BIOLOGICAL SENSORS

A surface plasmon resonance (SPR) detector in which radiation from a laser source is reflected off a concave reflector to a point or line of incidence on the interface between a glass slide and a metal layer. The single pencil beam from the laser is scanned by a moving mirror across a small arc, covering those angles of incidence within which surface plasmon resonance occurs. A sensitive, for example antibody, layer overlies the metal layer to form a combined layer, and a sample to be tested passed across the antibody layer. Any binding which occurs with the antibody layer results in the refractive index of the layer changing, and this change may be detected by monitoring the strength of the beam internally reflected. A light detector enables the beam to be measured.