer, such as N,N-dimethylacrylamide, can be used to prepare the polymer, which is known to enable the ionization of boronate upon binding with diols under physiologic conditions.
In certain embodiments, the disclosed receptor can change its structure upon the binding of the target molecules or analytes. The receptor can be coupled to the linker in the first confirmation. The structure of the receptor can be altered into the second confirmation when the target molecules bind to the aptamer. For example, in the absence of insulin, the guanine-rich IGA3 aptamer can be unfolded in the solution or form G-quartet structure as a result of Hoogsteen base pairing. Upon capture of insulin, the existing G-quartet structures can switch to stable, compact parallel or antiparallel G-quadruplex structures. These conformational changes can move the electron-rich aromatic nucleotide strands and insulin to the close proximity of the nanosensor surface, resulting in the direct binding of nucleotide or amino acids in insulin with the nanosensor surface. Such conformation can transfer electrons from either insulin or the deformed IGA3 aptamer into the surface of nanosensor and induce conductance change on the surface of the nanosensor.
Target AnalyteIn various embodiments of the disclosed subject matter, the sensor can be used to determine the level of a target analyte in the body, for example oxygen, lactase, insulin, hormones, cholesterol, medicaments, viruses, ions, or the like. The sensor can use any known method to provide an output signal indicative of the concentration of the target analyte. The output signal can be typically a raw data stream that can be used to provide a useful value of the measured target analyte concentration. In certain embodiments, before the device is used to detect or monitor a target analyte, it can be first calibrated using samples containing known amount of the target analyte to obtain correlations between sensor response (e.g., capacitance readout) and the known concentration of the calibration sample. Thereafter, in the monitor of the target analyte, the pre-established correlations can be used to interpret the output signals of the sensor and determine the presence and/or concentration of the target analyte in a test sample.
In certain embodiments, the nanosensor as disclosed herein can enable highly reliable monitoring of a target analyte in a sample. In certain embodiments, the sample can be a bodily fluid, a non-bodily fluid liquid, or a laboratory sample. In certain embodiments, the nanosensor can be used to detect the change in the pH of a sample. In certain embodiments the nanosensor can be used to continuously monitor the change in pH of a sample. In certain embodiments, the nanosensor can be used to measure the amount or change in the amount of a target analyte in a sample. For example, the nanosensor can be part of a stand alone device that monitors the target analyte in a sample added to the device (e.g., a piece of lab equipment or home monitor).
In certain embodiments, the nanosensor as disclosed herein can enable highly reliable, continuous monitoring of glucose in bodily fluids. In certain embodiments, the bodily fluid can be tears, blood, saliva, mucus, interstitial fluid, spinal fluid, intestinal fluid, amniotic fluid, lymphatic fluid, pericardial fluid, peritoneal fluid, pleural fluid, semen, vaginal secretions, sweat, and synovial fluid of the subject.
In certain embodiments, tear fluid can be used to measure target analyte concentrations. Tear fluid can be easily accessible, and the eye is an ideal candidate for the placement of a microdevice (e.g., a contract lens with a nanosensor coupled to it) to monitor analytes. In certain embodiments, tear fluid can be used to test, for example, lactate levels or glucose levels.
In certain embodiments of the disclosed subject matter, the nanosensor can be used to monitor glucose as the target analyte. In these embodiments, the nanosensor can measure a concentration of glucose or a substance indicative of the concentration or presence of the glucose by using a specific receptor (e.g., polymer etc. . . . ) in the nanosensor. In certain embodiments, the present microdevice can include a combination of graphene, a novel biosensing nanomaterial, and a contact lens platform to enable noninvasive CGM in tear fluid.
Glucose concentration in tears has been found to range from 1-6.2 mg/dL in healthy individuals and up to 26 mg/dL in diabetic persons. Significant correlations have been found between tear and blood glucose concentrations, with deviations attributable to artifacts such as inconsistent tear collection methods. Tear fluid can include basal tear, which keeps cornea wet and nourished, and reflex tear, which is induced by irritation of the eye due to foreign particles or irritant substances. No significant differences in glucose concentration have been found in basal and reflex tears.
A contact lens-based graphene affinity nanosensor (
The nanosensor can include the glucose-binding polymer with boronic acid groups (e.g., polymer poly(acrylamide-ran-3-acrylamidophenyl boronic acid) (PAA-ran-3PAAPBA)) that can bind with glucose at 2:1 ratio to form cyclic esters. The resulting changes in physical (e.g., viscometric and dielectric) properties of the polymer can be measured with microfabricated devices, enabling specific measurement of glucose concentrations. The nanosensor can thus be highly sensitive and accurate at clinically important glucose concentrations in tears, in particular in the low, hypoglycemic regime (below 1 mg/dL). In certain embodiments, the glucose concentrations can be measured at a resolution of about 2 μg/dL-about 3 μg/dL. In certain embodiments, the glucose concentrations can be measured with the disclosed microdevice at a resolution of about 1 μg/dL-about 10 μg/dL, 2 μg/dL-about 9 μg/dL, 3 μg/dL-about 8 μg/dL, 4 μg/dL-about 7 μg/dL, or 5 μg/dL-about 6 μg/dL. In certain embodiments, the glucose concentrations can be measured with the disclosed microdevice at a resolution of at least about 1 μg/dL, at least about 2 μg/dL, at least about 3 μg/dL, at least about 4 μg/dL, at least about 5 μg/dL, at least about 6 μg/dL, at least about 7 μg/dL, at least about 8 μg/dL, at least about 9 μg/dL, at least about 10 μg/dL, at least about 12.5 μg/dL, at least about 15 μg/dL, at least about 17.5 μg/dL, or at least about 20 μg/dL.
The nanosensor can also be used for other applications. In addition to diabetes, the proposed CGM microdevice can also be used for glucose monitoring for other diseases (e.g., glycogen storage disease and hyperinsulinaemic hypoglycaemia). In some embodiments, the nanosensor can be used for detecting insulin molecules. For example, the nanosensor can include insulin-specific receptors such as guanine-rich IGA 3 aptamers. For example, the binding of insulin to aptamer IGA3 can alter the carrier concentration in the channel of nanosensor. The altered carrier concentration can further change conductance and current of the channel layer. The conductance and current of the channel layer can be measured to determine the insulin concentration. The disclosed nanosensor can detect insulin concentrations as low as about 1 nM. For example, the graphene nanosensor can monitor insulin levels ranging from about 1 nM to about 500 nM in real time.
The method can be extended to other metabolites, such as lactate, fatty acids, cysteines and homocysteines. For example, in emergency medicine, lactate monitoring can be used to predict possible organ failure of trauma patients, organ transplant patients, and patients with other critical conditions. In non-limiting embodiments, the method can include modifying the aptamer to adjust a specificity of the nanosensor to the target analyte. For example, the aptamers on the surface of the nanosensor can be replaced with other receptors which can be show improved specificity for certain target analytes such as insulin and glucose.
Further, the methods disclosed herein can be used as a reliable method for long-term monitoring of metabolites. Such methods can have great military significance. For example, a miniature device for glucose detection with fully electronic readout would have significant applications in protecting armed forces in the field. It can also provide a platform to enable the delivery of drug treatments and nutritional supplements to protect and enhance performance in military personnel.
Moreover, the disclosed method can be applied to the diagnosis of disease. For example, the development of boronic acid-based glucose sensing systems can be extended to other analytes, such as human viruses and bacteria, as many of those microorganisms carry glycoproteins on the exterior surface that can be targeted by the boronic acid based binding motifs.
Additionally, the disclosed method can be applied to a noninvasive method for monitoring cancer treatment. For example, receptors can be designed to that bind to target microparticles associated with cell apoptosis. The receptors can be specific for apoptosis of the cancer cells. In certain embodiments, the microdevice can be used to track overall cell apoptosis to monitor when levels of cell death before they become too toxic. In certain embodiments, the microdevice is able to detect the level of cancer cells in the bodily fluid.
Furthermore, the methods disclosed herein can be used as a reliable method for determining the drug distribution of a treatment regimen in order to maximize the therapeutic effects of the drug. In such methods, the receptors of the device can designed to bind to the drug found in the bodily fluid. For example, ocular drug delivery is a major challenge to pharmacologists due to its unique anatomy and physiology (e.g., different layers of cornea, sclera, and retina including blood aqueous and blood-retinal barriers, choroidal and conjunctival blood flow, lymphatic clearance, and tear dilution). The microdevice can be a useful tool to determine what level of the drug reaches the ocular surface.
Metabolic monitoring is of great utility to environmental monitoring. Changes in the concentrations of metabolites are the precursors and products of enzymatic activity, and can be associated with biological function and regulation. Metabolic monitoring hence can be used for environmental monitoring, e.g., risk assessment of chemicals and diagnosis of diseases in wild animals. It can also be used as a tool to better understand the underlying mechanisms of action of toxic compounds in the environment.
Additional aspects and embodiments of the disclosed subject matter are illustrated in the following examples, which are provided for better understanding of the disclosed subject matter and not limitation.
Graphene Aptameric Nanaseonsor for Detection of InsulinTechniques for real-time detection of insulin using a nanosensor system are disclosed herein. The disclosed subject matter can allow real-time, label-free, and selective detection of insulin concentration.
As embodied herein, the disclosed subject matter provides a nanosensor system for detecting insulin molecules in a sample. The nanosensor system can be based on a graphene-based field-effect transistor (GFET). The field-effect transistor can include a graphene channel and an aptamer. The aptamer can be coupled to the graphene channel through a linker. The aptamer can be attached to the linker in the first conformation and convert into a second conformation when the aptamer binds to the target molecule. The graphene-based FET can provide improved response speed, specificity, and sensitivity for target detection.
In certain embodiments, the disclosed subject matter provides a graphene channel. Graphene, a monolayer of carbon arranged in a hexagonal lattice, can be located on a substrate between at least two electrodes (e.g., drain electrode and source electrode) with a gate contact. For example, graphene can be transferred onto 285 nm SiO2/Si substrate. Gate, drain, and source electrodes (Cr/Au) can be subsequently fabricated using E-beam evaporation and lift-off techniques. The graphene can be patterned to define the conducting channel using photolithography and oxygen plasma etching. In some embodiments, the graphene channel can serve as a conducting channel between the electrodes. The electrical double later at the interface of graphene and electrolytes can serve as a gate dielectric. The drain and source electrodes can be biased with voltage and generate a current through the graphene channel, as a function of applied gate voltage. Because of insulin's characteristics (e.g., molecular weight of insulin and concentration), insulin is not adsorbed to bare graphene in a few minutes (e.g., <10 min) or the adsorption does not introduce significant variation in the graphene conductivity. Therefore, graphene can be an appropriate channel for insulin detection.
In certain embodiments, the disclosed subject matter provides a linker. The linker can be coupled to the graphene channel. For example, the linker can be noncovalently coupled to the graphene channel via π-π stacking between pyrene group and graphene. The π-π stacking can refer to attractive, noncovalent interactions between aromatic rings. In some embodiments, the linker can include 1-pyrenebutanoic acid succinimidyl ester (PASE). The PASE linker can be immobilized on the surface of the graphene channel. The PASE linker can include the N-hydroxysuccinimide ester group to bind to an aptamer. In non-limiting embodiments, the coupling of PASE to graphene can increase VDirac (voltage at which the current reaches its minimum), suggesting that PASE can introduce p-type doping in graphene. The thickness of the graphene channel can be increase after functionalization with a linker and can be measured by atomic force microscopy (AFM) to confirm that the linkers are immobilized on the graphene surface.
In certain embodiments, the disclosed subject matter provides an aptamer. The aptamer can be coupled to the graphene channel through the linker. The aptamer can include DNA, RNA, XNA, and peptide aptamer. DNA, RNA, and XNA aptamers can include strands of oligonucleotides, and peptide aptamer can include one or more short variable peptide domains. In some embodiments, an aptamer can be conjugated to the linker by forming amide bone. For example, an amino group of an aptamer can be attached to the N-hydroxysuccinimide ester on PASE. To immobilize an aptamer onto the graphene channel, the graphene channel can be firstly immersed in PASE (e.g., 5 mM) solution at room temperature, sequentially rinsed with dimethylformamide (DMF) and phosphate buffered saline (PBS) buffer to remove free PASE. The graphene channel can be then rinsed with PBS followed by incubation with aptamer solution (e.g., 100 nM) for overnight at room temperature. After rinsing with PBS, ethanolamine (e.g., 100 mM) can be added onto the graphene channel to deactivate and block the excess reactive groups remaining on graphene surface. A polydimethylsiloxane (PDMS)-based open well (˜20 μL) used to hold sample solutions can be bonded to the graphene channel.
In certain embodiments, the disclosed aptamer can selectively bind to the target molecule or analyte. For example, any aptamers which selectively binds to insulin molecules can be used for the disclosed nanosensor system. The insulin-specific aptamers can include a particular core sequence which binds to the target molecule or analyte. In some embodiments, the aptamer can include an insulin-specific IGA 3 aptamer. The IGA 3 can be a functionalized guanine-rich aptamer which has a core sequence 5′-NH2-GGT GGT GGG GGG GGT TGG TAG GGT GTC TTC-3′ (SEQ ID NO: 1). In some embodiments, the IGA 3 can include a core sequence 5′-ACA GGG GTG TGG GGA CAG GGG TGT GGG G-3′ (SEQ ID NO: 2), 5′-GGA GGT GGA TGG GGA GGG GGA GGT GTG TTT-3′ (SEQ ID NO: 3), or 5′-GGA GGG GGT GGG GAG GGG GCT GGT TGT CC-3′ (SEQ ID NO: 4).
In certain embodiments, the disclosed aptamer can change its structure upon the binding of the target molecules or analytes. The aptamer can be coupled to the linker in the first confirmation. Then, the structure of the aptamer can transform into the second confirmation when the target molecules bind to the aptamer. For example, in the absence of insulin, the guanine-rich IGA3 aptamer can be unfolded in the solution while G-quartet structure can be formed as a result of Hoogsteen base pairing. Upon capture of insulin, the existing G-quartet structures can switch to stable, compact parallel or antiparallel G-quadruplex structures. These conformational changes can move the electron-rich aromatic nucleotide strands and insulin to the close proximity of the graphene surface, resulting in the direct binding of nucleotide or aromatic amino acids in insulin with the graphene surface. Such conformation can transfer electrons from either insulin or the deformed IGA3 aptamer into graphene through the π-π stacking interactions between them and generate n-type doping to graphene.
In certain embodiments, the binding of insulin to aptamer IGA3 can alter the carrier concentration in the graphene channel. The altered carrier concentration can further change a conductance of the graphene layer and Ids. In some embodiments, the conductance of the graphene layer and Ids can be measured to determine the insulin concentration. For example, the graphene aptameric nanosensor can be treated with an insulin or/and glucagon solution. During the treatment, both the drain and gate voltage can be supplied by a sourcemeter, and Ids can be simultaneously measured to determine the insulin concentration.
In certain embodiments, the disclosed subject matter can provide methods for preparing the nanosensor. The method can include cleaning the wafer surface with oxygen plasma. As shown in
In certain aspect, the disclosed FET can detect a target analyte in a sample. The sample can include ionic solutions, blood, physiological-salt concentration solutions, and high-salt concentration solutions. In some embodiments, the disclosed subject matter provides methods and systems for real time, label-free and specific detection of insulin concentrations as low as about 1 nM. For example, the graphene nanosensor can monitor insulin levels ranging from about 1 nM to about 5000 nM, about 1 nM to 4000 nM, about 1 nM to 3000 nM, about 1 nM to 2000 nM, about 1 nM to 1000 nM, about 1 nM to 500 nM, about 1 nM to 250 nM, about 1 nM to 100 nM, and about 1 nM to 50 nM in real time.
Example 1. In Vivo Testing of a MicrodeviceMicrodevices with affinity polymers such as poly(acrylamide-ran-3-acrylamidophenyl boronic acid) (PAA-ran-3PAAPBA) were tested in mice. The polymers were constructed with phenylboronic acid groups that bind with glucose at 2:1 ratio to form cyclic esters. The resulting changes in physical (e.g., viscometric and dielectric) properties of the polymer were measured with a microelectromechanical systems (MEMS) device (
The nanosensor used in this test is depicted in
CVD graphene (205) was synthesized by heating annealed Cu foil (213) in a quartz tubing furnace (
Graphene (205) was transferred onto the substrate (217) at 170° C. (
Cr/Au (5 nm/45 nm) layers (307) were deposited on the top of Si/SiO2 substrate (BOC/Auto 306 thermal evaporator, Edwards) (318) (with Photoresist (S1811, Shipley) was then spin-coated on top (319)) and patterned to create the source/drain electrodes using photolithography (MA6 Mask Aligner, Karl-Suss) and wet-chemical etches (
Microfluidic channel was fabricated using standard soft lithography (
Illustrated herein is a GFET sensor that can allow accurate detection of a target analyte (e.g., H+).
Graphene can be used to form a conducting channel in field effect transistors (FET), allowing highly sensitive electric detection of analytes. Such graphene FET (GFET) sensors, when operating in liquid media, can be generally constructed in a solution-gated or solid-gated configuration. In a solution-gated GFET sensor, a reference electrode can be inserted into the electrolyte solution that is in contact with graphene to serve as the gate electrode, while the electric double layer (EDL) formed at the solution-graphene interface can play the role of the gate dielectric. Theses solution-gated sensors typically can require an external electrode inserted into the electrolyte solution, which hinders the integration and miniaturization of the device. In addition, the gate capacitance, or the capacitance across the EDL dielectric layer can be susceptible to disturbances in liquid media, which can result in fluctuations in electrical measurements of properties of graphene including the position of the Dirac point. In contrast, in a typical solid-gated GFET, the gate capacitance can be provided by a SiO2 dielectric layer sandwiched between graphene and the underlying silicon substrate, which serves as the gate electrode. By eliminating the need for the external wire insertion into the electrolyte solution, solid-gated sensors can be highly miniaturized and integrated. However, due to the intrinsically low capacitance of the SiO2 layer, usually the solid-gated GFET sensors can require undesirably high gate voltages (40˜50 V), consequently impeding their application to biosensing in liquid media.
This example presents a GFET nanosensor in liquid media using a thin layer of HfO2 with a high dielectric constant (κ) as a gate dielectric layer (506). The HfO2 layer can be sandwiched between the conducting-channel graphene (505) and a gate electrode (507) (
The nanosensor was configured as a solid-gated FET device, in which a graphene sheet (505), serving as the conducting channel, connected the source (508) and drain electrodes (509) on a HfO2 dielectric layer (506), which in turn lies above the gate electrode (507) on the substrate (
The nanosensor (
In particular, the nanosensor was fabricated on a SiO2-coated silicon substrate (518, 519). After cleaning by piranha, 5/45 nm Cr/Au was deposited using thermal evaporation (BOC 306 Thermal Evaporator, Edward) (
Raman spectroscopy and atomic force microscopy (AFM) was first used to confirm that the graphene used to fabricate the device consisted of a single atomic layer. The Raman spectrum revealed G mode and 2D mode, which are characteristic of single-layer graphene (
The transfer characteristics of bare graphene in air was determined. IDS was measured while the solid-gate voltage VSG, which makes a major contribution to the overall gate voltage, was varied sinusoidally from −0.2 to 1.9 V. An ambipolar curve was observed; the Dirac point solid-gate voltage, or the gate voltage value at which the IDS achieves the minimum (
The nanosensor was tested for pH sensing in liquid media. Samples at various pH values (5.3 to 9.3) were prepared by mixing NaOH or HCl with phosphate buffered saline (PBS) buffer (Life Technologies, ionic strength ˜150 mM). A sample solution was incubated with our nanosensor, during which IDS values were measured while the gate voltage VBG was swept from 0.6 V to 1.6 V. VSG,DP<1.5 V at all pH levels (
It was also determined that these measurements were reproducible, with a different device of the same design yielding a closely agreeing sensitivity of 58.2 mV/pH (
There can be two possible physical processes that have been used to explain how adsorption of ions on graphene causes variations in the conductivity. The first process can involve the charging of the EDL capacitor by adsorbed ions, thereby causing variations in the potential in the solution in contact with the graphene, and therefore changing the Fermi level and carrier density of graphene, e.g., the electric field tuning. In the second process, which is known as the surface charge transfer doping, adsorbed ions serve as dopants, from which electrons can be exchanged into the bulk of the graphene. The solid-gated sensor, which avoids the influence of the externally applied top gate voltage on the EDL, can be used to investigate the effect of either the EDL capacitor charging or the surface charge transfer doping. From the transfer characteristics obtained at different pH levels (
To investigate the effect of the charging of the EDL capacitor the nanosensor was modeled as a dual-gate field effect transistor including the solid gate (with HfO2 as the dielectric) below the graphene and a solution gate formed by the EDL above the graphene at its interface with the solution. The voltage on the top solution gate, VLG, which was equal to the potential drop across the EDL capacitor, depended on the ion concentration in the electrolyte solution. This solution gate voltage, which leads to the charging of the EDL capacitor, can be estimated by the Nernst equation18, VLG−E0−2.3 log(H+)RT/nF, where E0 is a constant reference potential, R the universal gas constant, T the temperature of 298.15 K, n the ionic charge (1 for H+), F the Faraday constant. With pH=−log(H+), the following was obtained:
VLG=E0+(59.2 mV)pH (2)
Thus, the highly linear dependence of the experimentally determined VSG,DP on pH (
To demonstrate the ability of the nanosensor to perform real-time pH measurements, IDS was measured at a fixed gate voltage (VBG=0.75 V), while successively introducing samples with different pH values (
This example describes a high-κ solid-gated GFET nanosensor in liquid media. The embedded solid gate eliminates the need for an external gate electrode and is hence amenable to the complete integration of the nanosensor as is highly desirable for analyte detection in liquid media. The use of a high-κ dielectric allows the device to operate at low gate voltages and avoids errors caused by gate capacitance variations. Example data from the nanosensor showed measurements of pH in a range of 5.3 to 9.3 with a sensitivity of ˜57.6 mV/pH. The pH-dependent electrical responses of the nanosensor responsible for the measurements were found to be caused by the charging of the electric double layer capacitor, rather than surface transfer doping. These results suggest that the GFET nanosensor can be potentially used to enable highly integrated sensing of chemical and biological analytes.
Example 6. Polymer Synthesis and Graphene ImmobilizationA series of pyrene-terminated polymers were synthesized, e.g., poly(N-3-acrylamidophenylboronic acid) (pyrene-PAAPBA), using a radical addition-fragmentation chain transfer (RAFT) polymerization (
Pyrene-terminated polymers were irreversibly attached to graphene with strength comparable to covalent attachment, using a sticky point for π-π stacking interactions without disrupting the graphene's conjugation or altering its electronic properties (
This example presents a synthetic polymer-functionalized graphene nanosensor for affinity-based, label-free detection of low-molecular-weight, low-charged glucose molecules. In this sensor, graphene was functionalized with a synthetic polymer monolayer derivatized with a boronic acid group (
The nanosensor was configured as a solution-gated graphene-based FET (GFET) in that the graphene (605) was the conducting channel, formed between two gold electrodes (source (608) and drain (609)) on an insulating substrate surface (601) (
First, the polymer-glucose binding can change the position of the Dirac point (Vgs,Dirac), i.e., the value of the gate voltage at which the charge carriers neutralize and the drain-source current Ids can achieve its minimum. Cyclic esters of boronic acid can form as a result of the binding of boronic acid groups to glucose molecules, and this can cause the overall ionization equilibrium to shift from neutral/insoluble boronic acid moieties to anionic/hydrophilic boronate. Thus, the carrier density can vary because of the electron exchanges between the graphene and the solution when the charge density in the solution changes. This can alter the Fermi level of the graphene, thereby shifting the Dirac point position.
The polymer-glucose binding can also change the transconductance, gm, i.e., the drain-source current change rate with respect to the gate voltage (∂Ids/∂Vgs) in the linear region of the GEFT transfer characteristics. The charged polymer molecules lying on the graphene surface can be considered charged impurities, and induce electron scattering that degrades the carrier mobility, μ, of the graphene. This accordingly can decrease the transconductance according to:
μ=L(WCgVds)−1gm (3)
where W and L are respectively the width and length of the graphene conducting channel, and Cg is the gate capacitance per unit area.
Nanosensor FabricationThe device was fabricated using micro and nanofabrication techniques (
To perform PAAPBA polymer functionalization, the graphene and the underlying substrate were immersed in a solution of the pyrene-terminated polymer (py-PAAPBA/methanol 3% w/v) for 4 hours at room temperature, and then washed thoroughly using methanol. During testing of the nanosensor, glucose solution was placed directly above the graphene and held in a PDMS open microchannel (˜2.5 μL in volume), which was fabricated using soft lithography and reversibly bonded to the device. An Ag/AgCl reference electrode was inserted into the solution above the graphene to serve as the gate electrode for application of a gate voltage (
It was verified that single-layer graphene was used in the nanosensor via Raman spectroscopy (
The polymer functionalization of the graphene was also verified by measurement of the GFET transfer characteristics. The shape of the Ids−Vgs curve was similar before and after the functionalization protocol, while the Dirac point position Vgs,Dirac was found to have shifted from 0.22 V to 0.18 V (
The nanosensor was tested to obtain the graphene's transfer characteristics at varying glucose concentrations. It was observed that the transfer characteristics changed consistently as the binding of glucose to the boronic acid shifted the electrically neutral boronic acid groups to anionic boronate esters (
To investigate the influence of the potential contributors other than polymer-glucose binding, control measurements were performed on pristine graphene that was not functionalized with the PAPBA polymer. Neither the Dirac point position nor the transconductance changed significantly as the glucose concentration was varied from 60 to 200 mg/dL (
The device was tested for the detection of glucose in a concentration range of 0 to 200 mg/dL with a sensitivity of ˜2.5 mV/(mg/dL). These results demonstrate the potential of the device for blood glucose monitoring and control in diabetes care.
Example 8. A Graphene-Based Affinity Glucose NanosensorIn order to construct a nanosensor that can be integrated and miniaturized enough to be coupled to a contact lens, graphene, HfO2 and gold were successively laid on an SiO2-coated silicon substrate. The gold layer, lying below graphene, served as the gate, and the 20-nm HfO2 layer as the dielectric to form a solid-gated FET (
This nanosensor is built to use a mechanically flexible, CVD-prepared hexagonal boron nitride (h-BN) nanolayer to replace HfO2 (which can be brittle and not flexible) as the dielectric.
The graphene of this nanosensor can be functionalize with an optimized synthetic polymer and coupled to a contact lens-based flexible substrate.
Example 10. Preparation of a HydrogelA poly(hydroxyethyl-methacrylate) (PHEMA) based hydrogel, which has excellent biocompatibility and glucose permeability, can be synthesized in situ. A mixture of hydroxyethyl methacrylate (HEMA), tetraethyleneglycol diacrylate (TEGDA), polyethyleneglycol methacylate (PEGMA) and N-[tris(hydroxymethyl)methyl]-acrylamide (HMMA) in a ratio 86:3:5:5 mol % can be prepared, and applied to the device surfaces to form a hydrogel under UV irradiation in N2, which is then conditioned via sequential immersion in mixtures of ethanol and deionized water. The hydrogel synthesis can be optimized to enable high glucose permeability while preventing permeation of larger molecules (e.g., proteins) from tissue.
Example 11. Preparation of a Two Channel Sensor Nanosensor DesignThe graphene nanosensor design can inlcude two field-effect transistor (FET) modules of identical construction on a contact lens-based flexible substrate (
The nanosensor can be designed as summarized in the
(dG/G)/dc≈γmaxKd/[2N(Kd+c)2], (4)
where N is the graphene's charge carrier density, γmax the surface density of immobilized boronic acid groups, and Kd the equilibrium dissociation constant of the binding system. Thus, for typical material and binding properties (N ˜1015 m−2, γmax˜105 μm−2 and Kd˜10 mM)86, 87, it can be estimated that over a desired glucose concentration range of 0.5-30 mg/dL (which encompasses the hypoglycemic, normoglycemic and hyperglycemic regimes), the nanosensor sensitivity ˜0.5%-0.4%/(mg/dL). For an estimated graphene conductance measurement resolution of 0.1%, hence it is anticipated that glucose concentration can be measured at a resolution of ˜0.7-0.02%, which allows accurate affinity detection of glucose in tears.
The device's time response can be determined by the diffusive transport of glucose between the tissue and the implanted device, over a distance primarily given by the hydrogel coating (thickness ˜20-50 μm and glucose diffusivity ˜6×1011 m/s2). This can allow the device time constant to be estimated in the range of 7-42 seconds, affording a rapid response to tear glucose concentration changes.
Nanosensor FabricationTo fabricate the device, a Ti/Pd/Pt layer can be deposited onto a substrate and then covered with CVD-deposited h-BN, forming the gate electrode (107), followed by deposition and patterning of another Ti/Pd/Pt metallization as the drain (109) and source electrodes (108). A single-layer CVD graphene sheet (505) can be transferred using a protective poly(methyl methacrylate) (PMMA) layer onto the substrate and patterned to form the conducting channel. With graphene still protected by PMMA and photoresist, a thin layer (1-2 μm) of Parylene can be deposited and patterned using oxygen plasma. After dissolving the PMMA and photoresist in organic solvent, the conducting-channel graphene can be exposed and then grafted with the sensing or reference polymer, and the entire device is coated with a hydrogel. A nanosensor prototype can be fabricated on a rigid silicon substrate, and then on a flexible PET substrate. For the flexible nanosensor the device can be fabricated on a flat sheet of PET, which can then be thermally molded into a contact lens shape. PET and Parylene can be chosen for their biocompatibility as well as their excellent mechanical and chemical stability.
The nanosensor can be fabricated in a two part process with increasing complexity, first on a rigid SiO2-coated silicon substrate, and then on a flexible polymer substrate. In the case of a rigid substrate, ITO can be deposited onto a substrate and then covered with CVD-deposited h-BN, forming a transparent gate electrode. This can be followed by deposition and patterning of another ITO layer as the drain and source electrodes. A single-layer CVD graphene sheet (105) can be then transferred using a protective poly(methyl methacrylate) (PMMA) layer onto the substrate and patterned to form the conducting channel. With graphene still protected by PMMA and photoresist, a thin layer (<1 μm) of Parylene can be deposited and patterned using oxygen plasma. After dissolving the PMMA and photoresist in organic solvent, the graphene can be exposed and then grafted with the sensing or reference polymer, and the entire device is coated with a hydrogel.
Building on experience from rigid substrates, the nanosensor can be then be fabricated on a flexible substrate. To identify suitable materials to serve as the substrate for our nanosensor, materials that have been used in existing contact lens sensors can be measured, and also investigate materials commonly used in commercially available contact lenses. Contact lens-based sensors in the literature have used polymers such as polyethylene terephthalate (PET), which can be unfortunately opaque and not appropriate for practical use, and silicone. Commercially available contact lenses include “soft lenses” and “rigid lenses”. Soft lenses can be made of hydrogels or silicone-hydrogel co-polymers that have high water content but a low mechanical stiffness. In comparison, rigid lenses, with low water content, have significant stiffness to retain their shape. PMMA can be used as the substrate for fabrication of our nanosensor. Other materials include soft lens materials such as silicone (e.g., NuSil Technology MED-6015), and rigid lens materials such as silicone acrylates (e.g., Dow Corning® FA 4001 CM Silicone Acrylate) and fluorosilicone acrylates (e.g., XCEL Contacts Fluoroperm® 92).
PMMA can be the material of which the first contact lenses were made, and can be still in use in commercially available contact lenses today. It has excellent optical qualities, durability and biocompatibility, and micro- and nanofabrication techniques using PMMA are well established and have been used in our preliminary studies as a sacrificial substrate for transfer of graphene. The fabrication process described above for rigid substrates can be generally compatible with PMMA used as substrate. Using the process, the nanosensor is fabricated on a flat sheet (˜50 μm thick) of PMMA placed on a carrier silicon wafer. Upon the completion of the fabrication process, the flat PMMA sheet along with the fabricated device can then be thermally molded into the shape of a contact lens. The device could also be fabricated on suitable handling substrate (e.g., PET), and then transferred onto PMMA that has been pre-molded into a contact lens shape.
Graphene can be grafted with sensing and reference receptors (e.g., polymers), and the nanosensor can be coated with a biocompatible hydrogel.
Example 12. Understanding the Physics of Nanosensor OperationTo understand the sensing mechanisms and inform the optimal design of the graphene nanosensor, the conductance change of graphene due to polymer-glucose binding-induced changes in surface charge and compare the results with experimental data can be investigated using a simplified model in which a rectangular graphene sheet (with length l and width w) sandwiched between an insulating substrate and a solution of an electrolyte, and is biased longitudinally with a voltage without being subject to a gate voltage. The graphene surface can be charged (density: σ) due to the presence of charged (polymer and bound glucose) molecules.
The distribution can be determined of the electric potential ϕ, in the electrolyte solution near the graphene surface and then consider the charge balance at the graphene surface. While two- and three-dimensional effects (as well as those of a nonzero gate voltage) can be considered, here for simplicity it is assumed that the potential is only a function of the coordinate normal to the graphene surface (x), and that the electrolyte includes anions and cations of equal charge number z. More general cases can be considered in a conceptually similar manner. The potential distribution can be governed by the Poisson-Boltzmann equation of the form
where λ=(εkT/2z2e2c0)1/2 can be the Debye length and β=kT/ze. Here c0 is the concentration (number of molecules per unit volume) of the electrolyte in the bulk solution, ε the solution's dielectric constant, T the temperature, k the Boltzmann constant and e the electron charge. Since dϕ/dx→0 in the bulk of the solution (x→∞), the equation can be solved to obtain ϕ=−2β ln[(1+Γ0e−x/λ)/(1−Γ0e−x/λ)] where Γ0=−tan (ϕs/4β) and ϕs=ϕ(0) is the (yet-to-be-determined) potential at the graphene surface.
The charge per area induced in the graphene by the surface potential can be approximately given by σgr=Cq(ϕs−ϕ0) where ϕ0 is the surface potential at the Dirac point, and Cq is the quantum capacitance of graphene per unit area92:
Cq=(N/π)1/2e2/νfh (6)
with νf the Fermi velocity and h the Planck constant. Here N is the number of charge carriers per unit area, which depends on σgr (and hence Cq):
N=(N02+[Cq(ϕs−ϕ0)/e]2)1/2 (7)
where N0 is the sheet charge carrier concentration due to disorder and thermal excitation93.
On the graphene surface and within the graphene, conservation of charge (Gauss's law) requires that −ε0′(0)+Cqϕs=σ, i.e.,
Cq(ϕs−ϕ0)=σ−2(βε/λ)sin h(ϕs2/β) (8)
The graphene's conductance, or equivalently resistance, can then be computed from the resulting charge carrier concentration by
R=l/(μewN) (9)
where μ is the carrier mobility in graphene. Thus, the graphene resistance R can be measured to obtain the charge carrier concentration N. Then Eqs. 6, 7, and 8 can be solved to obtain the surface potential ϕs, quantum capacitance Cq, and in particular the surface charge density σ, which is directly related to surface density of the captured glucose molecules, γ. Meanwhile, the volumetric glucose concentration (c) is related to γ by the Langmuir adsorption isotherm:
γ=ξ[c/2(Kd+c)] (10)
where (as defined above) ξ is the surface density of immobilized polymer molecules and Kd the equilibrium dissociation constant of the binding system. Thus, using Eq. 10, measurement of the graphene resistance eventually allows determination of the glucose concentration c.
Example 13. In Vitro and In Vivo Characterization of the Graphene NanosensorThe polymeric materials (including PMMA, Parylene, and the synthetic functional polymer monolayers and hydrogel coating) of the nanosensor are biocompatible, as are the transducing (graphene), dielectric (h-BN) and metallization (ITO) materials when their uptake by individual cells is avoided. The in vitro characterization does thus not involve compatibility testing, and focuses on the device's response to glucose concentration changes in the absence and presence of biofouling to assess its potential for accurate glucose monitoring. Verification that the device is biocompatible in in vivo studies is conducted, where in particular issues relevant to the contact lens platform, such as oxygen and ion permeability, wettability, water content, and cytoxicity, as well as protein adsorption and biofilm formation are determined.
The nanosensor's characteristics in glucose detection can be determined by exposing the nanosensor of varying design parameters (e.g., the number of atomic layers, shape and dimensions of the graphene, molecular weight of the sensing polymer, and the thickness of the hydrogel coating) to glucose or unspecific mono- and disaccharides dissolved in buffer. Measurement of the graphene conductance in these tests can allow assessment of the specificity of the device in glucose detection. The sensitivity and dynamic range of the nanosensor can be investigated by measuring the graphene conductance at physiologically relevant concentrations (0.5-30 mg/dL), with an emphasis on hypoglycemic concentrations (below 1 mg/dL). The sensitivity can then be used along with an assessment of the intrinsic noise levels in the graphene sensor and in readout instrumentation to determine the nanosensor resolution in the glucose concentration range of interest. In addition, time-resolved data from the measurements can be used to determine the device's time response.
The characterization can be also performed under varying operating parameters including temperature, pH, ionic strength and oxygen concentrations, which can significantly influence affinity binding and graphene's electronic properties. This can also be used to evaluate the ability of the device's differential design to reject the effects of variations of these parameters during sensor operation for reliable CGM.
The nanosensor's response to glucose in the presence of simulatedbiofouling can be investigated by repeating the tests above but with the device exposed to artificial tear fluid including sodium chloride, potassium chloride, sodium bicarbonate, urea, ammonia chloride, lactic acid, pyruvic acid, citric acid, Vitamin C, albumins, γ-globulins, and lysozyme. The goal is to evaluate the effects of the accumulation of biological materials, via protein adsorption and biofilm formation, on the nanosensor performance. Adsorption of proteins to the lenses can lead to the buildup of unwanted bacteria and other materials, causing contamination and degradation of the sensor sensitivity. Protein adsorption can be monitored using fluorescence spectroscopy and labeled model proteins incubated on lens surfaces. Biofilms can be collections of microorganisms encased in a matrix that is often comprised of both bacterial and host materials. The ability of microorganisms to attach to abiotic surfaces and to grow in highly stable communities greatly confounds devices that have direct contact with tissue. On the contact lens sensor, the microorganism community can form a barrier between tear and sensor, preventing detection of glucose. The attachment of biofilms to lens surfaces can be monitored using scanning electron microscopy methods while measuring the sensor response under simulated biofouling by incubating the device in bacterial cell suspension.
Affinity sensing, based on non-reactive equilibrium binding of analyte with an affinity receptor, neither consumes the target analyte nor produces any byproduct, therefore can potentially be implanted for stable and accurate glucose monitoring. Affinity glucose sensing can be implemented using optical, mechanical, and electrical methods on conventional or microscale platforms. While demonstrating the potential of affinity glucose sensing, these methods can require complex sensor structures (e.g., moving mechanical components or physical barriers), and cannot have sufficient sensitivity in human bodily fluids such as tears or saliva, in which glucose concentrations are one or two orders of magnitude lower than that in. Conventional techniques for affinity glucose sensing using functional nanomaterials to date has been rather scarce. Boron-doped graphene quantum dots have been used for affinity glucose sensing, although its requirement of an additional optical measurement system is not amenable to miniaturization. Boronic acid functionalized carbon nanotubes (CNTs) have also been used for glucose detection in deionized water. Nevertheless, these sensors relied on the contact among the randomly distributed, entangled nanotubes and is not necessarily well suited to practical applications because of a lack of consistency and stability. Furthermore, the underlying sensing mechanisms have not been clarified due to the difficulties in precise determination of the weak doping induced by the affinity binding in the semiconducting CNTs.
The disclosed subject matter provides an atomically thin, graphene-based sensor for affinity-based detection of glucose, an uncharged, low-molecular-weight molecule. The disclosed nanosensor can include a graphene FET in which graphene can be functionalized with boronic acid for glucose recognition. In contrast to a multi-step chemical modification procedure that is required for certain enzyme based graphene glucose sensors, the functionalization in the disclosed sensor can be enabled by a simple single procedure method via the interaction of graphene with pyrene-terminated boronic acid. The disclosed method can allow boronic acid to be closely attached to the graphene surface, thereby the binding of boronic acid with glucose can significantly change the electrical properties of graphene, and can enable sensitive detection of the glucose molecules. Moreover, the bipolar transfer characteristics of graphene, due to its vanishing bandgap and high mobility, can exhibit significant and definitive shifts upon glucose-boronic acid binding. This shift can reflect affinity binding-induced charge transfer to graphene, or changes in the electrostatic potential in the immediate proximity of graphene, thereby allowing for insights into the underlying physicochemical mechanisms for affinity glucose recognition on the nanomaterial. The coupling of graphene with boronic acid via stable chemical bonding can eliminate the need for mechanical movable structures or physical barriers used in existing affinity glucose sensors. Accordingly, the disclosed subject matter can simplify the device design and potentially enable a consistent, rapidly responsive measurement for noninvasive glucose monitoring. For example, wearable glucose monitoring devices can be realized by integrating these sensors with contact lens to detect the glucose concentration in tears.
The affinity glucose nanosensor was configured as a solution-gated graphene FET (
In a solution-gated FET, the capacitance of the double layer can be influenced by the solution composition. Prior to any chemical functionalization of the graphene, the fluctuations of the EDL capacitance that can possibly be attributed to changes in the glucose concentration were examined. Glucose was dissolved in phosphate buffered solution (pH 7.4) to obtain desired concentrations (2 μM to 25 mM). The same solutions were used in all of the subsequent tests. Without any chemical functionalization of graphene, the transfer characteristics (source-drain current IDS as a function of gate voltage VGS) measured at the different glucose concentrations were almost indistinguishable (
This device was then immersed in PBA solution for 4 hours at room temperature, followed by sequentially rinsing in acetonitrile, isopropanol and deionized water to remove free PBA. In prior to the chemical functionalization, in the Raman spectrum (
After functionalization, it was confirmed that replenishment of sample solution to the nanosensor did not interrupt the pyrene-graphene coupling. Then the sensor was tested by exposure to glucose solution at different concentrations. The transfer characteristics curve was found to shift to the left significantly. For example, the shift was ˜0.115 V as the glucose concentration increased from 0 to 25 mM (
The change of VNP before and after PBA functionalization was measured, denoted as ΔVNP,B, and the further changes of VNP after the graphene was exposed to glucose, denoted ΔVNP,G. Here, ΔVNP,B equals VNP,B−VNP,P, and ΔVNP,G=VNP,B−VNP,G, where VNP,P and the VNP,B are the neutral point voltages measured in fresh buffer for pristine graphene and PBA-functionalized graphene, respectively. VNP,G is the neutral point voltage for PBA-functionalized graphene measured in glucose solution. Both ΔVNP,B and ΔVNP,G were observed to vary from device to device, possibly because of artifacts such as organic residue left on graphene from the fabrication process. These artifacts could have caused a device-to-device disparity in chemical functionalization of graphene, and hence in the doping level at a given glucose concentration. At a given concentration, the ratio ΔVNP,G/ΔVNP,B did not vary significantly from device to device, with a variation of less than 6% for the three nanosensor devices tested (
While the exact mechanisms for the graphene affinity sensing remain open, some theoretical considerations can offer insight into the observed doping effects induced by chemical functionalization and glucose-boronic acid binding. First, to explain the observed p-type doping due to the attachment of PBA (
These conjectured sensing mechanisms suggest that immobilization of boronic acid on graphene or even other semiconducting materials, using other attachment groups can also allow for glucose recognition. Indeed, measurements of glucose using graphene that was modified with 9-anthracene-boronic acid were found to be qualitatively consistent with results obtained with PBA as presented above. The corroboration of these mechanisms, however, require a systematic study in future work. Although adequate for practical glucose detection in physiological fluids where glucose is present at dominant concentrations, boronic acid-based receptors can be chemically modified to impart glucose-specificity to the nanosensor over other monosaccharides.
In certain embodiments, the disclosed graphene nanosensor can perform affinity-based detection of low-charge, low-molecular-weight molecules, using glucose as a representative analyte. The nanosensor can use a graphene field-effector transistor in which graphene can be functionalized with boronic acid for glucose recognition. The boronic acid can be attached to graphene via the interaction between graphene and pyrene groups, allowing sensitive detection of electrically neutral glucose molecules. Testing results demonstrated that the nanosensor was capable of measuring glucose in a practically relevant range of 2 μM to 25 mM, with a resolution of 0.46 μM. The observed shifts of the transfer characteristics strongly suggested that recognition of glucose was due to the formation of glucose-boronate ester, which could reduce the boronic acid-induced p-type doping in the graphene. The disclosed nanosensor can be highly miniaturized without the use of mechanical moving parts or physical barriers, and hence be of practical utility in glucose monitoring.
The disclosed subject matter further provides for devices and techniques to monitor target analytes. More specifically, the disclosed subject matter provides for field-effect transistor (“FET”)-based sensors and systems that can be used with aptamers that bind to targets with high specificity and affinity.
The disclosed subject matter provides a graphene nanosensor for monitoring a target analyte. In certain embodiments, the graphene nanosensor utilizes a single conductance sensor on a substrate platform, wherein the graphene sensor can be functionalized with aptamers for binding the target analyte. In certain embodiments, the graphene nanosensor utilizes microbeads functionalized with aptamers which can allow for selective enrichment and isocratic elution of the target analyte. In certain embodiments, the concentration of the enriched target analyte can be measured on a graphene surface functionalized with a target analyte of interest.
In certain embodiments, the sensor can be made of graphene. Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional honeycomb lattice. In certain embodiments, the FET sensing element with graphene as the conducting channel has an electric resistance of about 0.1 kΩ-about 3 kΩ. In certain embodiments, graphene as the conductance channel has an electric resistance of about 0.1 kΩ-about 3 kΩ about 0.25 kΩ-about 2.75 kΩ about 0.5 kΩ-about 2.5 kΩ about 0.75 kΩ-about 2.25 kΩ about 1 kΩ-about 2 kΩ about 1.25 kΩ-about 1.75 kΩ about 1.5 kΩ-about 2 kΩ or about 2 kΩ-about 3 kΩ. In certain embodiments, graphene as the conductance channel has an electric resistance of at least about 0.1 kΩ at least about 0.2 kΩ at least about 0.3 kΩ at least about 0.4 kΩ at least about 0.5 kΩ at least about 0.6 kΩ at least about 0.7 kΩ at least about 0.8 kΩ at least about 0.9 kΩ at least about 1 kΩ at least about 1.2 kΩ at least about 1.4 kΩ at least about 1.6 kΩ at least about 1.8 kΩ at least about 2 kΩ at least about 2.2 kΩ at least about 2.4 kΩ at least about 2.6 kΩ at least about 2.8 kΩ at least about 3 kΩ at least about 4 kΩ at least about 5 kΩ at least about 6 kΩ at least about 7 kΩ at least about 8 kΩ at least about 9 kΩ or at least about 10 kΩ In certain embodiments, graphene as the conductance channel has an electric resistance of no more than about 0.1 kΩ no more than about 0.2 kΩ no more than about 0.3 kΩ no more than about 0.4 kΩ no more than about 0.5 kΩ no more than about 0.6 kΩ no more than about 0.7 kΩ no more than about 0.8 kΩ no more than about 0.9 kΩ no more than about 1 kΩ no more than about 1.2 kΩ no more than about 1.4 kΩ no more than about 1.6 kΩ no more than about 1.8 kΩ no more than about 2 kΩ no more than about 2.2 kΩ no more than about 2.4 kΩ no more than about 2.6 kΩ no more than about 2.8 kΩ no more than about 3 kΩ no more than about 4 kΩ no more than about 5 kΩ no more than about 6 kΩ no more than about 7 kΩ no more than about 8 kΩ no more than about 9 kΩ or no more than about 10 kΩ In certain embodiments, graphene as the conductance channel has an electric resistance of no more than about 3 kΩ.
The graphene monoatomic sheet can be thin (0.34 nm), possess strong mechanical strength (Young's modulus: 1 TPa), adhere to underlying substrates, and be flexible, optically transparent, and chemically stable. Such properties can enable new, transformative methods for detection of biological analytes. The monoatomic structure as well as electric conductivity (˜1738 S/m) and charge carrier mobility (2×105 cm2/Vs) of graphene can be exploited to enable sensitive analyte detection.
In certain embodiments, the graphene sensor can include a single layer sheet. In certain embodiments, the graphene sensor includes a multilayered sheet. In certain embodiments, the graphene sensor can include at least one layer of graphene. In certain embodiments, the graphene sensor can include at least two layers of graphene, at least three layers of graphene, or at least four layers of graphene. In certain embodiments, the graphene sheet can be formed by mechanical exfoliation, chemical exfoliation, chemical vapor deposition, or silicon carbide. In certain embodiments, the graphene sheet can be formed by chemical vapor deposition (“CVD”). In certain embodiments, the graphene sheet can be formed by mechanical exfoliation, which can include the removal of a layer of graphene from a block of graphite using tape or other sticky substance. Exemplary techniques for fabrication of the graphene sheet is illustrated in
In certain embodiments, the nanosensor can be constructed on a substrate platform. In using graphene as a functional material on a substrate, the nanosensors disclosed herein can be miniaturized and mechanically flexible for placement on a substrate platform. In certain embodiments, the substrate platform can be rigid. As used herein, “rigid” means self-supporting over its length when held at an edge. In certain embodiments, the substrate platform can be flexible. As used herein, “flexible” refers to a material that is not rigid and that conforms to the surface of whatever object the material contacts.
A graphene nanosensor as disclosed herein can be used in several ways. For example, binding of the target analyte with the aptamer immobilized on graphene can cause a change in surface charge density, which can penetrate the atomically thin graphene to significantly change the graphene's conductance, leading to a detectable signal even at low analyte concentrations.
In certain embodiments, the nanosensor as disclosed herein can enable reliable monitoring of a target analyte in a sample. In certain embodiments, the sample can be a bodily fluid, a non-bodily fluid liquid, or a laboratory sample. In certain embodiments, the nanosensor can be used to measure the amount or change in the amount of a target analyte in a sample. For example, the nanosensor can be part of a standalone device that monitors the target analyte in a sample added to the device (e.g., a piece of lab equipment or home monitor). In certain embodiments, the bodily fluid can be tears, blood, serum, saliva, mucus, interstitial fluid, spinal fluid, intestinal fluid, amniotic fluid, lymphatic fluid, pericardial fluid, peritoneal fluid, pleural fluid, semen, vaginal secretions, sweat, or synovial fluid of the subject.
The disclosed method can be applied to the diagnosis testing. For example, the development of nanosensing systems can be used to detect analytes, such as the presence of organics, peptides, proteins, cells, tissues, or the like in a sample. For example, but not by way of limitation, the target analyte can be immunoglobulin molecules (e.g., IgA, IgD, IgE, IgG, IgM), hormones (e.g., AVP, ADH, glucagon, amylin, GIP, GLP, epinephrine, cortisol, and growth hormone, estrogens (e.g., estradiol, strone, estriol), calcitriol, progesterone, HPL, LH, FSH, PRL, oxytocin, androgens, DHEA, DHT, orexin, EPI, MT, T3, T4, prostalandins, leukotrienes, prostacylin, thromboxane, Insulin, leptin, inhibin, PTH, somatostatin, thrombopoietin, TSH, TRH, VIP, sectetin, relaxin, renin, GnRH, GHRH, HAMP, or the like), complement factors (e.g., Complement factor C3, complement factor C4A (Anaphylatoxin) complement factor C9, complement factor D (CFAD), or the like), enzymes (e.g., lysozyme, carboxypeptidase N, pancreatic trypsin inhibitor, enzyme inhibitors: cystatin C, plasminogen, a-2-antiplasmin, inter-a-trypsin inhibitor complex component II (ITI2), a-1-antitrypsin, hexokinase type II, ribonuclease, or the like), transport proteins (e.g., transthyretin, serotransferrin, retinol binding protein (RBP), transforming growth factor-binding protein (TGF-BP), insulinlike growth factor-binding protein (IBP3), or the like), or plasma proteins (e.g., albumin, fibrinogen A (RGD Peptides), fibrinogen B, a-1-microglobulin, b-2-microglobulin, zinc-a-2-glycoprotein (ZAG), a-2-HS-glycoprotein (fetuin), serum amyloid A protein (SAA), haptoglobin, profilin, vitronectin, desmocollin, thymosin b4, apolipoprotein uteroglobin, ubiquitin, gelsolin, somatomedin B, hemopexin, or the like), oligo nucleotides, glucose.
The disclosed method can be applied to the diagnosis of disease, for example, to detect analytes, such as human viruses and bacteria, as many of those microorganisms carry glycoproteins on the exterior surface that can be targeted by the aptamers. Additionally, the disclosed techniques can be applied to a noninvasive method for monitoring cancer treatment. For example, aptamers can be designed to bind to target analytes associated with the cancer cell itself. In certain embodiments, the aptamers can be specific for apoptosis of the cancer cells. In certain embodiments, the microdevice can be used to track overall cell apoptosis to monitor when levels of cell death before they become too toxic. In certain embodiments, the microdevice is able to detect the level of cancer cells in the bodily fluid.
Furthermore, the methods disclosed herein can be used for determining the drug distribution of a treatment regimen in order to maximize the therapeutic effects of the drug. In such methods, the aptamers of the device can be designed to bind to the drug found in the bodily fluid. The design parameters can be varied without departing from the scope of the disclosed subject matter. Such design parameters include, for example, the number and dimensions of atomic layers and substrate platform layers, shape and dimensions of the graphene, and molecular weight of the aptamers, linkers, and polymers.
Aptameric Graphene NanosensorIn certain embodiments, a graphene nanosensor can utilize a single conductance sensor on a substrate platform, wherein the graphene sensor can be functionalized with aptamers for binding the target analyte. The graphene nanosensor can be functionalized with the aptamer via a linker. In certain embodiments, the nanosensor can include a nanolayer of polymer. In certain embodiments, the polymer can be conjugated to a linker attached to the graphene and also conjugated to an aptamer.
In certain embodiments, the aptamer can bind specifically to the target analyte. The aptamer can bind reversibly or irreversibly to the target analyte. The aptamer can bind to more than one target analyte. The graphene can be functionalized with at least one type of aptamer. The graphene can be functionalized with two or more types of aptamers specific for either the same or different analyte. In certain embodiments, target analyte binding with the aptamer changes the charge density on the nanosensor surface, inducing changes in the carrier concentration of the nanosensor.
With reference to
In certain embodiments, the graphene layer can be formed between the source and drain electrodes. In certain embodiments, the graphene layer lies over at least a portion of the source and drain electrodes.
In certain embodiments, the graphene surface (1101a) can be functionalized with aptamers (1105a) via π-π stacking interactions between the linker (1105b) attached to the aptamer (1105a) and the graphene surface (1101a) (
In certain embodiments, the analyte sample solution (1106) can be added above the aptamer or polymer/aptamer modified graphene in a polymeric well (1107). In certain embodiments, a wire electrode can be inserted to the solution as a gate electrode (1108). In this configuration, an electrical double layer (“EDL”) can be formed at the interface of the graphene and solution serving as the gate dielectric layer.
During operation and with reference to
The transfer characteristics of graphene can be measured in buffer by sweeping the gate voltage. A bias drain-source voltage (Vds) can be applied between the drain (1103) and source (1102) electrodes which can generate a drain-source current (Ids) through the graphene channel, and the Ids can be controlled by the applied gate voltage (Vg). This can yield the transfer characteristics of the GFET (i.e., the functional dependence of Ids on Vg). When the target analyte (1109) in a sample (1106) can be captured by the aptamer (1105a), the charged target analyte can alter the carrier concentration of the graphene (1101), and thus induce a shift of the Dirac point (VDirac), the voltage at which the Ids reaches its minimum.
In certain embodiments, the electrode wire/gate electrode can be, for example, but not limited to ITO, Ti/Pd/Pt, Ag/AgCl, Ag, Pt, Cu, Cr, or combinations thereof.
In certain embodiments, the source and drain electrodes, can be separately made from material such as, but not limited to ITO, Ti/Pd/Pt, Ag/AgCl, Ag, Pt, Cu, Cr, or combinations thereof.
In certain embodiments, the polymeric well can be made of a silicone substance, such as a polymeric organosilicon compound. In certain embodiments, the polymeric organosilicon compound can be polydimethylsiloxane (“PDMS”).
In certain embodiments, the substrate support can be made from material such as, but not limited to polyethylene terephthalate (“PET”), polycarbonate polystyrene, polymethyl methacrylate (“PMMA”), polymacon, silicones, SiO2, SiO2-coated silicon wafer, fluoropolymers, silicone acrylate, fluoro-silicone/acrylate, poly hydroxyethyl methacrylate, HfO2, parylene, Si3N4, or combinations thereof.
In certain embodiments, the dimensions of the graphene conducting channel can be a length of about 10 μm to about 20 μm by a width of about 10 μm to about 20 μm by a thickness of the graphene layer. In certain embodiments, the graphene conducting channel can have a length of about 5 μm to about 15 μm, about 7.5 μm to about 22.5 μm, about 10 μm to about 20 μm, or about 12.5 μm to about 17.5 μm. In certain embodiments, the graphene conducting channel can have a width of about 5 μm to about 15 μm, about 7.5 μm to about 22.5 μm, about 10 μm to about 20 μm, or about 12.5 μm to about 17.5 μm. In certain embodiments, the graphene channel in the sensor can be about 20×10 μm2 with a thickness of about 0.34 nm.
Exemplary techniques for fabrication of the devices is illustrated in, for example,
With reference to
With reference to
In certain embodiments, the aptamer can be attached directly to the linker. For example, the aptamer can be an amino group-terminated aptamer which can be directly attached to the linker by forming an amid bond with the carboxylic group on the linker.
Graphene Nanosensor with Integrated Selective EnrichmentIn certain embodiments, the graphene nanosensor can utilize microbeads functionalized with aptamers. In certain embodiments, aptamers which can allow for selective enrichment and isocratic elution of the target analyte. In certain embodiments, the aptamer can bind specifically to the target analyte. In certain embodiments, the aptamer can bind reversibly to the target analyte. In certain embodiments, the concentration of the enriched target analyte can be measured on a graphene surface functionalized with a target analyte of interest.
In certain embodiments, the microbeads can be functionalized with at least one type of aptamer. In certain embodiments, the graphene nanosensors can use at least one set of microbeads functionalized with one type of aptamer. In certain embodiments, the graphene nanosensors can use at least two sets of microbeads, where each set of microbeads can be functionalized with a different set of aptamers specific for either the same or different analyte.
In certain embodiments, the nanosensor can be configured as a FET in that the graphene (1501) can be the conducting channel, which is formed between two electrodes (source (1502) and drain (1503)) on an graphene nanosensor substrate platform (1504) (
In certain embodiments, the integrated microdevice can include at least one enrichment microchamber (1505), at least one graphene-based sensing microchamber (1506) combined with at least one graphene nanosensor (1501), at least three temperature control units (1507), and at least one flow gate (1508) connected to at least one serpentine channel (1509) for sample (1510) transfer to the sensing microchamber (1506). As used herein, a serpentine channel can include a channel with several segments that alternate in direction. In certain embodiments, the channels can have at least 4, at least 6, at least 8, or at least 10 alternating sections. In certain embodiments, the channel can be a straight channel. In certain embodiments, a weir structure (1511) in the at least one enrichment microchamber (1505) can retain microbeads (1512) within the enrichment microchamber (1505) during the selective enrichment process. A magnet can hold the microbeads in the enrichment microchamber (1505).
In certain embodiments, the microdevice can include at least three temperature control units (1507) which can include a resistive heater (1513) and a temperature sensor (1514) separately control temperatures inside the at least one enrichment (1505 (heater 1513a; sensor 1514a)) and sensing (1506 (heater 1513b; sensor 1514b)) microchambers and the at least one serpentine channel (1509 (heater 1513c; sensor 1514c)) for forming or disrupting aptamer-target analyte complexes. The microchambers (1505 and 1506) and the channels (e.g., 1509) can be formed by a polymeric material (516). In certain embodiments, the polymeric material can also include at least one buffer/sample inlet (1518), at least one waste outlet (1519), and at least one sample outlet (1520). In certain embodiments, the microdevice can be formed on a support platform (1517). In certain embodiments, an inlet (1518) can be coupled to the enrichment chamber, a waste outlet (1519) can be coupled to the serpentine channel, and a sample outlet (1520) can be coupled to the sensing chamber.
In certain embodiments, the microdevice can have at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, or at least 10 enrichment chambers. In certain embodiments, each enrichment chamber can have its own separate temperature control unit.
In certain embodiments, the microdevice can have at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, or at least 10 sensing chambers. In certain embodiments, there can be a sensing chamber for each enrichment chamber. In certain embodiments, there can be two sensing chambers for each enrichment chamber. In certain embodiments, each sensing chamber can have its own separate temperature control unit. In certain embodiments, valves (e.g., pneumatic) can control the movement of the sample and/or buffer to the different chambers.
In certain embodiments, the dimensions of the enrichment chamber can be a length of about 1 mm to about 5 mm by a width of about 1 mm to about 5 mm by a height of about 100 μm to about 1 mm. In certain embodiments, the enrichment chamber can be a length of about 2 mm by a width of about 2 mm by a height of about 200 μm. In certain embodiments, the length can be from about 1.25 mm to about 4.75 mm, about 1.5 mm to about 4.5 mm, about 1.75 mm to about 4.25 mm, about 2 mm to about 4 mm, or about 2.25 to about 3.75 mm. In certain embodiments, the width can be from about 1.25 mm to about 4.75 mm, about 1.5 mm to about 4.5 mm, about 1.75 mm to about 4.25 mm, about 2 mm to about 4 mm, or about 2.25 to about 3.75 mm. In certain embodiments, the height can be from about 200 μm to about 900 about 300 μm to about 800 about 400 μm to about 700 or about 500 μm to about 600 μm.
In certain embodiments, the enrichment chamber can have a volume of about 0.1 μl to about 25 μl. In certain embodiments, the enrichment chamber can have a volume of about 0.5 μl to about 20 μl, about 1 μl to about 15 μl, or about 5 μl to about 10 μl. In certain embodiments, the enrichment chamber can have a volume of about 0.1 μl to about 1 μl, about 0.2 μl to about 0.9 μl, about 0.3 μl to about 0.8 μl, about 0.4 μl to about 0.7 μl, or about 0.5 μl to about 0.6 μl.
In certain embodiments, the dimensions of the sensing chamber can be a length of about 2 mm to about 5 mm by a width of about 2 mm to about 5 mm by a height of about 1 mm to about 3 mm. In certain embodiments, the dimensions of the sensing chamber can be a length of about 2.25 mm to about 4.75 mm, about 2.5 mm to about 4.5 mm, about 2.75 to about 4.25, about 3 mm to about 4 mm, or about 3.25 mm to about 3.75 mm. In certain embodiments, the dimensions of the sensing chamber can be a width of about 2.25 mm to about 4.75 mm, about 2.5 mm to about 4.5 mm, about 2.75 to about 4.25, about 3 mm to about 4 mm, or about 3.25 mm to about 3.75 mm. In certain embodiments, the dimensions of the sensing chamber can be a height of about 1.25 mm to about 2.75 mm, about 1.5 mm to about 2.5 mm, or about 1.75 mm to about 2.25 mm. In certain embodiments, the sensing chamber can be a length of about 2 mm by a width of about 2 mm by a height of about 1 mm.
In certain embodiments, the sensing chamber can have a volume of about 4 μl to about 7 μl. In certain embodiments, the sensing chamber can have a volume of about 4.25 μl to about 6.75 μl, about 4.5 μl to about 6.5 μl, about 4.75 μl to about 6.25 μl, about 5 μl to about 6 μl, or about 5.25 μl to about 5.75 μl.
In certain embodiments, the dimensions of the serpentine channel can be a width of about 500 μm to about 1 mm by a height of about 20 μm to about 50 μm. In certain embodiments, the serpentine channel can be a width of about 500 μm by a height of about 20 μm. In certain embodiments, the serpentine channel can have a length of about 4 cm to about 10 cm. In certain embodiments, the dimensions of the serpentine channel can be a width of about 550 μm to about 950 about 600 μm to about 900 about 650 μm to about 850 or about 700 μm to about 800 μm. In certain embodiments, the dimensions of the serpentine channel can be a height of about 22.5 μm to about 47.5 about 25 μm to about 45 about 27.5 μm to about 42.5 about 30 μm to about 40 or about 32.5 μm to about 37.5 μm. In certain embodiments, the serpentine channel can have a length of about 4.5 cm to about 9.5 cm, about 5 cm to about 9 cm, about 5.5 cm to about 8.5 cm, about 6 cm to about 8 cm, or about 6.5 cm to about 7.5 cm.
In certain embodiments, the weir structure can be from about ⅕ to about 1/20 the height of the enrichment chamber. In certain embodiments, the weir structure can be from about ⅙ to about 1/19, from about 1/7 to about 1/18, from about ⅛ to about 1/17, from about 1/9 to about 1/16, from about 1/10 to about 1/15, or from about 1/11 to about 1/14 the height of the enrichment chamber. In certain embodiments, the dimensions of the weir structure can be slightly smaller than the microbeads. In certain embodiments, the weir structure can be from about ½ to about ¼ the size of the microbeads. In certain embodiments, the weir structure can be from about 10 μm to about 70 about 20 μm to about 60 or about 30 μm to about 50 μm. In certain embodiments, the weir structure can be about 20 μm.
In certain embodiments, the microbeads can have a diameter of about 40 μm to about 90 μm, about 50 μm to about 80 μm, or about 60 μm to about 70 μm.
In certain embodiments, the gate electrode can be made from material such as, but not limited to ITO, Ti/Pd/Pt, Ag/AgCl, Ag, Pt, Cu, Cr, or combinations thereof.
In certain embodiments, the source and drain electrodes, are separately made from material such as, but not limited to ITO, Ti/Pd/Pt, Ag/AgCl, Ag, Pt, Cu, Cr, or combinations thereof.
In certain embodiments, the substrate and/or support platform can be made from material such as, but not limited to polyethylene terephthalate (“PET”), polycarbonate polystyrene, polymethyl methacrylate (“PMMA”), silicones, silicon wafers, SiO2, SiO2-coated silicon wafer, fluoropolymers, silicone acrylate, fluoro-silicone/acrylate, poly hydroxyethyl methacrylate, HfO2, parylene, Si3N4, or combinations thereof.
In certain embodiments, the polymeric material can be made of a silicone substance. In certain embodiments, the silicone substance can be a polymeric organosilicon compound. In certain embodiments, the polymeric material can be polydimethylsiloxane (“PDMS”).
In certain embodiments, the temperature control unit can be a Cr/Au or Cr/Pt resistive microheater and temperature sensor.
Exemplary techniques for fabrication of the devices are illustrated in, for example,
With reference to
The microchambers and channels can be fabricated in polymeric material (1604). The microchambers and channels can be patterned by any technique known to one skilled in the art, such as but not limited to, soft photolithography. Holes can be punched into the polymeric material to create inlets and outlets for buffer and sample (1605). The sheet can then be bonded onto a support platform on which a resistive microheater and temperature sensor was placed (e.g., patterned via photolithography) (1606). The graphene sensor chip can be stacked and bonded on the polymeric layer, while the functionalized graphene region faces the open sensing microchamber (1607).
In certain embodiments, the device can initially be rinsed with buffer (e.g., about 10 μl/min), and the sensing microchamber (e.g., 1506) can be filled with a buffer solution to measure a reference signal (Ids,ref). In certain embodiments, a sample solution containing the target analyte (1703) can be introduced into the enrichment microchamber (e.g., 1505). In certain embodiments, the sample solution can be introduced into the enrichment microchamber using a syringe, syringe pump, or peristaltic pump. In certain embodiments, the enrichment microchamber can be maintained between about 25° C. to about 60° C. using a temperature control unit (e.g., 1507a) an integrated microheater and a temperature controlled sensor) integrated on the support platform (e.g., 1517). In certain embodiments, the enrichment microchamber can be maintained at about 37° C. During this stage, the target analyte (1703) can be selectively captured by an aptamer (1704) immobilized on a microbead (1702) surface, and can be enriched by continuous sample infusion into the device.
Following the enrichment, the chamber can be rinsed with a buffer solution (e.g., about 10 μl/min) to remove the impurities (1706) at the same temperature the enrichment microchamber is held at following the introduction of the sample. In certain embodiments, the buffer enters the buffer/sample inlet (e.g., 1518) and passes out the waste outlet (e.g., 1519). In certain embodiments, the sample outlet is closed so that the waste goes through the waste outlet. For example, the sample outlet tube can be clamped or closed by other mechanical means.
After the removal of nonspecifically adsorbed target analyte, molecules, and impurities (1706), the enriched target analytes can be released at an elevated temperature and eluted with free aptamers (1707), causing isocratic elution of target analytes (1703) with the free aptamer (1707). The waste outlet can be closed, a plug (i.e., a small volume of solution, e.g., 4-75 μl). of the free aptamer (1707) solution (i.e., an aptamer solution unattached to any support) can be flowed through the enrichment microchamber at an elevated temperature. The aptamer solution can be at a concentration of about 5 nM to about 50 nM, about 10 nM to about 45 nM, about, about 15 nM to about 40 nM, about 20 nM to about 35 nM, or about 25 nM to about 30 nM.
In certain embodiments, the aptamer solution can be at a concentration of about 25 nM. In certain embodiments, the amount of aptamer solution can be about 5 μl to about 15 μl or about 7.5 μm to about 12.5 μl. The flow rate of the aptamer solution can be about 10 μl. The flow rate of the aptamer solution can be about 5 μl/min to about 15 μl/min, or about 7.5 μm/min to about 12.5 μl/min. The flow rate of the aptamer solution can be about 10 μl/min. The enrichment microchamber can be maintained at a temperature of about 25° C. to about 60° C. while the aptamer solution is introduced. The enrichment microchamber can be maintained at a temperature of about 55° C. while the aptamer solution is introduced.
The mixture of eluted sample target analytes (1703) and the free aptamer (1707) can then be transferred to the sensing microchamber (e.g., 1506). The sensing microchamber can be kept at the same temperature as the enrichment chamber when the sample was first introduced. The sensing microchamber can be maintained between about 25° C. to about 60° C. using a temperature control unit (e.g., 1507b) an integrated microheater and a temperature controlled sensor) integrated on the support platform (e.g., 1517). The sensing microchamber can be maintained at about 37° C.
In certain embodiments, the sample can be continuously infused. The sample can be continuously infused for at least about 20 minutes, at least about 30 minutes, at least about 40 minutes, at least about 50 minutes, at least about 60 minutes, at least about 70 minutes, at least about 80 minutes, at least about 90 minutes, at least about 100 minutes, at least about 110 minutes, at least about 120 minutes, at least about 130 minutes, at least about 140 minutes, at least about 150 minutes, or at least about 160 minutes. The sample can be continuously infused for at least 120 minutes. In alternative embodiments, the sample can be continuously infused for about 30 minutes to about 160 minutes, about 40 minutes to about 150 minutes, about 50 minutes to about 140 minutes, about 60 minutes to about 130 minutes, about 70 minutes to about 120 minutes, about 80 minutes to about 110 minutes, or about 90 minutes to about 100 minutes.
In certain embodiments, the binding of the free aptamers to the control target analyte immobilized on the graphene surface changes the charge density on the nanosensor surface, inducing changes in the carrier concentration of the nanosensor. In certain embodiments, the measurement circuit can use a DC power supply (e.g., E3631A, Agilent) to provide the drain voltage Vds, a function generator (e.g., 33220A, Agilent) to supply the gate voltage Vgs, and a digit multimeter (e.g., 34410A, Agilent) to measure the drain current (Ids). During the electrical measurement, Ids values (at fixed Vgs and Vds) can be automatically collected once per second for a determined period.
AptamersIn certain embodiments of the disclosed subject matter, the nanosensor can be used to determine the level of a target analyte in the body, for example small organics, peptides, proteins, cells, tissues, or the like. In certain embodiments, the aptamers that identify the target analyte can be a stable single-stranded oligonucleotide (e.g., DNA, RNA, Xeno Nucleic Acid (XNA)) or peptide that binds to a specific target analyte.
Oligonucleotide aptamers can be nucleic acid species that have been engineered through repeated rounds of in vitro selection or SELEX (systematic evolution of ligands by exponential enrichment) to bind to various molecular targets.
Peptide aptamers can include a short variable peptide domain. In certain embodiments, the variable loop length can be typically composed of ten to twenty amino acids, and the scaffold can be any protein which has good solubility and stability properties. The peptide domain can be attached at both ends to a protein scaffold. The double structural constraint can increase the binding affinity of the peptide aptamer. The double structural constraint can increase the binding affinity of the peptide aptamer to nM range. Peptide aptamer selection can be made using different systems. For example, peptide aptamer selection can occur by, but not limited to, yeast two-hybrid system, selection and combinatorial peptide libraries constructed by phage display and other surface display technologies such as mRNA display, ribosome display, bacterial display and yeast display. Peptide aptamers can also include affimers, which are small, stable proteins engineered to display peptide loops which provides a high affinity binding surface for a specific target analytes. In certain embodiments, the affimers can be low molecular weight (e.g., 12-14 kDa).
The binding between the aptamer and the analyte of interest can be irreversible or reversible. In certain embodiments, the aptamer binds reversibly to the target analyte. For example, the binding and dissociation between the target analyte and the aptamer can be an equilibrium phenomenon driven by the concentration of the analyte in the sample and/or conducting channel. The amount of the analyte bound with the aptamer depends on the concentration of the analyte in the sample and/or conducting channel.
In certain embodiments, the aptamer can be conjugated to a substance that can immobilize the aptamers on the graphene sensor and/or microbead surface (i.e., functionalized surface (e.g., graphene sensor and/or microbead).
In certain embodiments, the aptamers can be irreversibly attached to graphene with strength comparable to a covalent attachment. The linker can be a pyrene-terminated agent. The pyrene-terminated agent can be 1-pyrenebutanoic acid succinimidyl ester (“PASE”). A pyrene-terminated agent can be synthesized that can irreversibly attached to graphene using a sticky point for π-π stacking interactions without disrupting the graphene's conjugation or altering its electronic properties. The amino group-terminated aptamer can be directly attached to PASE by forming amide bond.
In certain embodiments, the aptamers can be irreversibly attached to microbead. For example, the attachment can occur using interactions between avidin-biotin or NHS ester-amine.
In certain embodiments, the nanosensor can be serially functionalized with a polymer and aptamer. The polymer can minimize the non-specific adsorption of background molecules onto the graphene. In certain embodiments, the nanosensor can have a nanolayer of polymer, and, the polymer can be polyethlene glycol (“PEG”). The PEG molecule can have a molecular mass below about 2000. In certain embodiments, the PEG molecule can have a molecular mass between about 1000 to about 2000. In certain embodiments, the PEG molecule can have a molecular mass between about 1000 to about 1500, about 1100 to about 1400, or about 1200 to about 1300. In certain embodiments, the PEG molecule can have a molecular mass between about 1500 to about 2000, about 1600 to about 1900, or about 1700 to about 1800. In certain embodiments, the PEG can be linear. In certain embodiments the PEG can be branched. In certain embodiments, the polymer can be conjugated to a linker on one end of the polymer and the aptamer to the other end of the polymer. The linkage for both can be formed by amide bonds.
In certain embodiments, in order to screen out effects not caused by the target analyte, for example, environmental factors such as temperature or other analytes, the reference chamber can include a graphene sensor that is functionalized with the linker and/or linker and polymer without the aptamer (the reference linker). The reference linker does not bind with the target analyte. In certain embodiments, the reference linker can be the same linker and/or linker and polymer used to functionalize the graphene support. Also, the reference linker could not bind or react specifically with any other substance in the sample. The reference linker and polymer could, however, respond similarly to non-target analytes and environmental conditions.
In certain embodiments, in order to screen out effects not caused by the target analyte, control testing can be carried out with a control molecule (i.e., a molecule that is not the target analyte). The graphene nanosensor can be exposed to samples spiked with various concentrations of the control molecule. The transfer characteristics can be examined to see if there is a shift introduced by non-specific binding of control molecules to the graphene surface.
Additional aspects and embodiments of the disclosed subject matter are illustrated in the following examples, which are provided for better understanding of the disclosed subject matter and not limitation.
Example 14. An Aptameric Graphene Nanosensor for Analyte DetectionIllustrated herein is an aptameric graphene nanosensor that can allow accurate detection of a target analyte (e.g., 1409). Presented is an aptameric graphene field-effect transistor (“GFET”) nanosensor for sensitive and label-free detection of biomarkers in serum. The graphene nanosensor was serially functionalized with a polyethylene glycol (“PEG”) nanolayer and an aptamer for specific detection of a target analyte and effective rejection of background molecules.
This example presents a graphene nanosensor for the detection of immunoglobulin E (“IgE”) as a representative analyte. IgE can be an antibody that plays a role in mammalian immune defense eliciting protective response including local inflammation, itching, and mucus production. The PEG reduced nonspecific adsorption of serum background molecules onto graphene. The binding of IgE with the aptamer on the surface induced changes in the carrier density and mobility in the bulk of the graphene, generating a detectable signal. Results demonstrated the specific IgE detection in serum in a physiologically relevant range of 50 pM to 35 nM. Hence this nanosensor can be utilized in clinical diagnostics.
An example graphene nanosensor (e.g., 1100) was configured as an electrolyte-gated FET where graphene (e.g., 1101) was the conducting channel, formed between drain (e.g., 1103) and source electrodes (e.g., 1102) on the SiO2 substrate platform (e.g., 1104) (
During operation, the modified graphene nanosensor (
An example device was fabricated using micro and nanofabrication techniques on an oxidized silicon wafer. After cleaning by piranha, a layer of 5/45 nm Cr/Au was deposited using thermal evaporation (e.g., 1301). A layer of photoresist was then spin-coated on top of Au layer (e.g., 1302) and baked (e.g., 1303) at 115° C. for 1 min. Photolithography was used to pattern the source and drain electrodes (e.g., 1304), and the wafer was then developed (e.g., 1305) and etched in gold (e.g., 1306) and chrome etchant (e.g., 1307) sequentially. Graphene was synthesized via chemical vapor deposition (“CVD”) substrate (see Example 15 for an example protocol) and was transferred onto the to connect the source and drain electrodes (
To achieve noncovalent functionalization of the graphene surface (e.g., 400), the GFET was immersed for 2 hours at room temperature in a dimethylformamide (“DMF”) solution of 5 mM 1-pyrenebutanoic acid succinimidyl ester (“PASE”), which serves as a linker (e.g., 1401). After rinsing thoroughly with ethanol followed by phosphate buffered saline (“PBS”) buffer (e.g., 1402), the graphene sensor was immersed in a 1 mg/mL solution of PEG (MW: 2,000) in PBS solution for 12 hours at room temperature (e.g., 404). The mixture of 1-ethyl-3-(3-dimethylaminepropyl) carbodiimide hydrochloride (EDC.HCl) and N-hydroxysulfosuccinimide (“NHS”) at pH=6 in PBS solution was used to activate carboxylic group at the free end of the PEG for 1 hour (e.g., 1405). Finally, a solution of IgE specific aptamer in PBS (concentration: 1 μM) was added to the channel of GFET for 12 hours at room temperature (e.g., 1406). A rinse is applied between each procedure.
A PDMS well (˜10 L in volume) was placed above the graphene sensing region (e.g., 107) that could be filled with a serum sample. An Ag/AgCl wire was inserted into the solution to apply the gate voltage (e.g., 1108).
In testing, serum samples with different IgE concentrations were introduced into the PDMS well (e.g., 1107) for 5 minutes and then washed with PBS buffer, and the transfer characteristics of graphene then were measured in buffer by sweeping the gate voltage.
The graphene was verified to be a single layer via Raman spectroscope (
To characterize the serial functionalization of the graphene surface with PEG and the IgE-specific aptamer, the modified graphene was exposed to a fluorescently labeled single-strand DNA probe that was complementary to the aptamer. Negligible fluorescence was observed on the PEG functionalized graphene while a strong fluorescence signal was observed on the aptamer and PEG modified graphene (
The nonspecific adsorption of background molecules to graphene was observed by measuring the transfer characteristics of the bare graphene in buffer before and after the serum incubation. After incubation of the bare graphene in serum, the Dirac point VDirac shifted to negative gate voltage by 50 mV, which can be caused by the n-doping of the background molecule adsorption to graphene surface. In contrast, the PEG modified graphene did not exhibit appreciable shift of VDirac after serum incubation. This supports that the nonspecific adsorption was inhibited by the PEG nanolayer (
To investigate the response of the graphene nanosensor at varying IgE concentrations, the nanosenor was incubated in serum samples with various IgE concentrations, and the transfer characteristics were measured. The VDirac was observed to consistently shift toward the negative gate voltage from 101 mV to 85 mV as the IgE concentration increased from 50 pM to 35 nM (
Ids=μ(W/L)CVds(Vgs−VDirac) (11)
where C is the top-gate capacitance per unit area, is the carrier mobility, W and L are respectively the width and length of the graphene channel.
To exclude the possibility of nonspecific binding and false signals, control testing was carried out with a control molecule, immunoglobulin G (IgG). The graphene nanosensor was exposed to samples spiked with various IgG concentrations. The transfer characteristic curves showed negligible shifts (
CVD graphene (11401) was synthesized by heating annealed Cu foil (11402) in a quartz tubing furnace (
Graphene (11401) was transferred onto the substrate (11406) at 170° C. (
Illustrated herein is an aptameric graphene nanosensor that can allow accurate detection of a target analyte (e.g., 1500).
This example presents an integrated microfluidic aptasensor which combined aptamer-based specific enrichment and conductance-based graphene nanosensing, allowing detection of a low charged and small biomolecule with high sensitivity. An aptamer specific to a target analyte was immobilized on microbeads for solid phase-based selective enrichment and isocratic elution of the analyte. A FET configuration was used to measure changes in graphene conductance, which were used to determine the analyte concentration. Microfluidic integration of enrichment and sensing on a single chip eliminates the need for off-chip sample handling, thus minimizing potential sample contamination or loss.
For demonstration, arginine vasopressin (AVP), a small peptide and a clinically important biomarker for septic and hemorrhagic shocks, was chosen as a target analyte. Results discussed below (e.g.
An example graphene nanosensor of a FET configuration is shown in
The source and drain electrodes were connected by graphene which served as a conducting channel. A voltage was applied to the gate electrode forming a gate voltage (Vgs) through a sample solution. In this FET configuration, the electrical conductance through graphene, which depends on the charge on the graphene surface, was measured from the drain current (Ids) at a fixed drain voltage (Vds).
The microfluidic device was fabricated as follows. Graphene was synthesized via chemical vapor deposition (see Example 15), and transferred onto gold electrodes that were fabricated on a silicon dioxide-coated silicon substrate. The graphene surface was then functionalized with AVP by incubating in 1-pyrenebutanoic acid succinimidyl ester (PASE linker, 2 mM) solution for 1 hr and AVP solution (1 μM) for 4.5 hrs, sequentially. A PDMS sheet defining microchambers and channels was fabricated via soft lithography, followed by punching through-holes which were used as inlet/outlet ports and an open chamber. The sheet was then bonded onto a glass substrate on which a resistive microheater and temperature sensor was patterned via photolithography. The graphene sensor chip was finally stacked and bonded on the PDMS layer, while the AVP-functionalized graphene region was included within the open sensing microchamber.
The principle of AVP detection in the device is schematically shown in
The device was initially rinsed with buffer (10 μl/min), and the sensing microchamber was filled with a buffer solution to measure a reference signal (Ids,ref). A sample solution (10 μl/min for 2 hrs) prepared in buffer with varying AVP concentrations was continuously introduced into the enrichment microchamber using a syringe pump (KD210P, KD Scientific Inc.) while the chamber was maintained at 37° C. using a temperature control unit (an integrated microheater and a temperature sensor controlled by LabVIEW) integrated on the bottom glass substrate. Following the enrichment, the chamber was thoroughly rinsed with a buffer solution (10 μl/min) at 37° C. After the waste outlet was closed, a plug of the free aptamer solution at 25 nM was flowed through (10 μl at 10 μl/min) the enrichment microchamber at an elevated temperature, 55° C. The mixture of eluted sample AVP and the free aptamer was then transferred to the sensing microchamber whose temperature was kept at 37° C.
The measurement circuit used a DC power supply (E3631A, Agilent) to provide the drain voltage Vds, a function generator (33220A, Agilent) to supply the gate voltage Vgs, and a digit multimeter (34410A, Agilent) to measure the drain current (Ids). During the electrical measurement, Ids values (at fixed Vgs and Vds) were automatically collected once per second for a determined period through a PC-based Lab VIEW.
The aptamer binding-induced change in graphene conductance was characterized using the graphene nanosensor. A free aptamer solution at different concentrations in the range of 0-1000 nM was incubated with the graphene nanosensor until Ids reached a saturated level (
The nanosensor was then tested with standard mixtures of the free aptamer at a fixed concentration (25 nM) and sample AVP at a varying concentration (cAVP, 1-100 nM). Results showed that δIds decreased with increasing cAVP in the range of 1-100 nM, which is attributed to a higher AVP concentration in a standard mixture causes a higher aptamer occupancy, which impeded the aptamer binding to surface-immobilized standard AVP (
The aptamer-based selective enrichment of AVP was characterized on microbead surfaces via fluorescence measurements. A TAMRA (as a fluorophore)-labeled AVP (TVP) solution at 100 pM was continuously infused into the enrichment chamber (10 μl/min) while the chamber temperature was maintained at 37° C., and the fluorescence intensity of the bead surface was measured every 15 min. It was observed that mean fluorescence intensities increased over time and saturated after 1.5 hr (
To verify the specificity of aptamer-based enrichment, integrated devices were tested with and without aptamer on microbead surfaces for AVP detection. Devices with bare beads produced higher δIds values than those with aptamer-functionalized beads (
Detection of AVP was tested at physiologically relevant picomolar concentrations (1-500 pM) using the integrated device. To account for variability caused by device-to-device variation of the graphene nanosensor, δIds was normalized with respect to δIds max, the maximum conductance change of an individual graphene nanosensor. Results showed that δIds decreased with increasing cAVP (
The presently disclosed subject matter further provides an affinity-based nanosensor. As disclosed herein, affinity binding is employed for monitoring and measuring low-charge and/or low-molecular-weight analytes. Affinity binding can be specific and reversible. In other words, affinity binding can be specific when analytes or target molecules bind with analyte-specific, or target molecule-specific receptors, which do not bind with interferents that can also come into contact with such receptor. Additionally, or alternatively, affinity binding can be reversible when the analytes and/or target molecules can be released from the receptor, as depicted in exemplary
In one aspect of the presently disclosed subject matter, a graphene-based nanosensor for affinity-based detection of low-charge molecules is provided. A low-charge molecule can be a molecule, or analyte, that is substantially uncharged, such as, for example, glucose and other sugars. Additionally, or alternatively, the graphene-based nanosensor herein disclosed can accomplish affinity-based detection of low-molecular-weight molecules. A low-molecular-weight molecule, or analyte, can be, for example and without limitation, a molecule or organic compound that can regulate a biological process with a size on the order of 10-9 m, such as glucose. By way of example, and not limitation, the nanosensor can be configured as a solution-gated graphene-based field effect transistor (GFET), as depicted in exemplary
During operation, a voltage can be applied between the drain 2103 and source 2102 electrodes to generate a current in the graphene that can be measured. A bias voltage can be applied to the gate electrode 2107. Further to the above, and as disclosed herein, when no voltage is applied to the gate electrode 2107, the resistance along the graphene microchannel 2106 can be about zero. However, when a bias voltage is applied to the gate electrode, the resistance within the microchannel 2106 can increase, and can result in a functional dependence of the drain-source current on the gate electrode voltage, which can represent the transfer characteristics of the GFET. Thus, the transfer characteristics of the GFET can be affected by glucose, or other target molecule and/or analyte, contacting and binding with the glucose-responsive polymer in the microchannel, which can be measured to determine the concentration of glucose or other target molecule and/or analyte.
For example, and without limitation, upon contacting the graphene-functionalized microchannel 2106, analytes can cause detectable changes in the electrical properties of the graphene as a result of the binding of boronic acid moieties of the polymer in
Additionally, and further to the above, due to its vanishing bandgap and high mobility, the bipolar transfer characteristics of graphene can exhibit definitive shifts upon glucose-boronic acid binding. Such shifts can reflect affinity binding-induced charge transfer to graphene, or changes in the electrostatic potential in the immediate proximity of the graphene, thereby allowing for insights into the underlying physiochemical mechanisms for affinity glucose recognition on the nanomaterial. The small size of the graphene as the transduction element can allow miniaturization of the sensor dimensions.
Additionally, and further to the above, the polymer functionalization of the graphene, as illustrated in exemplary
In another aspect of the disclosed subject matter, an affinity nanosensor can measure the concentration of low-charge target molecules or analytes and/or low-molecular-weight target molecules or analytes, such as glucose, via the dielectric response of a hydrogel embedded in a MEMS capacitive transducer. Such techniques can accomplish detection and, additionally or alternatively, monitoring of an analyte by transducing the binding of the analyte with receptors, such as functional groups, in the hydrogel to changes in the dielectric properties of the hydrogel. In this manner, for example, changes in the dielectric properties of the hydrogel can be measured using a MEMS capacitive transducer. The hydrogel-based affinity nanosensor can eliminate the irreversible consumption of the target molecules as well as the interference of electroactive species, and provide stable, nontoxic material amiable for implantation. For example, and without limitation, a hydrogel can be directly immobilized onto the surface of the transducer via in situ polymerization and can be stable over time, thereby reducing the use of a semipermeable membrane, or other mechanical barriers and moving parts otherwise required to hold glucose sensitive material, that can be found in existing sensors, including existing CGM (continuous glucose monitoring) sensors, which often results in device complexity, among other drawbacks. Further, the hydrogel-based nanosensor can employ non-reactive equilibrium binding between glucose and the synthetic hydrogel, and can avoid irreversible glucose consumption.
Additionally, and further to the above, a synthetic hydrogel-based affinity glucose sensor and a MEMS differential dielectric transducer can be integrated to create a novel, miniaturized affinity CGM (continuous glucose monitoring) device with high levels of stability and accuracy, as depicted in exemplary
Example results herein disclosed demonstrate that in a practical glucose concentration range such as for example 0-500 mg/dL and with a resolution of 0.35 mg/dL or better, the hydrogel-based affinity nanosensor of the presently disclosed subject matter can exhibit a repeatable and reversible response, and can be useful for CGM (continuing glucose monitoring).
Further details of device structure, fabrication, and operation procedures of the disclosed subject matter can be found in the following Examples, which are provided for illustration purpose only, and not for limitation.
Example 17This Example demonstrates a graphene-based affinity glucose nanosensor configured using the above-described techniques. Specifically, a synthetic polymer-functionalized graphene nanosensor for affinity-based, label-free detection of low-charge, low-molecular-weight molecules was configured. As disclosed herein, the graphene is functionalized with a synthetic polymer monolayer derivatized with a boronic acid group, which is illustrated by way of example and without limitation in
Devices of Example 17 can be configured as solution-gated graphene-based field effect transistors (GFET) whereby the graphene can be the conducting channel, formed between two gold electrodes (i.e., a source electrode and a drain electrode) on an insulating substrate surface, as shown in exemplary
During operation, under the control of a voltage applied between the gate and source electrodes (VGS), a bias voltage applied between the drain and source electrodes (VDS) can generate a current through the graphene (drain-source current, IDS) that can be measured. This yields transfer characteristics of the GFET, i.e., the functional dependence of IDS on VGS, and can allow glucose concentration to be determined due to the binding of boronic acid moieties of the polymer PAPBA, which changes the electrical properties of the graphene.
For example and without limitation, the polymer-glucose binding can change the position of the Dirac point (VGS,Dirac), or, in other words, the value of the gate voltage at which the charge carriers neutralize and the drain-source current, ID, achieves its minimum. Cyclic esters of boronic acid can form as a result of the binding of boronic acid groups to glucose molecules, which causes the overall ionization equilibrium to shift from neutral/insoluble boronic acid moieties to anionic/hydrophilic boronate. Thus, the carrier density can vary because of the electron exchanges between the graphene and the solution when the charge density in the solution changes. This can alter the Fermi level of the graphene, thereby shifting the Dirac point position.
Additionally, and further to the above, the polymer-glucose binding can also change the transconductance, gm, e.g., the drain-source current change rate with respect to the gate voltage (∂IDS/∂VGS), in the linear region of the GFET transfer characteristics. The charged polymer molecules on the graphene surface can be considered charged impurities, and induce electron scattering that can degrade the carrier mobility, μ, of the graphene. For example, and without limitation, this can decrease the transconductance according to:
μ=L(WC_gV_DS)̂(−1)g_m (12)
where W and L are respectively the width and length of the graphene conducting channel, and Cg is the gate capacitance per unit area.
As disclosed herein and further to the above, the graphene-based low-molecular-weight affinity nanosensor of Example 17 was fabricated using micro and nanofabrication methods on an oxidized silicon wafer, as illustrated in
Next, to perform PAPBA polymer functionalization in accordance with Example 17, the graphene and the underlying substrate can be immersed in a solution of pyrene-terminated polymer (py-PAPBA/methanol 3% w/v) for 4 hours at room temperature, and then washed thoroughly using methanol. Other suitable immersion times and temperatures are within the contemplated scope of Example 17. During testing of the nanosensor, described in additional detail below, glucose solution can be placed directly above the graphene and held in a PDMS open microchannel (˜2.5 μL in volume), which can be fabricated using soft lithography and reversibly bonded to the sensor device. An Ag/AgCl reference electrode 2107 can be inserted into the solution above the graphene 2101 to serve as the gate electrode for application of a gate voltage, as depicted in exemplary
Raman spectroscopy can be used to test the sensor of the instant Example. Other techniques for observing and/or determining like molecular characteristics can also be employed to test the nanosensor of the presently disclosed subject matter. As illustrated by way of example and without limitation in
Polymer functionalization of the graphene was verified using Atomic Force Microscope (AFM) imaging. As shown in the exemplary AFM images of
Testing of the graphene's transfer characteristics at varying glucose concentrations (e.g., 0 mg/dL, 50 mg/dL, 100 mg/dL, and 200 mg/dL) revealed that the transfer characteristics changed consistently as the binding of glucose to the boronic acid shifted the electrically neutral boronic acid groups to anionic boronate esters, as depicted herein at reference nos. ϕ1-ϕ4 in exemplary
The influence of potential contributors or interferents other than polymer-glucose binding was also tested in Example 17. Control measurements were performed on pristine graphene that was not functionalized with the PAPBA polymer. It was observed that neither the Dirac point position nor the transconductance changed as the glucose concentration was varied from 60 to 200 mg/dL, as depicted in exemplary
This Example demonstrates a graphene-based affinity glucose sensor configured using the above-described techniques. Specifically, an atomically thin graphene-based affinity glucose nanosensor was configured as a solution-gated graphene field effect transistor (GFET), as illustrated in exemplary
Because the capacitance of the double layer can be influenced by the solution composition in a solution-gated FET, prior to any chemical functionalization of the graphene, the fluctuations of the EDL capacitance that can be attributed to changes in the glucose concentration were examined in the instant Example. For example, and without limitation, glucose was dissolved in phosphate buffered solution (pH 7.4) to obtain desired concentrations (2 μM to 25 mM). The same solutions were used in all of the subsequent tests of the instant Example for purpose of consistency, and not limitation. Without any chemical functionalization of graphene, the transfer characteristics (source-drain current IDS as a function of gate voltage VGS) measured at the different glucose concentrations were approximately identical, as depicted in exemplary
As herein disclosed, and further to the above, the nanosensor of Example 18 was then immersed in PBA (pyrene-1-boronic acid) solution for 4 hours at room temperature, followed by sequentially rinsing in acetonitrile, isopropanol and deionized water to remove free PBA. Prior to chemical functionalization, in the Raman spectrum of the graphene, depicted in exemplary
After functionalization, it was confirmed that replenishment of sample solution to the nanosensor did not interrupt the pyrene-graphene coupling. As depicted in exemplary
Additionally, the change of VNP before and after PBA functionalization, denoted herein as ΔVNP,B, and the further changes of VNP after the graphene was exposed to glucose, denoted herein as ΔVNP,G, were further studied. As herein disclosed, ΔVNP,B=ΔVNP,B−ΔVNP,P, and ΔVNP,G=ΔVNP,B−ΔVNP,G, where ΔVNP,P and the ΔVNP,B are the neutral point voltages measured in fresh buffer for pristine graphene and PBA-functionalized graphene, respectively; ΔVNP,G is the neutral point voltage for PBA-functionalized graphene measured in glucose solution. Both ΔVNP,B and ΔVNP,G varied from sensor to sensor, e.g., because of artifacts such as organic residue left on graphene from the fabrication process. These artifacts can cause a device-to-device disparity in chemical functionalization of graphene, and hence in the doping level at a given glucose concentration. At a given concentration, it was observed, and depicted in exemplary
To explain the observed p-type doping due to the attachment of PBA, depicted in
In the instant Example, a graphene-based nanosensor for affinity-based detection of low-charge, low-molecular-weight molecules and/or analytes, such as glucose, was configured and tested. Similar analytes are within the scope of Example 18, as well as the other Examples of the presently disclosed subject matter. The nanosensor of Example 18 employed a GFET (graphene field-effect transistor) in which graphene was functionalized with boronic acid groups for glucose recognition. The boronic acid was attached to the graphene via the interaction between graphene and pyrene groups, thereby allowing sensitive detection of electrically neutral glucose molecules. Testing results from Example 18 demonstrate that the nanosensor herein disclosed can measure glucose in a practically relevant range of 2 μM to 25 mM, with a resolution of 0.46 μM. The observed shifts of the transfer characteristics strongly indicate that recognition of glucose can result from the formation of glucose-boronate ester, which can reduce the boronic acid-induced p-type doping in the graphene. For practical clinical applications, the nanosensor of Example 18, representative of the presently disclosed subject matter, without limitation, can be highly miniaturized without the use of mechanical moving parts or physical barriers, and thus of practical utility in glucose monitoring applications.
In addition to the embodiments of Examples 17 and 18, it is contemplated that graphene modified using other attachment groups, such as for example and without limitation, 9-anthracene-boronic acid, instead of PBA, can obtain consistent results.
Example 19This Example demonstrates a hydrogel-based affinity glucose nanosensor configured using the above-described techniques. Specifically, the MEMS affinity of the instant Example can include a sensor chip integrated with a hydrogel of a synthetic copolymer 505, such as, for example and without limitation, poly(N-hydroxyethyl acrylamide-ran-¬3-acrylamidophenylboronic acid) (PHEAA-ran-PAAPBA), as depicted in exemplary
To fabricate the MEMS affinity nanosensor herein disclosed in Example 19, reference can be made to exemplary
During testing of the sensor herein disclosed in Example 3, the sensor was immersed in glucose solution. The device was connected to an impedance/voltage transformation circuit 2701 driven by sinusoidal input from a function generator 2702, such as for example and without limitation, an Agilent 33220A, and as shown in exemplary
First, in testing the sensor of Example 19, the sensor's hydrogel thickness was characterized using vertical scanning interference microscopy. Other suitable methods and techniques can be used to characterize hydrogel thickness. Next, the sensor's frequency-dependent effective capacitance and effective resistance at selected glucose concentrations were tested. Further, the sensor's time response to changes in glucose concentration within 40-300 mg/dL was assessed to demonstrate the potential of the sensor for realizing real-time monitoring of glucose concentrations. Finally, the output of the sensor under physiologically relevant ranges of glucose, such as, for example and without limitation, 0-500 mg/dL, was tested to evaluate the repeatability of the device for stable CGM (continuous glucose monitoring) applications.
The frequency responses of the nanosensor of Example 19, with an 8-μm hydrogel was tested at varying bias voltage frequency, denoted herein as f, and ranging from 5-90 kHz, and glucose concentration, denoted herein as cglucose, and ranging from 40-300 mg/dL. At a given cglucose in the instant Example, the effective capacitance (C) and resistance (R) both decreased with frequency as a result of the hydrogel's dielectric relaxation, as illustrated by way of example and not limitation in
In the instant Example, the sensor can be used for CGM monitoring. The sensor can include coplanar electrodes and small hydrogel thickness. Additionally, the sensor disclosed herein permits repeatable and rapid measurements of glucose concentration. The effective capacitance (C) and effective resistance (R) both increasing monotonically with glucose concentration (cglucose) in clinically relevant glucose concentrations of 0-500 mg/dL, also demonstrating the applicability of such sensors for ISF (interstitial fluid) glucose monitoring.
Example 20This Example provides a hydrogel-based affinity sensor configured using the above-described techniques. Specifically, a MEMS affinity nanosensor can utilize a synthetic glucose-sensitive hydrogel, which can be constructed, for example and without limitation, by N-3-acrylamidophenylboronic acid (AAPBA) glucose-binding motifs, and acryl N-Hydroxyethyl acrylamide (HEAA) with a tunable hydrophilicity, and which uses tetraethyleneglycol diacrylate (TEGDA) as the cross-linker 508 and 2,2′-Azobis (2-methylpropionamidine) dihydrochloride (AAPH) as the free radical polymerization initiator. In the instant Example, when glucose 2504 binds reversibly to the phenylboronic acid moieties in the AAPBA segments to form strong cyclic boronate ester bonds, a change in the dielectric properties of the hydrogel 2501 occurs and can be measured to determine the glucose concentration.
By way of example, and not limitation, the dielectric properties of the hydrogel can be represented by the complex permittivity:
ε̂*=ε̂′−iε″ (13)
where the real permittivity ε′ represents the ability of the hydrogel to store electric energy, while the imaginary permittivity ε″ is related to the dissipation of energy. In the instant Example, when the gap between the electrodes of a parallel-plate transducer is filled with the hydrogel, as shown in exemplary
ε̂′C_x/C_0 (14)
ε̂″=1/(ωR_xC_0) (15)
where C0 can be the capacitance when the electrode gap is in vacuum. The interactions of the hydrogel with glucose as disclosed herein can cause changes in the hydrogel's composition and conformation, and thus changes in its dielectric properties ε′ and ε″. Thus, the transducer of the instant Example can experience changes in its effective capacitance Cx and effective resistance Rx, which can be measured to determine glucose concentration.
Further to the above, and as disclosed herein, the transducer of the instant Example can be enabled by MEMS technology and can use a pair of parallel electrodes (2510, 2511) sandwiching the hydrogel 2501, as shown by way of example and not limitation, in
To fabricate the exemplary MEMS capacitive transducer of the instant Example, a chrome (Cr)/gold (Au) film (5/100 nm) can be deposited by thermal evaporation and patterned to form a lower electrode 511 (500 μm×500 μm) on a SiO2-coated wafer. The patterned gold electrode can then be passivated, for example, with Parylene (1 μm). Subsequently, a sacrificial layer (5 μm), such as for example an 51818, and an additional layer of Parylene (1.5 μm) can be deposited. Another Cr/Au (5/100 nm) film can then be patterned to form the upper electrode 2510 and passivated by another Parylene layer or like chemical vapor. An SU-8 layer can then be patterned to form a channel and anti-collapse microposts 2512 between the electrodes (2510, 2511). The Parylene diaphragm can be patterned with reactive ion etching (RIE) to form perforation holes to allow glucose permeation through one or more glucose permeation holes 510a. The sacrificial photoresist layer can then be removed with acetone to release the diaphragm. Such fabrication process is illustrated by way of example without limitation in
In the instant Example, the hydrogel can be prepared in situ in the capacitive transducer. First, a mixture of the hydrogel components (AAPBA, HEAA, TEGDA, and AAPH) in solution can be deoxygenated by nitrogen gas for 30 minutes, or other such suitable time, and then injected into the sensor, filling the gap between the parallel electrodes. The sensor can then be placed in a nitrogen environment and heated for four hours at 70° C., or other such suitable time and temperature, as shown by way of example and not limitation in
The hydrogel, as herein disclosed, can be synthesize via free radical polymerization with AAPBA and HEAA monomers. An HEAA to AAPBA molar ratio can be approximately equal to 9, or approximately 10% AAPBA in all the monomers. A solution including AAPBA (1.1% w/v), HEAA (5.5% v/v), TEGDA (0.8% v/v), and AAPH (0.16% w/v) in distilled water can then be prepared for polymerization. A stock solution (0.1 M) of glucose can be prepared by dissolving D-(+)-glucose (0.9 g) in distilled water to 50 mL. In the instant Example, glucose solution at varying concentrations (40, 70, 90, 180, 300, and 500 mg/dL) can be prepared by diluting the stock solution.
During testing of the nanosensor of the instant Example, the device was placed in an acrylic test cell (2 mL in volume) filled with glucose solution, as shown in exemplary
First, the sensor of the presently disclosed subject matter of the instant Example was tested to investigate its response to different glucose concentrations under bias voltages of different frequencies, as depicted in exemplary
In the instant Example, at a given frequency, the effective capacitance of the hydrogel increased consistently with glucose concentration in the entire range tested of 0-500 mg/dL, which is reflected in the sensor's frequency response depicted in exemplary
With reference to exemplary
As described herein and further to the above, the sensor was next tested by conducting tests in triplicates to examine the ability of the sensor herein disclosed to measure glucose concentrations in a repeatable manner and with adequate sensitivity, as depicted in exemplary
Additionally, and further to the above, the response to glucose as compared to the response of potential interferents of the hydrogel-based sensor herein disclosed was tested. For example, and without limitation, nonspecific molecules exist in ISF (interstitial fluid) and can interact with boronic acid, which is the glucose sensitive component of the hydrogel of the sensors herein disclosed. Such molecules can include fructose (˜1.8 mg/dL), galactose (˜1.8 mg/dL), lactate (˜9 mg/dL), and ascorbic acid (˜1.32 mg/dL). The hydrogel-based sensor of the presently disclosed subject matter, subjected to interaction with such molecules, resulted in a response lower than the response to glucose molecules. For example, at the same concentration of 90 mg/dL, the effective capacitance change at 30 kHz due to fructose, galactose, lactate, and ascorbic acid was 17%, 38%, 32%, and 28%, respectively, as depicted in exemplary
ΔC=C−C_0 (16)
where C is the effective capacitance at a given glucose (or interferent) concentration, and C0 is the effective capacitance in the absence of glucose and interferents. Considering that the physiological concentrations of the potential interferents were about one order of magnitude lower than that of glucose, the sensor of the instant Example was determined to be sufficiently selective for measurements of glucose in interstitial fluid for CGM applications.
While boronic acid can bind to diol-containing molecules, the selective response of the sensor to glucose over the potential interferents can be attributed to the unique binding behavior between boronic acid and glucose. At a 1:1 ratio, boronic acid in fact binds more strongly to fructose than glucose. However, with a high concentration of boronic acid units, which is the case in the instant Example, boronic acid can bind with glucose at a 2:1 ratio. The 2:1 binding between glucose and boronic acid units can play a major role in the sensor response by causing additional crosslinking of the hydrogel that can lead to the augmentation of elastic resistance to electric field-induced dipole reorientation. The rather insignificant device response to the exemplary potential interferents (fructose, galactose, ascorbic acid, and lactate) can alternatively be attributed to a lack of the 2:1 binding mode.
To gain further insight into the principle and operation of the sensor herein disclosed, the role of boronic acid in glucose concentration was also tested. For example and without limitation, using hydrogels with and without AAPBA content, the dependence of the effective capacitance on glucose concentration can be obtained. Such technique is illustrated by way of example and not limitation in
Finally, the sensor of Example 20 was tested with time-resolved glucose concentration measurements to assess its ability to track glucose concentration changes in a consistent and reversible manner. For example and without limitation, the measured sensor output at 30 kHz varied from 16.5 pF at 0 mg/dL to 24.8 pF at 500 mg/dL, as depicted in exemplary
Accordingly, a hydrogel-based affinity glucose nanosensor that measures glucose concentration through dielectric transduction was provided and tested in Example 4 of the presently disclosed subject matter. The sensor can include a pair of thin-film parallel capacitive electrodes sandwiching a synthetic hydrogel. Glucose molecules permeate into the hydrogel through electrode perforations, and bind reversibly to boronic acid moieties of the hydrogel. Such binding can induce changes in the dielectric polarization behavior, and hence the complex permittivity, of the hydrogel. Thus, the effective capacitance between the electrodes, which is directly related to the real part of the complex permittivity, can be measured to determine glucose concentration. The use of an in situ polymerized hydrogel in Example 4 can simplify the design of the sensor, facilitate its miniaturization and robust operation, and can improve the tolerance of the device to biofouling, for example, when implanted subcutaneously. Testing of the sensor, herein described by way of example and not limitation, showed that the effective capacitance of the sensor, in a measurement frequency range of 1-100 kHz, responded consistently to glucose concentration changes ranging from 0 to 500 mg/dL. At a given frequency, the effective capacitance increased consistently with glucose concentration, suggesting that the affinity binding between the glucose and boronic acid moieties caused the real permittivity of the hydrogel to increase. At 30 kHz, the measurement resolution of the sensor was estimated to be 0.2, 0.12, and 0.35 mg/dL in the glucose concentration ranges of 0-40, 40-300, and 300-500 mg/dL, respectively. When subjected to time varying glucose concentration changes in the full 0-500 mg/dL range, the microsensor response was consistent and reversible. The time constant of this response was approximately 16 minutes, which can be improved by using thinner hydrogels for reduced diffusion distances.
Characterization of Biomolecules Using an Aptamer-Based Graphene NanosensorAnother aspect of the presently disclosed subject matter provides systems and methods for characterizing biomolecules using an aptamer-based graphene nanosensor.
In some embodiments, understanding binding properties of biomolecules and their dependence on environmental conditions such as temperature and ionic strength can be of great interest to basic science studies and applied pharmacology. While successful characterization of biomolecular binding properties can be performed with traditional methods (e.g., optical, electrochemical, and electromechanical characterization), the traditional approaches for binding studies commonly either require molecular labeling groups and/or involve complex sensor structure and instrumentation. By contrast, graphene nanosensors, configured as graphene field-effect transistors (FET), can be configured for biomolecular binding studies because of high carrier mobility provided by FETs, resulting in high sensitivity to charged molecules. However, traditional graphene nanosensors are typically limited to equilibrium binding measurements.
The disclosed subject matter provides systems and methods for studying biomolecular interactions under different levels of ionic strength and temperature using a microfluidic graphene FET nanosensor, which is activated by analyte-specific aptamer for target molecule recognition. The disclosed systems and methods provide label-free, direct characterization of biomolecular binding properties with a single-step electrical readout so that the potential inaccurate transductional conversions commonly found in traditional platforms, where the binding kinetics are characterized by fluorescent intensity, resonate frequency or refractive index, can be eliminated.
In some embodiments, as provided by the disclosed subject matter, graphene surface can be functionalized with molecules more easily compared to gold surface-based approaches (e.g., surface plasmon resonance and quartz crystal microbalance), which require additional steps and/or a controlled environmental condition (e.g., pH). In some embodiments, the embedded temperature microsensor can be located close to the graphene sensing region of the graphene FET nanosensor to enable accurate temperature control for temperature-dependent biomolecular interaction.
In some embodiments, binding properties of biomolecules (e.g., analytes) and their dependence on ionic strength and temperature can be characterized using a microfluidic aptameric graphene field-effect transistor (FET) nanosensor. Aptamer-immobilized graphene can be used to recognize target molecules, and the resulting changes in graphene conductance can be measured to study the binding kinetics of biomolecules. Binding properties of aptamer-protein interactions at different ionic strength and temperature can be investigated, yielding insight into the pharmacologic basis of biomolecular recognition. As illustrated by
In some embodiments, a microfluidic channel 8602 can be bound to the chip to introduce the analyte and buffer. Pyrene group terminated 1-pyrenebutanoic acid succinimidyl ester (PASE) can be coupled to graphene via—stacking, and a D17.4 aptamer can be attached to the free end of PASE by forming an amide bond. When exposed to the target analyte, captured IgE by the aptamer varies carrier concentration in the graphene 8604, yielding detectable signal. A polydimethylsiloxane (PDMS) microfluidic channel 8602 can be bound to the substrate for analyte and buffer introduction to initiate the association and dissociation. Materials such as analyte and buffers can be flowed into the microfluidic channel 8602 through inlet ports 8612 and can flow out of the microfluidic channel 8602 through outlet port 8616. An on-chip temperature sensor and a Peltier module can be used for the closed-looped temperature control. The Peltier module can be a solid-state active heat pump configured to transfer heat from one side of the module to the other side, with consumption of electrical energy, depending on the direction of the current.
In some embodiments, the graphene FET nanosensor device can include an on-chip gate electrode 8608 to eliminate the use of cumbersome external wire electrodes, allowing transition-state thermodynamic parameters to be determined simultaneously in an integrated, miniaturized manner. At the same time, the disclosed graphene FET nanosensor device can facilitate a binding study of the analytes at different ionic strength and temperatures by simply normalizing the yielded signal to fraction of aptamer bound, even though the graphene is sensitive to environment conditions. Accordingly, the disclosed systems and methods for characterizing biomolecule interaction can be robust for binding studies under different circumstances.
The disclosed nanosensor can provide for label-free, direct characterization of biomolecular binding properties with one-step electrical readout so that the potential inaccurate transductional conversions commonly found in traditional platforms, where the binding kinetics are characterized by fluorescent intensity, resonate frequency or refractive index, can be eliminated. In addition, the graphene surface can be much easier to functionalize with molecules compared with gold surface-based approaches (e.g., Surface plasmon resonance and Quartz Crystal Microbalance), which require more steps and controlled environmental condition such as pH. The disclosed nanosensor device can employ a graphene FET that enables the binding assays in a label-free manner to minimize inaccuracy in binding characterization. Label-free characterization with graphene's high sensitivity to charged molecules can provide accurate quantification of biomolecular interaction. The disclosed nanosensor device, which integrates the graphene FET and microfluidic system, can greatly miniaturize the system for binding assays.
In some embodiments, the disclosed nanosensor device can be fabricated using microfabrication and/or nanofabrication techniques on an oxidized silicon wafer. In some embodiments, thermal assisted bilayer lift-off process can be used to fabricate the electrodes. In an exemplary embodiment, after cleaning by piranha, two layers of photoresist with different reflow temperature can be spin-coated on top of substrate. In some embodiments, the source, drain and gate electrodes can be patterned through photolithography. In an exemplary embodiment, after photolithographic patterning of electrodes, a layer of 5/45 nm Cr/Au can be deposited using thermal evaporation, and the remaining resist can be completely removed by immersing the whole wafer in the remover PG. In an exemplary embodiment, the graphene synthesized via chemical vapor deposition (CVD) can be transferred onto the substrate to connect the source and drain electrodes as illustrated in
In an exemplary embodiment, to achieve noncovalent functionalization of graphene surface, the graphene FET can be immersed for 2 hours at room temperature in a dimethylformamide (DMF) solution of 5 mM 1-pyrenebutanoic acid succinimidyl ester (PASE), which can serve as a linker. After rinsing thoroughly with ethanol, phosphate buffered saline (PBS) buffer and deionized water, the graphene sensor can be immersed in a solution of D17.4 aptamer in PBS (e.g., 1 μM concentration) for 12 hours at room temperature.
In some embodiments, the utility of the disclosed graphene nanosensor device can be illustrated by characterizing the kinetics of the binding between the Immunoglobulin E (IgE) and its specific aptamer (D17.4) as a representative at different Na+ and Mg2+ ionic strength, and energetics at varying temperatures, yielding insight into the pharmacologic basis of biomolecular recognition.
In some embodiments, during the operation, the association of analytes to aptamers functionalized on the graphene surface can be initiated by introducing the analyte, and dissociation can be induced by switching to buffer when the association reached equilibrium state. In an exemplary embodiment, a binding buffer containing 2.9 mM Na2HPO4, 1 mM KH2PO4 with different salts ionic strength can be prepared to study the ion-dependent binding kinetics.
In some embodiments, temperature-dependent biomolecular interactions can be investigated by measuring the response of graphene nanosensor to the interaction of IgE-D17.4 at different temperature. Temperature control enabled by the on-chip temperature sensor and a Peltier module can be achieved by a PID control system. In an exemplary embodiment, IgE at 5 nM concentration in the buffer can be prepared. Both the IgE and buffer at 5 μL/min can be introduced into the microfluidic chamber throughout the measurement. Source-drain current (i.e., Ids) at an appropriate fixed gate voltage Vgs can be measured throughout the experiments to monitor the association and dissociation events.
The results of studies illustrated in
In some embodiments, the specific recognition of aptamers and target molecules can induce changes in the conductance of graphene, which can be measured to monitor the association and dissociation between aptamers and target molecules. Binding kinetics of IgE-D17.4 and its dependence on salt, ionic strength, and temperature, can demonstrate the capability of the disclosed graphene nanosensor to characterize the biomolecular interaction at different environmental conditions.
The foregoing merely illustrates the principles of the disclosed subject matter. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the inventors' teachings herein. Features of existing methods can be integrated into the methods of the exemplary embodiments of the disclosed subject matter or a similar method. It will thus be appreciated that those skilled in the art will be able to devise numerous methods which, although not explicitly shown or described herein, embody the principles of the disclosed subject matter and are thus within its spirit and scope.
Various publications, patents and patent application are cited herein, the contents of which are hereby incorporated by reference in their entireties.
Example 21. Real-Time Monitoring of Insulin Using a Graphene Field-Effect Transistor Aptameric NanosensorThis example illustrates methods and systems for real-time, label free and specific monitoring using a field-effect transistor, whose graphene-based channel is functionalized with a guanine-rich IGA3 aptamer.
Materials and MethodThe nanosensor was configured as a graphene-based FET (
Detection of insulin was allowed by the structural change of the insulin-specific aptamer (IGA3) when interacting with insulin (
Chemical vapor deposition graphene was grown on an annealed copper (Cu) foil (99.9%, 25 μm thick). Polydimethylsi-loxane (PDMS, SYLGARD-184) was used for the PDMS chamber. 1-Pyrenebutanoic acid succinimidyl ester (PASE), phosphate buffered saline (PBS), human insulin, human glucagon, and human somatostatin were used. Insulin-specific aptamer (IGA3, sequence 5′-NH2-GGT GGT GGG GGG GGT TGG TAG GGT GTC TTC-3′ (SEQ ID NO: 1)) was synthesized and purified by Integrated DNA Technologies.
Graphene was transferred onto 285 nm SiO2/Si substrate. Gate, drain, and source electrodes (Cr/Au) were subsequently fabricated using E-beam evaporation and lift-off techniques. The graphene was then patterned to define the conducting channel using photolithography and oxygen plasma etching.
The graphene channel was then biochemically functionalized. PASE was noncovalently coupled to graphene via π-π interaction, after which the IGA3 aptamer was immobilized on the surface via the reaction of an amine group on the aptamer with the N-hydroxysuccinimide ester on PASE.
For the GFET-based electrical measurements, both the drain and gate voltages were supplied by digital sourcemeters and the current Ids was simultaneously measured using a custom-designed Lab VIEW program.
Results and DiscussionTo examine the inertness of graphene to insulin, measurements were carried out by exposing the nanosensor to insulin solutions without prior biochemical functionalization of graphene (
Characterization of the functionalization of PASE and the aptamer was performed. The coupling of PASE to graphene was found to increase VDirac from 58.5 to 181 mV (
The nanosensor insulin measuring capabilities were subsequently tested in PBS buffer. Insulin solutions of increasing concentrations from 100 pM to 1 M were sequentially introduced to the PDMS chamber of the nanosensor. The binding of insulin to the IGA3 aptamer was allowed to reach equilibrium before the replenishment of sample solutions. After exposure to insulin, the measured VDirac decreased significantly, at a rate of ˜0.075 mV/pM within physiologically relevant insulin levels (
It was observed that the transconductance of both hole and electron conduction branches remained constant, at 40.476±0.686 S. Given that the ionic strength of the buffer did not change, the double layer capacitance was also deemed unchanged. Therefore, the carrier mobility was not expected to be varied significantly by the insulin—aptamer binding. Instead, the left shift of VDirac clearly suggested that more electrons (n-type carrier) were doped into graphene upon the interaction of insulin to the IGA3 aptamer. Typically, the detection of large biomarkers, such as proteins, using a solution-gated GFET is based on the electrostatic gating effect generated by the charged biomarkers on graphene. Under these circumstances, the charges induced in graphene were opposite to and hence in balance with the charges carried by the target molecules. In the experiments, while the insulin, whose isoelectric point (PI) is 5.8, was weakly and negatively charged at pH 7.4, n-type doping was generated in graphene upon binding of insulin to the IGA3 aptamer. Thus, the increase in the electron (n-type carrier) concentration in graphene was not considered as a result of the electrostatic gating effect but could be attributed to the direct charge transfer to graphene, from either insulin or the deformed IGA3 aptamer. Note that in the absence of insulin, the guanine-rich IGA3 was mostly unfolded in the solution while G-quartet structure could have formed as a result of Hoogsteen base pairing. Upon capture of insulin, the existing G-quartet structures can switch to stable, compact parallel or antiparallel G-quadruplex structures. These conformational changes brought the electron-rich aromatic nucleotide strands and insulin to the close proximity of the graphene surface, resulting in the direct binding of nucleotide or aromatic amino acids in insulin with the graphene surface and making electrons from either insulin or the deformed IGA3 aptamer more likely to be directly transferred into graphene through the π-π stacking interactions between them and generating n-type doping to graphene. This physical process has also been observed in the immobilization of DNA on carbon nanotubes and graphene oxide sheets and possibly serves as the underlying mechanism that allows us to measure the insulin levels.
The binding of insulin and aptamer was allowed to reach equilibrium for 10 min before the replenishment of higher concentration insulin solution. Thus, the dipping time of graphene in solutions was increased with the ongoing experiment. The slight decrease in the minimum of Ids (Ids,min,) in the transfer characteristic curve, observed in
Further, the equilibrium dissociation constant (KD) for the IGA3 aptamer and insulin with different VDirac at corresponding insulin concentrations was evaluated using the aptamer-functionalized GFETs. As shown in
where ΔVDirac,max and CINS are the saturated change of the VDirac and the concentration of insulin, respectively. KD is estimated to be 35 nM from the fitted curve shown in
Time-resolved measurements of insulin were performed on the nanosensor with fixed drain-source bias Vds=50 mV and gate bias Vg=−50 mV (
To examine the specificity of the nanosensor to insulin over other related analogues that might interfere with the detection of insulin, glucagon and somatostatin, which were secreted by the pancreatic islet alpha and delta cells, respectively, were evaluated as negative control analytes. This is because glucagon [molecular weight (MW): 3.5 kD, PI: 6.2], promoting glucose storage by the liver and together with somatostatin (MW: 1.63 kD, PI: 5.6) regulating the secretion of insulin, share similar physical properties with insulin, which can affect the sensing performance. The functionalized graphene nanosensor was first exposed to somatostatin solutions prior to the introduction of insulin. The change in Ids, denoted as ΔIds, was recorded throughout the experiment and compared as the response of the aptameric nanosensor to the given solutions. To minimize errors caused by device-to-device nonuniformity, the time-resolved selective response as the ratio of ΔIds to ΔIds,max (the maximum value of ΔIds) was calculated:
ΔIds=Ids−Ids,PBS (18)
where Ids,PBS is the Ids measured in fresh PBS buffer. With exposure to somatostatin solutions at given levels, the value of ΔIds/ΔIds,max was limited to less than 0.192, indicating that the aptameric nanosensor almost did not respond to the somatostatin solution at tested concentrations. On the contrary, the calculated ΔIds/ΔIds,max value increased and reached 1.0 at 1 M insulin with stepwise increments in the insulin concentration (
Additionally, a similar real-time monitoring control experiment was conducted with glucagon (
In view of the potential use of the disclosed nanosensor for monitoring of insulin secretion from pancreatic islet beta cells, the validity of the graphene aptameric nanosensor for insulin detection in Krebs-Ringer bicarbonate (KRB) buffer was evaluated. Considering that various cytokines in serum can influence the glucose-stimulated insulin release assays, KRB buffer is generally used instead of serum-containing media as an islet perfusion medium.48,49 However, different from pure PBS buffer, KRB buffer contains 0.1% bovine serum albumin (BSA), which is a protein used as a nutrient in cell culture. To examine the stability of the graphene nanosensor in KRB buffer, control experiments were carried out by exposing the graphene channel to insulin solutions without biochemical functionalization. The variation in VDirac was not distinguishable with increasing concentrations of insulin (0-960 nM in KRB) (
After biofunctionalization of PASE and aptamers, the graphene channel was exposed to KRB buffer and insulin solutions of increasing concentrations from 900 pM to 405 nM. After exposure to insulin, the measured VDirac negatively and dramatically shifted by 42 mV, from 0.2 to 0.158 V (
In this work, G-quadruplex conformation-switching signaling was applied as the principle for a graphene aptameric nanosensor to real-time monitor insulin. The insulin specifically binds to the surface-immobilized IGA3 aptamer, promoting and stabilizing the formations of both parallel and antiparallel G-quadruplex and subsequently varying the carrier density in the graphene channel. The resulting change in the electrical conductance of graphene was measured to determine the insulin concentration. Experimental results indicated that the graphene nanosensor used by this approach demonstrated a distinctive ability in quantitative monitoring of insulin levels ranging from 100 pM to 1 μM with a LOD down to 35 pM. Additionally, the sensing performance and the practicability of this graphene nanosensor in KRB buffer were evaluated. Hence, this approach could be used in glucose-stimulated insulin release assays and holds the potential for timely and accurate prediction of insulin doses for type 1 diabetes (T1D) patients in clinical diagnostics.
Example 22. Fabrication of an Insulin-Specific Aptamer Functionalized Field-Effect TransistorThis example illustrates methods of device fabrication, surface functionalization, and use of the functionalized field-effect transistors for sensing target molecules.
Device Fabrication ProtocolAs the fabrication protocol shown in
As shown in
To immobilize the aptamer onto the graphene channel, the sensor was first immersed in 5 mM PASE solution for 2 hours at room temperature and sequentially rinsed with dimethylformamide (DMF) to remove any free PASE. The device was then rinsed with PBS followed by incubation with 100 nM aptamer IGA3 solution overnight at room temperature. After rinsing with PBS, 100 mM ethanolamine was added onto the graphene channel for 1 h to deactivate and block the excess reactive groups remaining on the graphene surface. A polydimethylsiloxane (PDMS)-based open chamber (˜30 μL) was used to hold sample solutions and was finally bonded to the device.
To test the successful functionalization of PASE and aptamer IGA3, the graphene channels of different devices were characterized with Raman Spectrum and AFM. The G-band splitting (1626, 1628, 1626 cm−1, respectively) was observed in the Raman spectra (
As shown in
In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having other combinations of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. The foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.
It will be apparent to those skilled in the art that various modifications and variations can be made in the systems and methods of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.
Claims
1. A microdevice for monitoring a target analyte, the microdevice comprising:
- a field effect transistor comprising: a substrate; a gate electrode; and a microfluidic channel including graphene, wherein the microfluidic channel is formed between drain electrodes and source electrodes on the substrate; and
- at least one aptamer functionalized on a surface of the graphene, wherein the at least one aptamer is adapted for binding to the target analyte, and wherein binding of the target analyte to the at least one aptamer can alter the conductance of the graphene.
2. The microdevice of claim 1, wherein the microfluidic channel is bound to the substrate for analyte and buffer introduction to initiate association and dissociation of the target analyte to the at least one aptamer.
3. The microdevice of claim 1, wherein the field effect transistor further comprises a gate capacitor comprising of an electrical double layer formed at the interface of the graphene and the solution.
4. The microdevice of claim 1, wherein binding of the target analyte to the at least one aptamer causes a conformational change of the at least one aptamer, causing the target analyte to be brought into a proximity to the surface of the graphene.
5. The microdevice of claim 4, wherein the target analyte being brought into proximity to the surface of the graphene causes electrical properties of graphene to change by at least one of charge transfer and electrostatic interaction.
6. The microdevice of claim 1, further comprising at least one of an on-chip temperature sensor and a Peltier module to perform closed-looped temperature control of the microdevice.
7. The microdevice of claim 1, wherein the microdevice is configured to provide a label-free direct characterization of biomolecular binding properties with one-step electrical readout.
8. The microdevice of claim 1, wherein binding of the target analyte to the aptamer causes a carrier concentration in the graphene to be altered, resulting in a detectable signal.
9. The microdevice of claim 1, wherein the at least one aptamer is functionalized on the surface of the graphene using a linker, wherein the linker is configured to be irreversibly attached to the graphene without altering electronic properties of the graphene.
10. The microdevice of claim 9, wherein the at least one aptamer is directly attached to the linker by forming an amide bond.
11. The microdevice of claim 9, wherein the linker can be coupled to the graphene via stacking, and wherein the at least one aptamer can be attached to the free end of linker by forming an amide bond.
12. The microdevice of claim 9, wherein the linker comprises 1-pyrenebutanoic acid succinimidyl ester (PASE).
13. The microdevice of claim 1, wherein the field effect transistor further comprises a source electrode and a drain electrode, and wherein the graphene makes contact with both the source electrode and the drain electrode.
14. The microdevice of claim 1, wherein the graphene comprises a single layer sheet.
15. The microdevice of claim 1, wherein the target analyte is disassociated from the at least one aptamer by introducing a buffer to the at least one aptamer.
16. A method for monitoring a target analyte using an aptamer capable of binding to a target analyte, comprising:
- placing a nanosensor in contact with target analytes, wherein the nanosensor comprises a first conductance element functionalized with an aptamer configured to detect the target analyte and a second conductance element that is insensitive to the target analyte;
- detecting a difference, if any, in the conductance of the first and second conductance elements; and
- based on the detected difference, determining a presence of the target analyte.
17. The method of claim 16, wherein the binding of the aptamer with the target analyte causes a change in the charge density on the first conductive element surface.
18. The method of claim 16, wherein a differential measurement of the conductance of the first conductance element and the second conductive element provides for determination of the presence of the target analyte and reduces an environmental factor.
19. The method of claim 16, wherein a surface of the first conductance element is adapted for a change in charge density thereon upon the binding of the aptamer with the target analyte.
20. The method of claim 16, wherein the nanosensor is adapted for real-time detection of a target analyte concentration.
21. The method of claim 16, wherein the real-time detection is continuous over time.
22. The method of claim 20, wherein the target analyte concentration is a physiologically relevant concentration.
23. The method of claim 16, further modifying the aptamer to adjust a specificity of the nanosensor to the target analyte.
24. The method of claim 23, wherein the target analyte includes an insulin.
25. The microdevice of claim 1, wherein a specificity of the microdevice to the target analyte is adjusted by modifying the aptamer.
26. The microdevice of claim 4, wherein the conformational change of the at least one aptamer includes parallel G-quadruplex conformation and antiparallel G-quadruplex conformation.
27. The microdevice of claim 1, wherein the at least one aptamer is a guanine-rich IGA3 aptamer.
28. The microdevice of claim 12, wherein the aptamer is coupled to the PASE through a reaction of an amino group of the aptamer with N-hydroxysuccinimide ester of PASE.
29. The microdevice of claim 1, wherein the microdevice is adapted for real-time detection of changes in the target concentration.
30. The microdevice of claim 29, wherein the real-time detection is continuous over time.
Type: Application
Filed: Jun 19, 2018
Publication Date: Dec 27, 2018
Applicants: THE TRUSTEES OF COLUMBIA UNIVERSITY IN THE CITY OF NEW NEW YORK (New York, NY), Department of Anatomy and Cell Biology - Universit y of Iowa (Iowa City, IA)
Inventors: Qiao Lin (New York, NY), Yibo Zhu (New York, NY), Junyi Shang (New York, NY), Zhixing Zhang (New York, NY), Xuejun Wang (New York, NY), Jaeyoung Yang (New York, NY), Cheng Wang (New York, NY), Pavana G. Rotti (Iowa City, IA), John F. Engelhardt (Iowa City, IA), Zhuang Hao (New York, NY)
Application Number: 16/012,527
