SILICON PHOTONIC WAVEGUIDE BIOSENSOR CONFIGURATIONS
Methods and devices relating to sensors and sensor blocks for use in detecting and monitoring molecular interactions. A silicon waveguide sensing element is provided along with a layer of silicon. A silicon oxide layer is also provided between the waveguide element and the layer of silicon. The sensing element is adjacent to an aqueous solution in which the molecular interactions are occurring. A light beam travelling in the silicon waveguide creates an evanescent optical field on the surface of the sensing element adjacent to the boundary between the sensing element and the aqueous medium. Molecular interactions occurring on this surface affect the intensity or the phase of the light beam travelling through the waveguide by changing the effective refractive index of the medium. By measuring the effect on the intensity, phase, or speed of the light beam, the molecular interactions can be detected and monitored in real time. Various configurations using this sensor technology is also disclosed.
The present invention relates to sensor technology. More specifically, the present invention relates to sensors for detecting and quantifying molecular interactions by determining how much of an effect these molecular interactions have on characteristics of light passing through a waveguide adjacent an aqueous medium where these interactions are occurring.
BACKGROUND TO THE INVENTIONThe recent increase in interest in and funding for the biochemical and pharmaceutical fields has created a need for more sensitive sensors that can detect and quantify molecular interactions. The detection of these molecular interactions determine whether chemical and biological processes are at work and, as such, are key to finding new and more effective pharmaceuticals.
Unfortunately, current biosensor technology suffers from a fragility and scarcity of the equipment. Current sensor technology, such as surface plasmon resonance (SPR), is quite well-known but the equipment requires delicate handling by technicians. Furthermore, such current technologies have sensitivities that are less then desirable. With SPR, the sensitivity of the equipment is limited by the short propagation length of the plasmon.
There is therefore a need for methods and devices that mitigate if not overcome the shortcomings of the prior art.
Specifically, there is a need for techniques and devices which are easy to implement, robust, and whose sensitivity is not determined by the short propagation lengths of plasmons.
SUMMARY OF THE INVENTIONThe present invention provides methods and devices relating to sensors and sensor blocks for use in detecting and monitoring molecular interactions. A silicon waveguide sensing element is provided along with a layer of siliconA silicon oxide layer is also provided between the waveguide element and the layer of silicon. The sensing element is adjacent to an aqueous solution in which the molecular interactions are occurring. A light beam travelling in the silicon waveguide creates an evanescent optical field on the surface of the sensing element adjacent to the boundary between the sensing element and the aqueous medium.
Molecular interactions occurring on this surface affect the intensity or the phase of the light beam travelling through the waveguide by changing the effective refractive index of the medium. By measuring the effect on the intensity, phase, or speed of the light beam, the molecular interactions can be detected and monitored in real time. Various configurations in which the sensor can be used, such as in a ring resonator or a Mach-Zehnder interferometer, are also illustrated.
In one aspect, the present invention provides a sensor for use in detecting molecules in a liquid or gas medium, the sensor comprising:
-
- a substrate layer,
- a light waveguide sensor element adjacent said medium
- a lower cladding layer between said sensor element and said substrate layer
- wherein
- molecular interactions at the waveguide surface affect at least one characteristic of light travelling through said waveguide sensor element.
In another aspect, the present invention provides a method for detecting molecular interactions in a medium using a sensor having a light waveguide sensor element adjacent said aqueous medium, the method comprising:
-
- a) determining characteristics of light prior to said light entering said sensor element
- b) passing light through said sensor element
- c) determining characteristics of light after it has exited said sensor element
- d) comparing results of steps a) and c) to determine if changes in characteristics of said light occurred
- e) in the event said changes in characteristics occurred, measuring said changes
- wherein a presence of molecular interactions in said medium affect at least one characteristic of said light.
In a further aspect, the present invention provides an optical sensor block for use in detecting molecules in a liquid or gas medium, the sensor block comprising:
-
- a group of sensors comprising at least two sensor elements wherein each sensor element comprises
- a substrate layer
- a light waveguide sensor adjacent said medium
- a lower cladding layer between said waveguide sensor and said substrate layer
- wherein
- molecular interactions at the waveguide sensor surface affect at least one characteristic of light travelling through said waveguide sensor
- light travelling through said waveguide sensor is for eventual reception by an optical detector.
- a group of sensors comprising at least two sensor elements wherein each sensor element comprises
Another aspect of the invention provides an optical sensor block for use in detecting molecules in a liquid or gas medium, the sensor block comprising:
-
- a Mach-Zehnder interferometer having a first and a second arm, said first arm being a sensor arm having an optical sensor element, said optical sensor element comprising:
- a substrate layer
- a light waveguide sensor adjacent said medium
- a lower cladding layer between said waveguide sensor and said substrate layer
- wherein
- molecular interactions at the waveguide sensor surface affect at least one characteristic of light travelling through said waveguide sensor
- light travelling through said waveguide sensor is for eventual reception by an optical detector.
- a Mach-Zehnder interferometer having a first and a second arm, said first arm being a sensor arm having an optical sensor element, said optical sensor element comprising:
A further aspect of the invention provides a sensor for use in detecting molecules in a liquid or gas medium, the sensor comprising:
-
- a substrate layer,
- a light waveguide sensor element adjacent said medium
- a lower cladding layer between said sensor element and said substrate layer
- wherein
- molecular interactions at the waveguide surface affect at least one characteristic of light travelling through said waveguide sensor element
- and wherein said sensor element is configured as a ring resonator.
In another aspect, the present invention provides a sensor for use in detecting molecules in a liquid or gas medium, the sensor comprising:
-
- a substrate layer,
- a light waveguide sensor element adjacent said medium
- a lower cladding layer between said sensor element and said substrate layer
- wherein
- molecular interactions at the waveguide surface affect at least one characteristic of light travelling through said waveguide sensor element
- and wherein said sensor element is configured as one arm of a Mach-Zehnder interferometer.
The invention will be described with reference to the accompanying drawings, wherein:
Referring to
Referring to
The sensor detects molecular interactions (or the presence of specific molecules) by having light passed through the sensor. The sensor detects the binding of specific, target molecules to receptor molecules on the waveguide surface. By detecting this binding, the presence of the target molecules is determined. The receptor molecules are previously attached (perhaps as a layer) to the waveguide surface. As an example, an antibody can be fixed to the sensor surface (the waveguide surface) to functionalize the antibody for detecting the presence of the corresponding antigen.
Referring to
As is well-known in the art, especially to those well-versed in SPR technology, target molecules are detected when they bind to the surface 50A of the sensor. Light travelling in the waveguide 20 (in the direction 60 of propagation) produces an evanescent optical field 70 on the surface of the waveguide 20. The molecular interactions occurring near or at the surface 50A affect the refractive index of the liquid solution, thereby slowing down or delaying the light travelling through the waveguide. This effectively changes the speed and other characteristics of the light in the waveguide. Characteristics such as the intensity and the phase of the light are affected by the extent and number of molecular interactions on the surface of the waveguide.
Molecular interactions, such as the adsorption of molecules onto the sensor surface affect the speed of light as well as the attenuation of the light. The attenuation of the light also depends on the absorption cross section at the optical wavelength of the light travelling in the waveguide. As noted above, a phase change in the light in the waveguide may also be induced due to the adsorption of a molecular layer on the surface of the waveguide.
The changes in the characteristic of the light in the waveguide can be detected and measured by the use of well-known devices and techniques. Such devices as Mach-Zehnder interferometers and resonators may be used to measure these changes in characteristic. These same devices may be used to determine the initial characteristics of the light prior to their entering the sensor. Once the initial characteristics of the light are determined, these can be compared to the characteristics of the light after the light has passed through the sensor. The differences between these two sets of characteristics (such as speed of light, phase, etc.) would indicate the presence and number of molecular interactions detected.
Referring to
Experiments have shown that best results have been observed when silicon-on-insulator waveguides were used. Silicon photonic wire waveguides have been found to produce useful as the sensor elements in the sensor. For better results, a sensor window may be used to isolate the area where the waveguide core is exposed to the target molecules, to enable a comparison of the light travelling through the sensor waveguide with light travelling in an unexposed reference waveguide. Referring to
It should be noted that various configurations of the above noted sensor are possible. Referring to
Experiments have also shown that better results have been achieved when the waveguides were thin as well as having a high contrast in terms of refractive index. Thus, better results were found when the contrast between the effective refractive index (Neff) and the refractive index of the cladding was at a maximum. Also, it has been found that better results were achieved when the polarization of the light travelling in the waveguide was perpendicular to the active surface (the so-called TM mode). One material which produced acceptable results (thin waveguide, high index contrast, and TM mode) were silicon photonic wire waveguides. However, other materials may also provide equally acceptable results.
It should also be noted that the presence of a thin layer (i.e. the layer must be thinner than the extent of the evanescent field above the waveguide) of silicon dioxide between the waveguide and the medium containing the molecular interactions does not significantly degrade the performance (sensitivity) of the sensor. As such, a layer of silicon dioxide (i.e. glass) may be deposited on the waveguide.
Based on the above, silicon or other established glass bio-chip chemistries may be used in the production of the above noted sensor elements.
The above sensor technology may be used in a number of configurations. These configurations may enhance the results obtained by the sensor by increasing the area exposed to the material being sensed or the configurations may make it easier to interrogate the sensor.
The sensors may be arranged as a sensor block with multiple sensors.
Referring to
Referring to
The spiral section may also be configured as a bifilar spiral. Such arrangement obviates the need for a mirror and provides physically separated input and output waveguides.
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
The output of each arm is then joined into a single output 1040. As with the previous configurations, the section of the waveguide in the sensor window is exposed to the material being sensed. The other sections of the light waveguide are shielded from the material being sensed. In this configuration, if the two arms are designed to have precisely the same optical path length and the same average dNeff/DT (with Neff being the effective index of the waveguide mode) the output of the Mach-Zehnder will be independent of temperature and wavelength. The sensor block will only respond to the molecular adsorption and index changes in the material over the sensor window.
The configuration in
The ring resonator configuration and the Mach-Zehnder configuration may be combined into a single sensor block as in
The Mach-Zehnder configuration of the sensor block may be combined with other sensor blocks to arrive at an array of sensor blocks. Referring to
The Mach-Zehnder configuration may also be altered to arrive at other, useful sensor blocks. As an example, referring to
While conventional Mach-Zehnder interferometer configurations are contemplated in the configurations noted above, more unconventional MZ configurations are also useful. As an example, unbalanced Mach-Zehnder interferometers or ring couplers may be used. Referring to
Referring to
In the configuration of
In the configurations of
For the sensing window in a Mach-Zehnder interferometer, a photonic crystal structure, resonator, or grating may be used to increase the group index. This would thereby amplify the phase change induced by the molecular adsorption in the sensor window and increase sensitivity. (See
It should be noted that the ring resonators and Mach-Zehnder based sensors may be used in different configurations possible with this sensor technology. An array of sensors (with each sensor being a ring resonator, Mach Zehnder, or other type of sensor) is also possible and such a configuration would allow for the use of a broadband light source as the input signal. Referring to
The configuration in
If a single input signal and a single output signal is desired, a configuration as illustrated in
A person understanding this invention may now conceive of alternative structures and embodiments or variations of the above all of which are intended to fall within the scope of the invention as defined in the claims that follow.
Claims
1. An optical sensor block for use in detecting molecules in a liquid or gas medium, the sensor block comprising:
- a group of sensors comprising at least two sensor elements wherein each sensor element comprises a substrate layer a light waveguide sensor adjacent said medium a lower cladding layer between said waveguide sensor and said substrate layer wherein molecular interactions at the waveguide sensor surface affect at least one characteristic of light travelling through said waveguide sensor light travelling through said waveguide sensor is for eventual reception by an optical detector.
2. An optical sensor block according to claim 1 wherein said sensor block has a single optical input and said sensor block further comprises an optical signal splitting means.
3. An optical sensor block according to claim 1 wherein said sensor block has a plurality of optical inputs.
4. An optical sensor block according to claim 3, wherein said plurality of optical inputs are coupled to said sensors through an array of vertical waveguide couplers.
5. An optical sensor block according to claim 4, wherein at least one of said array of vertical waveguide couplers is a diffraction grating.
6. An optical sensor block according to claim 4 wherein at least one of said array of vertical waveguide couplers is a 45 degree mirror.
7. An optical sensor block according to claim 2 wherein said optical splitting means is an optical splitter for splitting said single optical input between said at least two sensor elements in said group.
8. An optical sensor block according to claim 2 wherein said optical splitting device is an optical demultiplexer for demultiplexing said single optical input between said at least two sensor elements in said group.
9. An optical sensor block according to claim 1 wherein at least one sensor element in said sensor block is configured as an optical ring resonator such that for said at least one sensor element, said light waveguide sensor is configured as a ring.
10. An optical sensor block according to claim 1 wherein at least one sensor element in said sensor block is configured as a two-mirror resonator, such that for said at least one sensor element, said light waveguide sensor is in a waveguide resonator cavity formed between two mirrors.
11. A sensor block according to claim 1 wherein at least one sensor element in said sensor block is configured as a spiral such that for said at least one sensor element, said light waveguide sensor adjacent said medium is arranged as a spiral.
12. A sensor block according to claim 1 wherein at least one sensor element in said sensor block has said light waveguide sensor arranged and configured as a single weft weaving pattern with each trace of said pattern being parallel to other traces to result in a grid-like pattern of parallel lines adjacent said medium
13. A sensor block according to claim 1 wherein at least one sensor element in said sensor block comprises waveguide sections with different dn/dT characteristics for reducing sensor temperature sensitivity.
14. A sensor block according to claim 9 wherein the or each of said at least one sensor element is configured as a ring resonator and has a specific resonance wavelength such that an input beam having said specific wavelength passes through said ring resonator.
15. An optical sensor block for use in detecting molecules in a liquid or gas medium, the sensor block comprising:
- a Mach-Zehnder interferometer having a first and a second arm, said first arm being a sensor arm having an optical sensor element, said optical sensor element comprising: a substrate layer a light waveguide sensor adjacent said medium a lower cladding layer between said waveguide sensor and said substrate layer wherein
- molecular interactions at the waveguide sensor surface affect at least one characteristic of light travelling through said waveguide sensor
- light travelling through said waveguide sensor is for eventual reception by an optical detector.
16. An optical sensor block according to claim 15 wherein said optical sensor element is configured as a ring resonator with said light waveguide sensor being configured as a ring.
17. An optical sensor block according to claim 15 wherein said second arm is a reference arm having a modulator.
18-21. (canceled)
22. A sensor for use in detecting molecules in a liquid or gas medium, the sensor comprising:
- a substrate layer,
- a light waveguide sensor element adjacent said medium
- a lower cladding layer between said sensor element and said substrate layer
- wherein
- molecular interactions at the waveguide surface affect at least one characteristic of light travelling through said waveguide sensor element
- and wherein said sensor element is configured as one arm of a Mach-Zehnder interferometer.
23. A sensor according to claim 22 wherein said sensor element comprises a thin, high refractive index contrast waveguide.
24. A sensor according to claim 22 wherein said sensor element comprises a silicon photonic waveguide.
25. A sensor according to claim 22 wherein said lower cladding layer comprises a layer of silicon oxide.
Type: Application
Filed: Apr 9, 2008
Publication Date: Jul 1, 2010
Inventors: Dan-Xia Xu (Gloucester), Adam Densmore (Orleans), Andre Delage (Gloucester), Pavel Cheben (Ottawa), Siegfried Janz (Gloucester)
Application Number: 12/451,608
International Classification: G01B 9/02 (20060101); G02B 6/00 (20060101);