CATHODIZED GOLD NANOPARTICLE GRAPHITE PENCIL ELECTRODE AND METHOD FOR GLUCOSE DETECTION
The cathodized gold nanoparticle graphite pencil electrode is a sensitive enzymeless electrochemical glucose sensor based on the cathodization of AuNP-GPE. Cyclic voltammetry shows that advantageously, the cathodized AuNP-GPE is able to oxidize glucose partially at low potential (around −0.27 V). Fructose and sucrose cannot be oxidized at <0.1 V, thus the glucose oxidation peak at around −0.27 V is suitable enough for selective detection of glucose in the presence of fructose and sucrose. However, the glucose oxidation peak current at around −0.27 V is much lower which should be enhanced to obtain low detection limit. The AuNP-GPE cathodization increases the oxidation peak current of glucose at around −0.27 V. The dynamic range of the sensor is in the range between 0.05 to 5.0 mM of glucose with good linearity (R2=0.999). Almost no interference effect was observed for sensing of glucose in the presence of fructose, sucrose and NaCl.
1. Field of the Invention
The present invention relates to glucose sensors, and particularly to an enzyme-free cathodized gold nanoparticle graphite pencil electrode (GPE) based glucose sensor and methods for glucose detection.
2. Description of the Related Art
Glucose is an important molecule for human, plant and other living organisms. However, the presence of lower or higher concentration of dissolved glucose in blood outside of the normal range (4.4-6.6 mM) is the symptom of diseases “Diabetes mellitus”. As a result, knowing the exact glucose level in blood is crucial for diagnosis and management of Diabetes mellitus. Moreover, glucose is used in several industries such as textile, pharmaceuticals, food industries including beverages, renewable and sustainable fuel cells, and the like. Therefore, a simple, disposable, cheap, selective and sensitive glucose sensor is required for continuous glucose monitoring.
Among the common analytical methods, the electrochemical method has been widely appreciated due to its simplicity, portability, selectivity and sensitivity. Generally, electrochemical glucose sensors are classified as either (i) enzyme base glucose sensor or (ii) nonenzymatic glucose sensor. Expensive enzyme and complicated enzyme immobilization methods are required for fabrication of enzyme based electrochemical glucose sensors. Moreover, H2O2 is produced in the enzyme base glucose sensor from glucose and the produced H2O2 is oxidized on the electrode surface to generate a signal for the glucose. Practically, for oxidation of H2O2 there is typically required a potential which is high enough to oxidize interference (e.g. fructose, sucrose, ascorbic acid, dopamine uric acid etc.) in the real sample.
To overcome those problems, a plethora of nonenzymatic glucose sensors have been developed. A nonezymatic glucose sensor depends on a direct glucose oxidation signal on the electrode surface and their selectivity depends on the oxidation potential of glucose. Nanoparticles of both transition and noble metals have been used to enhance the electrocatalytic properties of a substrate electrode toward glucose oxidation. For example, gold nanowire array electrode, gold nanoparticles (Au NPs)-modified amine-functioned mesoporous silica films on glassy carbon electrode (GCE), CoOOH nanosheet-modified cobalt electrode, bimetallic Pt-M (M=Ru and Sn) NPs on carbon nanotube (CNT)-modified GCE, Pt/Ni—Co nanowires, Pd NPs on graphene oxide, Au NPs on polypyrrole nanofibers-modified GCE, copper NPs on CNT-modified GCE, Au NP-modified nitrogen-doped diamond-like carbon electrodes, AuNP/carbon nanotubes/ionic liquid nanocomposite, and Au NP-modified indium tin oxide were used to direct oxidation of glucose.
Glucose can be partially oxidized at a bulk Au electrode or a nano gold electrode at lower potential which is required to eliminate the interferences effect for detecting glucose in a real sample. However, the signal of partial oxidation of glucose in alkaline medium at Au electrode is lower than that of full oxidation at high potential. It is known that the high signal is required to obtain low detection limit in an electrochemical sensor, and that the cathodization of an Au nanomaterial based electrode before recording an electrochemical signal can enhance the electrochemical signal of the analyte. The reasons of limited use of Au electrode for routine analysis of glucose are high price of gold, complex preparation method of nano gold or nano gold-modified electrode and low signal at low potential.
Moreover, the graphite pencil electrode (GPE) is an attractive electrode material because it is cheap, available, possesses an easy to make renewable surface, and is relatively stable. However, graphite typically shows poor electrocatalytic properties toward many electroactive molecules. The poor electrocatalytic properties of GPE should be improved to obtain a lower detection limit in electrochemical sensors.
Thus, a cathodized gold nanoparticle graphite pencil electrode addressing the aforementioned problems is desired.
SUMMARY OF THE INVENTIONEmbodiments of a cathodized gold nanoparticle graphite pencil electrode (AuNP-GPE) provide a highly sensitive enzymeless electrochemical glucose sensor that is based on the cathodized gold nanoparticle-modified graphite pencil electrode (AuNP-GPE). By combining the advantages of AuNP, GPE and cathodization, embodiments of an AuNP-GPE provide for the fabrication of a nonenzymatic highly selective and relatively sensitive, cheap and disposable glucose sensor. The AuNP-GPE after cathodization at an optimum condition shows relatively a high selectivity, a low detection limit (12 micromolar (μM)) and a wide dynamic range (0.05-5 millimolar (mM)) toward glucose sensing. The cyclic voltammetry (CV) experiments show that embodiments of an AuNP-GPE can oxidize glucose partially at low potential (around −0.27 volts (V)), whereas the bare GPE generally cannot oxidize glucose in the entire tested potential windows, and that fructose and sucrose generally cannot be oxidized at <0.1 V at an AuNP-GPE. As a result, the glucose oxidation peak at around −0.27 V is relatively suitable enough for selective detection of glucose in the presence of fructose and sucrose.
However, the glucose oxidation peak current at around −0.27 V is typically much lower which should be enhanced to obtain a low detection limit. To increase the oxidation peak current of glucose at around −0.27 V, embodiments of an AuNP-GPE have been cathodized under relatively optimum condition (−1.0 V for 30 seconds (s)) in the same glucose solution before recording cyclic voltammetry (CV). This cathodization of an AuNP-GPE enhances the glucose signal and can allow a detection limit of 12 μM of glucose, for example. The dynamic range of embodiments of a glucose sensor using embodiments of a cathodized AuNP-GPE are typically in the range between 0.05 to 5.0 mM of glucose with relatively good linearity (R2=0.999). Also, no significant interference effect was observed for the sensing of glucose in the presence of fructose, sucrose and NaCl.
These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.
Unless otherwise indicated, similar reference characters denote corresponding features consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSEmbodiments of a cathodized gold nanoparticle graphite pencil electrode (AuNP-GPE) 10b (shown in
However, the glucose oxidation peak current at around −0.27 V is much lower which should be enhanced to obtain a low detection limit. To increase the oxidation peak current of glucose at around −0.27 V, the embodiments of an AuNP-GPE have been cathodized under a relatively optimum condition (−1.0 V for 30 s) in the same glucose solution before performing and recording cyclic voltammetry (CV). This cathodization enhances the glucose signal and allows for a glucose detection limit of 12 μM, for example. The dynamic range of the sensor is in the range between 0.05 to 5.0 mM of glucose with a relatively good linearity (R2=0.999). Also, no significant interference effect was observed for sensing of glucose in the presence of fructose, sucrose and NaCl, for example.
With respect to reagents used in relation to preparation of embodiments of an AuNP-GPE, Gold(III) chloride hydrate, D-(+) Glucose, D-(−) Fructose, Sucrose, L-ascorbic acid (AA), Sodium chloride and Sodium hydroxide were received from Sigma Aldrich. As to an example of graphite used in relation to preparation of embodiments of an AuNP-GPE, hi-polymer graphite pencil HB (grade) black leads were obtained from Pentel Co. LTD. (Japan). All leads had a total length of 60 millimeters (mm) and a diameter of 0.5 mm, and were used as received. All solutions were prepared with deionized water of a resistivity of 18.6 megaohms/centimeter (MΩ/cm), which was obtained directly from PURELAB® Ultra Laboratory Water Purification System.
A Jedo mechanical pencil (Korea) was used as a holder for both bare and AuNP-modified graphite pencil leads. Electrical contact with the lead was achieved by soldering a copper wire to the metallic part that holds the lead in place inside the pencil to provide an electrically conductive holder. The pencil lead was fixed vertically with 15 mm of the pencil lead extruded outside, and 10 mm of the lead immersed in the solution. Such length corresponds to a geometric electrode area of 15.90 mm2. CH Instruments Inc. instrumentation was used for the electrochemical work in relation to embodiments of an AuNP-GPE. The electrochemical cell contained a bare GPE or an AuNP-GPE as a working electrode, a Pt wire counter electrode and Ag/AgCl (Sat. KCl) reference electrode. Before recording each voltammogram, argon gas was bubbled for 30 minutes (min) to remove oxygen from the solution. The FE-SEM images were recorded using TESCAN LYRA 3 at Center of Research Excellence in Nanotechnology (CENT), King Fahd University of Petroleum and Minerals (KFUPM), Kingdom of Saudi Arabia.
With respect to embodiments of preparation methods of an AuNP-GPE, briefly, initially equal volumes (1.5 milliliters (ml) of each aqueous solutions) of 1.65 mM AA and 1.0 mM Gold(III) chloride were mixed using a pipette at room temperature (RT) in a 3.0 ml test tube to form gold nanoparticles (AuNPs). A bare GPE was immersed into that test tube, which was placed into a water bath preheated to 75° centigrade (C) and kept for 15 min to obtain the AuNP-GPE. Afterward, the AuNP-GPE was removed and washed by gentle dipping two times in deionized water, then dried at 60° C. for 5 min prior to use. The prepared AuNP-GPE was then cathodized by placing the AuNP-GPE in a glucose analyte solution and applying −1.0 volt to the AuNP-GPE for approximately 30 seconds to provide a cathodized AuNP-GPE. Also, the prepared AuNP-GPE can also be cathodized by placing the AuNP-GPE in a basic solution, such as in a 0.1 molar (M) NaOH, at −1.0 V for 30 seconds.
With respect to electrocatalytic oxidation of glucose, fructose and sucrose, in
While the mechanism of the glucose oxidation is relatively complex, the results of the mechanism in relation to embodiments of an AuNP-GPE, indicate a glucose oxidation peak appears in an anodic sweep at around −0.27 (Epa1), and +0.27 V (Epa2)) or in a cathodic sweep around at +0.12V (Epc). Besides, the oxidation peak of fructose (the “b” line plot in
Referring to
As evident from the “b” CV plots of
With respect to optimization of cathodization parameters for glucose oxidation, to obtain a highest signal of glucose, the cathodization potential and time were optimized. Referring to
Referring to
Referring to
The reproducibility of the embodiments of glucose sensing methods using embodiments of a cathodized AuNP-GPE was verified by recording the CVs at a scan rate of 300 mV/s in a 0.1 M NaOH containing 1 mM glucose at a series of modified AuNP-GPE electrode surfaces after pretreatment at −1.0 V for 30 seconds. The intraday experiments showed a peak current of 49.128±4.7190 μA (mean±standard deviation) with a relative standard deviation of 9.6%, whereas the interday experiments showed a peak current of 49.357±4.652 μA with a relative standard deviation of 9.43%. The results indicate that embodiments of a glucose sensing method using embodiments of a cathodized AuNP-GPE are reproducible.
Regarding the effect of presence or absence of glucose during cathodization, an AuNP-GPE was cathodized in a 0.1 M NaOH containing 1 mM glucose solution, followed by recording the CV of glucose oxidation in the same solution. However, to compare the effect of glucose toward the glucose oxidation reaction if the electrode is cathodized in the absence of an analyte, the AuNP-GPE was also cathodized only in 0.1 M NaOH at −1.0 V for 30 seconds. Afterward, 1 mM equivalent amount of glucose solution was added to the 0.1 M NaOH. A comparison of the results indicates that a substantially same level of the glucose oxidation signal was obtained for both cases. These phenomena indicate that cathodization of an AuNP-GPE changes the electrocatlytic properties for the enhancing of the glucose oxidation signal, rather than the accumulation of glucose during the negative potential treatment.
Referring to
The concentration dependence calibration curve (plot 700b of
Fructose, sucrose and NaCl coexist with glucose in many samples including food and drugs. The fructose, glucose and NaCl can potentially interfere with the glucose oxidation signal. Therefore, the effects of the presence of a 1 mM fructose or sucrose or NaCl on oxidation of 1 mM glucose at embodiments of an AuNP-GPE after cathodization in the respective glucose solution at −1.0 V for 30 seconds were studied. Referring to
The “a” plot line shown in plots 800a, 800b, and 800c of
Embodiments of a cathodized AuNP-GPE provide a sensitive, selective, relatively inexpensive and disposable glucose sensor based on a cathodized AuNP-GPE. The cathodized AuNP-GPE shows relatively superior electrocatalytic properties toward electroxidation of glucose compared to an uncathodized AuNP-GPE or a bare GPE. The selectivity of the glucose sensor was obtained by selecting the appropriate potential windows of a CV. A limit of detection of the embodiments of the AuNP-GPE sensor is 12 μM of glucose, for example. For a significantly low detection limit, greater analytical selectivity and sensitivity and relatively low cost, embodiments of a method using embodiments of a cathodized AuNP-GPE based on cathodization of a relatively simply prepared AuNP-GPE can be suitable for analytical determination of glucose in various fields.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.
Claims
1-14. (canceled)
15. A method for detecting glucose, comprising the steps of:
- placing a cathodized gold nanoparticle graphite electrode (AuNP-GPE) in a glucose analyte solution; and
- performing cyclic voltammetry on the glucose analyte solution using the cathodized AuNP-GPE to detect the glucose.
16. The method for detecting glucose according to claim 15, further comprising the step of:
- using said cathodized AuNP-GPE to record cyclic voltammetry in the glucose analyte solution.
17. The method for detecting glucose according to claim 15, further comprising the step of:
- bubbling argon gas in the glucose analyte solution to remove oxygen from the glucose analyte solution.
18. The method for detecting glucose according to claim 17, wherein the argon gas is bubbled in the glucose analyte solution for approximately 30 minutes to remove oxygen from the glucose analyte solution.
Type: Application
Filed: May 22, 2015
Publication Date: Nov 19, 2015
Inventors: ABDEL-NASSER METWALLY ALY KAWDE (Dhahran), MD. ABDUL AZIZ (Dhahran)
Application Number: 14/720,066