Diffraction anomaly sensor having grating coated with protective dielectric layer

Abstract

A method and apparatus for optically assaying a targeted substance in a sample using a diffraction anomaly grating sensor. The optical sensor has a diffraction grating coated with at least one dielectric layer such that the sensor is sensitized to interact with the targeted substance. Upon interaction, light incident upon the sensor at a particular angle propagates through the dielectric, thereby exhibiting a dip in zero-order reflectance. Advantages of the present invention include facilitating increased sensitivity while protecting the metal grating from tarnishing and degradation. The present invention also allows for the construction of sensors that are sensitized to a plurality of substances, thus eliminating the need for an operator to reconfigure the sensing system in order to assay different substances.

I claim:  
     
       1. A sensor for assaying a substance in a sample comprising: 
       a substrate having a plurality of parallel grooves in a surface;  
       a metal layer formed outwardly from the surface of the substrate, the metal layer substantially conforming to the grooved surface of the substrate; and  
       a dielectric layer formed outwardly from the metal layer, the dielectric layer for suppressing reflection of incident light having a polarization parallel to the grooves of the substrate  
       wherein for light having a plane of incidence perpendicular to the grooves of the substrate the dielectric layer suppresses a component of the light having a polarization parallel to the grooves of the substrate.  
     
     
       2. The sensor of claim  1 , further comprising a sensitizing layer formed outwardly from the dielectric layer, wherein the sensitizing layer interacts with the substance in the sample. 
     
     
       3. The sensor of claim  1 , wherein the dielectric layer interacts with the substance in the sample. 
     
     
       4. The sensor of claim  1 , wherein the dielectric layer has a thickness of at least 50 nm. 
     
     
       5. The sensor of claim  1 , wherein the dielectric layer has a thickness of at least 130 nm. 
     
     
       6. The sensor of claim  1 , wherein a cross-sectional shape of the grooved surface of the substrate is substantially periodic. 
     
     
       7. The sensor of claim  6 , wherein the cross-sectional shape of the grooved surface is selected from the set of sinusoidal, trapezoidal and triangular. 
     
     
       8. The sensor of claim  2 , wherein the sensitizing layer comprises a layer of antigens. 
     
     
       9. A sensor for assaying a plurality of substances in a sample comprising: 
       a substrate having a plurality of parallel grooves in a surface;  
       a metal layer formed outwardly from the surface of the substrate, the metal layer substantially conforming to the grooved surface of the substrate; and  
       a plurality of substantially non-overlapping dielectric layers formed along the metal layer for suppressing reflectance of an incident light beam having a polarization component parallel to the grooves of the substrate and a plane of incidence perpendicular to the grooves of the substrate.  
     
     
       10. The sensor of claim  9 , wherein each dielectric layer interacts with at least one of the plurality of substances in the sample. 
     
     
       11. The sensor of claim  9 , further comprising a sensitizing layer formed outwardly from the plurality of dielectric layers, the sensitizing layer capable of interacting with the substance in the sample. 
     
     
       12. The sensor of claim  9 , wherein each of the dielectric layers has a thickness of at least 50 nm. 
     
     
       13. The sensor of claim  9 , wherein each of the dielectric layers has a thickness of at least 130 nm. 
     
     
       14. The sensor of claim  9 , wherein a cross-sectional shape of the grooved surface of the substrate is substantially periodic. 
     
     
       15. The sensor of claim  14 , wherein the cross-sectional shape of the grooved surface is selected from the set of sinusoidal, trapezoidal and triangular. 
     
     
       16. The sensor of claim  11 , wherein the sensitizing layer comprises a layer of antigens. 
     
     
       17. A method for assaying a substance in a sample comprising the steps of: 
       providing a sensor having a metal diffraction grating coated with a dielectric layer;  
       emitting a light beam having a polarization component parallel to grooves in the metal diffraction grating and incident within a plane perpendicular to the grooves in the metal diffraction grating;  
       exposing the sensor with the light beam over a plurality of incident angles;  
       detecting a first diffraction anomaly angle during the first exposing step at which zero-order reflectance of the incident light changes;  
       interacting the sensor with the sample;  
       exposing the sensor a second time with a light beam over the plurality of incident angles;  
       detecting a second diffraction anomaly angle during the second exposing step; and  
       determining a measure of the substance in the sample as a function of the first angle and the second angle.  
     
     
       18. The method of claim  17 , further comprising the step of sounding an alarm when the determined measure of the substance in the sample exceeds a predetermined threshold. 
     
     
       19. A method for assaying a substance in a sample comprising the steps of: 
       providing a sensor having a metal diffraction grating having a plurality of grooves, wherein the metal diffraction is coated with a dielectric layer;  
       exposing the sensor with a light beam having a polarization component parallel to the grooves of the grating and incident within a plane perpendicular to the grooves in the grating, and further wherein the component propagates substantially within the dielectric layer when the sensor is exposed with the light beam at a diffraction anomaly angle;  
       interacting the sensor with the sample; and  
       determining a measure of the substance in the sample as a function of a shift in the diffraction anomaly angle.  
     
     
       20. The method of claim  19 , wherein the exposing step comprises the step of polarizing the light beam parallel to the grooves in the metal diffraction grating. 
     
     
       21. The method of claim  19 , further comprising the step of sounding an alarm when the determined measure of the substance in the sample exceeds a predetermined threshold. 
     
     
       22. The method of claim  19 , wherein the determining step comprises the steps of: 
       splitting a reflected light beam from the sensor into a first light beam having a polarization vector parallel to grooves in the metal diffraction grating and a second light beam having a polarization vector perpendicular to grooves of the metal diffraction grating, wherein the first light beam and the second light beam each have a corresponding intensity; and  
       monitoring a ratio of the intensities of the first light beam and the second light beam.  
     
     
       23. A method for assaying a plurality of substances in a sample comprising the steps of: 
       providing a sensor having a metal diffraction grating coated with a plurality of substantially non-overlapping dielectric layers, each dielectric layer for interacting with at least one of the substances in the sample, wherein the diffraction grating has a plurality of parallel grooves;  
       selectively exposing at least one of the dielectric layers with a light beam at a corresponding diffraction anomaly angle and incident within a plane perpendicular to the grooves such that a component of the light beam having a polarization parallel to the grooves in the sensor propagates substantially within the exposed dielectric layer;  
       interacting the sensor with the sample; and  
       determining a measure for each substance in the sample as a function of a shift in the diffraction anomaly angle of the corresponding dielectric layer capable of interacting with the substance.  
     
     
       24. The method of claim  23 , further comprising the step of sounding an alarm when the determined measure of each substance in the sample exceeds a corresponding one of a plurality of predetermined thresholds. 
     
     
       25. A system for assaying a substance in a sample, comprising: 
       a sensor sensitized for interacting with the substance in the sample comprising:  
       a substrate having a grooved  plurality of parallel grooves in a surface,  
       a metal layer formed outwardly from the surface of the substrate, the metal layer substantially conforming to the grooved surface of the substrate, and  
       a dielectric layer formed outwardly from the metal layer;  
       a light source exposing the sensor with a light beam at an angle of incidence  having a plane of incidence perpendicular to the grooves in the surface of the substrate;  
       a detector receiving light reflected from the sensor, the detector responsive to light polarized parallel to the grooves in the surface of the substrate; and  
       a controller coupled to the detector for calculating a measure of the substance in the sample as a function of an anomaly angle at which a change in zero-order reflectance of the light beam occurs.  
     
     
       26. The system of claim  25 , wherein the sensor further comprises a sensitizing layer formed outwardly from the dielectric layer. 
     
     
       27. The system of claim  25 , wherein the dielectric layer interacts with the substance in the sample. 
     
     
       28. The system of claim  25 , wherein the dielectric layer has a thickness of at least 50 nm. 
     
     
       29. The system of claim  25 , wherein the dielectric layer has a thickness of at least 130 nm. 
     
     
       30. The system of claim  25 , wherein a cross-sectional shape of the grooved surface of the substrate is substantially periodic. 
     
     
       31. The system of claim  30 , wherein the cross-sectional shape of the grooved surface is selected from the set of sinusoidal, trapezoidal and triangular. 
     
     
       32. The system of claim  26 , wherein the sensitizing layer comprises a layer of antigens. 
     
     
       33. The system of claim  25  wherein the detector further comprises: 
       a polarizing beamsplitter for receiving the reflected light and splitting the reflected light into a first component and a second component, wherein the first component has a polarization vector parallel to the grooves of the substrate and the second component has a polarization vector perpendicular to the grooves of the substrate;  
       a first detector for receiving the first component of the reflected light, wherein the first detector has an output signal representative of an intensity of the first component; and  
       a second detector for receiving the second component of the reflected light, wherein the second detector has an output signal representative of an intensity of the second component, wherein the controller ratios the output signal of the first detector and the output signal of the second detector, and further wherein the controller determines the anomaly angle according the ratio of the output signals.  
     
     
       34. The system of claim  25  wherein the light beam has a polarization parallel to the grooves in the surface of the sensor.