Differential detection for surface plasmon resonance sensor and method

Abstract

A differential measurement design employing two nearly collinear optical beams provides surface plasmon polariton resonance (SPR) sensors and a corresponding method of increased dynamic range and signal to noise ratio. The differential measurement device and method based on wavelength interrogation, employs a single incident polarization state, and is combined with a 2-D nanohole array for operation at near-normal incidence, where this approach offers a decrease in the measurement time.

What is claimed is: 
     
         1 . In a surface plasmon resonance sensor having a metal-dielectric interface formed by microfluidic channels integrated with metal-dielectric layer chips, the method comprising:
 imaging a pair of collimated laser beams at different angles of incidence onto substantially the same spot on a metal nanohole array sample at the metal-dielectric interface to excite surface plasmons on the array sample and forming a pair of transmitted laser beams emerging from the array sample;   forming a pair of parallel laser beams corresponding to the pair of transmitted laser beams;   obtaining a pair of device transfer function (DTF) signals from the pair of parallel laser beams, where each respective DTF signal has a different angle of incidence and an intensity peak at a different wavelength relative to a reference wavelength;   calculating a difference signal from the pair of DTF signals, where the difference signal has positive and negative values about a zero crossing axis which are representative of transmittivity relative to wavelength and where a resulting shift in the location of the difference signal at the zero crossing axis represents a changing refractive index of the dielectric at the metal-dielectric interface.   
     
     
         2 . The method of  claim 1  where the resonance sensor is in a closed loop configuration. 
     
     
         3 . The method of  claim 2  including obtaining the DTF signals at FWHM (Full Width Half Maximum) values. 
     
     
         4 . The method of  claim 3  where the array sample is a grating array. 
     
     
         5 . A surface plasmon resonance sensor having a metal-dielectric interface formed by microfluidic channels integrated with metal-dielectric layer chips, the sensor comprising:
 laser means for generating and imaging a pair of collimated laser beams at different angles of incidence onto substantially the same spot on a metal nanohole array sample at the metal-dielectric interface to excite surface plasmons on the array sample and forming a pair of transmitted parallel laser beams emerging from the array sample;   processor means for obtaining a pair of device transfer function (DTF) signals from the pair of parallel laser beams, where each respective DTF signal has a different angle of incidence and an intensity peak at a different wavelength relative to a reference wavelength and for calculating a difference signal from the pair of DTF signals, where the difference signal has positive and negative values about a zero crossing axis which are representative of transmittivity relative to wavelength and where a resulting shift in the location of the difference signal at the zero crossing axis represents a changing refractive index of the dielectric at the metal-dielectric interface.   
     
     
         6 . The sensor of  claim 5  wherein the sensor operates in a closed loop configuration. 
     
     
         7 . The sensor of  claim 5  wherein the processor means obtains the DTF signals at FWHM (Full Width Half Maximum) values. 
     
     
         8 . The sensor of  claim 5  where the array sample is a grating array. 
     
     
         9 . The sensor as in  claim 8  where the laser means includes a laser for generating a range of tunable laser beams and beam splitter means for generating the pair of collimated laser beams. 
     
     
         10 . The sensor as in  claim 9  including detector means for obtaining the DTF signals. 
     
     
         11 . The sensor as in  claim 10  including a computer for calculating the difference signal. 
     
     
         12 . A surface plasmon resonance sensor operating in a closed loop configuration and having a metal-dielectric interface formed by microfluidic channels integrated with metal-dielectric layer chips, the sensor comprising:
 laser means for generating and imaging a pair of collimated laser beams at different angles of incidence onto substantially the same spot on a metal nanohole grating array sample at the metal-dielectric interface to excite surface plasmons on the array sample and forming a pair of parallel laser beams emerging from the array sample;   processor means for obtaining a pair of device transfer function (DTF) signals at FWHM (Full Width Half Maximum) values from the pair of parallel laser beams, where each respective DTF signal has a different angle of incidence and an intensity peak at a different wavelength relative to a reference wavelength and for calculating a difference signal from the pair of DTF signals, where the difference signal has positive and negative values about a zero crossing axis which are representative of transmittivity relative to wavelength and where a resulting shift in the location of the difference signal at the zero crossing axis represents a changing refractive index of the dielectric at the metal-dielectric interface.   
     
     
         13 . The sensor of  claim 12  where the processor means includes a pair of detectors and where the pair of parallel laser beams impinge on the pair of detectors. 
     
     
         14 . The sensor of  claim 12  where the pair of collimated laser beams are transmitted through the grating array sample. 
     
     
         15 . The sensor of  claim 12  where the pair of collimated laser beams are reflected from the grating array sample. 
     
     
         16 . The sensor of  claim 12  including means for detecting the differential intensity of the pair of parallel laser beams.