Optical analyte sensor

A method for detecting an analyte, comprising the steps of:

• providing an analyte sensor, comprising in combination:
• a light source for generating light having a chosen wavelength or band of wavelengths;
• an optical guide having a first surface and an axis, capable of receiving light from said light source and for guiding the light along the axis, and having at least one region on the first surface thereof wherein an evanescent field is generated substantially perpendicular to the axis of said guide such that the evanescent field extends from the first surface within the at least one region;
• at least one detector disposed in the vicinity of the at least one region of said guide and ≦45 μm from said guide, for detecting the intensity of the evanescent field;
• and
• a substrate not interposed between said optical guide and said at least one detector, for supporting said waveguide and said detector, whereby the analyte in the vicinity of the at least one region modifies the distribution of the evanescent field thereby changing the intensity thereof detected by said at least one detector;
• introducing light having a chosen wavelength or band of wavelengths into said optical guide;
• contacting the analyte with the evanescent field exiting the at least one region, whereby the analyte modifies the distribution of the evanescent field thereby changing the intensity thereof;
• and
• detecting the change of intensity of the evanescent field extending from the at least one region of the first surface in the vicinity of the at least one region to detect the presence of analyte.