BIOLOGICAL SENSORS

A surface plasmon resonance (SPR) sensor in which the phenomenon of long-range surface plasmon resonance is used to develop a highly sensitive detector for use in biological, biochemical or general chemical testing. The sensor comprises a laminar structure consisting of a high refractive index glass block (10), a membrane (11) of dielectric material, a thin metal layer (13), and a sensitive layer (14). A sample (15) to be tested is brought into contact with the sensitive layer (14). The refractive index of the dielectric layer and that of the layer (14/15) on the opposite side of the metallic layer (13) should be equal, or nearly so, and the refractive index of the glass block (10) should be higher than this so that total internal reflection takes place at the interface between the block (10) and the membrane (11). Light (1) from a laser source (8) is totally internally reflected at this interface, and the strength of the reflected beam (4) is monitored by a light detector (9). Provided conditions are correct, long-range SPR will take place which will sensitively alter the strength of beam (4) in dependence upon the progress of the reaction between the sensitive layer (14) and sample (15).