Gas sensor

Abstract

We describe a method of selectively detecting the presence of an analyte. The method comprises providing a waveguide with a core comprising porous material; absorbing an analyte sample into the porous material of the core such that the analyte sample is held within pores of the core; waveguiding radiation along the waveguide to an output; measuring spectral features of the output radiation due to absorption or scattering of said waveguided radiation by the absorbed analyte sample; and selectively identifying the presence of a target analyte in the sample from the spectral features. In embodiments spectral features are measured for multiple different waveguide core regions having different physical/chemical properties modified to provide additional selectivity to the target analyte(s), and these measurements are combined to identify the target analyte.

1 . A method of selectively detecting the presence of an analyte, the method comprising:
 providing at least one waveguide, the waveguide having a core comprising porous material;   absorbing an analyte sample into said porous material of said core such that said analyte sample is held within pores of said core;   waveguiding radiation along said at least one waveguide to an output to provide output radiation;   measuring one or more spectral features of said absorbed analyte sample in said output radiation due to absorption or scattering of said waveguided radiation by said absorbed analyte sample;   selectively identifying the presence of a target analyte in said analyte sample from said one or more spectral features;   wherein molecular absorption or Raman spectroscopy is performed on said analyte sample.   
     
     
         2 . A method as claimed in  claim 1  wherein said one or more spectral features are enhanced by capillary condensation. 
     
     
         3 . A method as claimed in  claim 1  further comprising providing a plurality of waveguide core regions with a plurality of different physical and/or chemical modifications to said core, wherein said plurality of waveguide core regions comprise one or both of a plurality of core regions of a plurality of said waveguides and a plurality of core regions of a plurality of portions of said at least one waveguide;
 waveguiding radiation through said plurality of waveguide core regions; 
 measuring one or more said spectral features for each of said differently modified core regions; and 
 selectively identifying said target analyte from a combination of said spectral features for said differently modified core regions. 
 
     
     
         4 . A method as claimed in  claim 3  wherein said differently modified core regions have pores with size distributions having peaks at different pore sizes. 
     
     
         5 . A method as claimed in  claim 3  or wherein said differently modified on regions comprise different functionalisations of said core material. 
     
     
         6 . A method as claimed in  claim 3 , wherein said selective identifying uses a multi-component analysis of said combination of spectral features. 
     
     
         7 . A method as claimed in  claim 1  further comprising operating at a plurality of temperatures of said at least one waveguide, and measuring said one or more spectral features at said plurality of temperatures; wherein said selective identifying is responsive to said one or more spectral features at said plurality of temperatures. 
     
     
         8 . A method as claimed in  claim 7  wherein said temperatures are selected to change a degree of vapour condensation of said target analyte within said pores of said core. 
     
     
         9 . A method as claimed in  claim 1  wherein said measuring comprises waveguiding multiband radiation along said waveguide and measuring a spectrum of said output radiation. 
     
     
         10 . A method as claimed in  claim 1  wherein said pores have a size distribution with a peak at less than 500 nm. 
     
     
         11 . A method as claimed in  claim 1  comprising providing said waveguide on substrate and using porous silicon or porous silica for said core. 
     
     
         12 . An analyte sensor, the sensor comprising:
 a substrate bearing a waveguide, the waveguide comprising:   a first, cladding layer on said substrate;   a second, core layer, comprising porous material, over said cladding layer;   a radiation source to provide radiation into said waveguide;   a radiation detector to detect radiation which has been waveguided along said waveguide; and   a signal processor, coupled to said radiation detector, to identify the presence of a target analyte absorbed within said core layer from one or more spectral features of said detected radiation due to absorption or scattering of said waveguided radiation by said absorbed target analyte.   
     
     
         13 . An analyte sensor as claimed in  claim 12  wherein said core layer and said cladding layer each comprise a porous silicon-based material. 
     
     
         14 . A method of fabricating an analyte sensor waveguide as claimed in  claim 13 , the method comprising:
 providing a silicon substrate;   supplying a first current at a first current density perpendicular to said substrate;   performing a first etch of said substrate to fabricate said core layer; and   supplying a second current at a second density slowly perpendicular to said substrate;   performing a second etch of said substrate to fabricate said core layer.   
     
     
         15 . A method of fabricating an analyte sensor, comprising fabricating a waveguide as claimed in claimed  14 , and then fabricating said analyte sensor using said waveguide. 
     
     
         16 . Apparatus for selectively detecting the presence of an analyte, the apparatus comprising:
 at least one waveguide, the waveguide having a core comprising porous material;   a radiation source to provide radiation into said waveguide;   a radiation detector to detect radiation which has been waveguided along said waveguide; and   a signal processor, coupled to said radiation detector, to identify the presence of a target analyte absorbed within said core layer from one or more spectral features of said target analyte in said detected radiation due to absorption or scattering of said waveguided radiation by said absorbed target analyte.   
     
     
         17 . Apparatus as claimed in  claim 16  comprising a plurality of waveguide core regions with a plurality of different physical and/or chemical modifications to said core; wherein said plurality of waveguide core regions comprise one or both of a plurality of core regions of a plurality of said waveguides and a plurality of core regions of a plurality of portions of said at least one waveguide. 
     
     
         18 . A method as claimed in  claim 17  wherein said signal processor is configured to selectively identify said target analyte from a combination of said spectral features for said differently modified core regions. 
     
     
         19 . A method as claimed in  claim 16 , further comprising a temperature controller to control a temperature of said at least one waveguide to a plurality of different temperatures; and wherein said signal processor is configured to selectively identify said target analyte by measuring said one or more spectral features at said plurality of different temperatures. 
     
     
         20 . A method of analysing a bodily fluid sample using the method of  claim 1 . 
     
     
         21 . Apparatus as claimed in  claim 16  for analysing a bodily fluid sample, the apparatus further comprising a bodily fluid sample holder, and means to selectively allow passage of bodily fluid vapour from the sample holder for analysis.