Double resonance interrogation of grating-coupled waveguides

Abstract

A method for using a double resonance effect within a grating-coupled waveguide (GCW) sensor, as generated from a light beam with a given span of wavelengths or angles, is provided. The method can be used for label-independent detection of biological and chemical agents, to interrogate biological-binding events or chemical reactions within a sensing region at increased sensitivity, and with decreased sensitivity to environmental perturbations. Also described is an optical interrogation system incorporating the method.

1 . A label-independent detection system for detecting biological or chemical agents, the detection system comprises: 1) a substrate surface having a sensing region with a bio- or chemo-responsive layer; 2) an optical interrogation apparatus for monitoring said bio- or chemo-responsive layer, said optical interrogation apparatus comprising a grating-coupled waveguide structure, a light source, an optical delivery system, and a detection instrument, wherein more than one direction of propagation is used in said waveguide to generate a sensor response for either a given angle or wavelength.  
     
     
         2 . The detection system according to  claim 1 , wherein for a given angle or wavelength, two resonances exists as a result of light propagation in two different, symmetrical directions in the waveguide.  
     
     
         3 . The detection system according to  claim 1 , wherein said sensor response is generated simultaneously using more than one direction of propagation.  
     
     
         4 . The detection system according to  claim 1 , wherein said sensor response is generated in sequence using more than one direction of propagation.  
     
     
         5 . The detection system according to  claim 1 , wherein an angular shift as measured using both propagation directions as a function of refractive index change greater than a sensitivity obtainable from using only one direction of propagation.  
     
     
         6 . The detection system according to  claim 5 , wherein an angular shift as measured using both propagation directions as a function of refractive index change improves interrogation signal-to-noise sensitivity of said apparatus by a factor of at least about {square root}2.  
     
     
         7 . The detection system according to  claim 1 , wherein a spectral shift as measured using both propagation directions as a function of refractive index change improves an observed signal to noise ratio in said system by a factor greater than that achievable from using only one propagation direction.  
     
     
         8 . The detection system according to  claim 7 , wherein a spectral shift as measured using both propagation directions as a function of refractive index change improves an observed signal to noise ratio in said system by a factor of at least about {square root}2.  
     
     
         9 . The detection system according to  claim 1 , wherein signal from different propagation directions are used to mitigate system sensitivity to environmental perturbations.  
     
     
         10 . The detection system according to  claim 9 , wherein a difference in resonant peak locations is insensitive to an angular position of said sensor.  
     
     
         11 . The detection system according to  claim 9 , wherein the average of resonant peak locations is insensitive to an angular position of said sensor.  
     
     
         12 . The detection system according to  claim 1 , wherein signal from different propagation directions, together with mathematical corrections for waveguide dispersion, are used to mitigate system sensitivity to environmental perturbations.  
     
     
         13 . The detection system according to  claim 12 , wherein an average of resonant peak locations, modified by an appropriate waveguide dispersion correction, is insensitive to an angular position of said sensor.  
     
     
         14 . The detection system according to  claim 1 , wherein said system further includes an air-fluid delivery system, comprising either macro or micro-fluidic passages designed to deliver biological or chemical analytes to said sensing region.  
     
     
         15 . A method of detecting biological or chemical agents, the method comprises: providing a sensor system having a evanescent-field sensing region comprising a substrate surface having at least a bio- or chemo-responsive layer; generating a double resonance within a grating-coupled waveguide of said system for either a given angle or wavelength; exposing an individual sensing region to an environment with analytes; and monitoring a response from said sensor system.  
     
     
         16 . The method according to  claim 15 , wherein an angular shift as measured using both propagation directions as a function of refractive index change doubles (2×) interrogation sensitivity of said apparatus.  
     
     
         17 . The method according to  claim 15 , wherein a spectral shift as measured using both propagation directions as a function of refractive index change improves an observed signal to noise ratio in said system by a factor of at least about {square root}2.  
     
     
         18 . The method according to  claim 15 , wherein said method uses either a mean or difference of the resonance modes in a detection system.  
     
     
         19 . The method according to  claim 15 , wherein said substrate is modified with one or more materials, which enhance stable immobilization of said bio- or chemo-responsive layer.  
     
     
         20 . A biosensor comprising: 1) a substrate surface having a sensing region with a bio- or chemo-responsive layer; 2) an optical interrogation apparatus for monitoring said bio- or chemo-responsive layer, said optical interrogation apparatus comprising a grating-coupled waveguide structure, a light source, and an optical delivery system, wherein more than one direction of light propagation is used in said waveguide to generate a sensor response for either a given angle or wavelength, and a signal from different propagation directions are used to mitigate sensitivity to environmental perturbations.  
     
     
         21 . The biosensor according to  claim 20 , wherein a spectral shift as measured using both propagation directions as a function of refractive index change improves an observed signal to noise ratio in said system by a factor greater than that achievable from using only one propagation direction.  
     
     
         22 . The biosensor according to  claim 20 , wherein an angular shift as measured using both propagation directions as a function of refractive index change greater than a sensitivity obtainable from using only one direction of propagation.  
     
     
         23 . The biosensor according to  claim 22 , wherein an angular shift as measured using both propagation directions as a function of refractive index change improves interrogation signal-to-noise sensitivity of said apparatus by a factor of at least about {square root}2.  
     
     
         24 . The biosensor according to  claim 22 , wherein an angular shift as measured using both propagation directions as a function of refractive index change doubles (2×) interrogation sensitivity of said biosensor.