Patent ID: 6885455

Claim:
In a surface plasmon resonance sensor or critical angle sensor having a housing containing a light source and a photodetector, the housing having a sensing surface having altered optical properties when in contact with a sample and a reflecting surface for directing light within the housing so that light from the light source is reflected by the sensing surface and the reflecting surface onto the photodetector, a self contained calibration standard wherein the reflector surface comprises an optically flat surface on the housing having no reflective material thereon and having an outside of the flat surface exposed to air and wherein the housing is made of a light transmissive material for light from the light source having a higher index of refraction than air, light impinging on the flat surface having an angle of incidence which is equal to or greater than a critical angle being reflected to a path which impinges onto the photodetector, whereby a characteristic response is detected by the photodetector which is indicative of a calibration point.