Biological sensors

Claim 1

A sensor for use in biological, biochemical or chemical testing, said sensor comprising: an optical waveguide having an input end and an output end and along which radiation may propagate by means of internal reflections off its internal surfaces, a source of electromagnetic radiation whose output is applied to the input end of said optical waveguide, and wherein said output end of the optical waveguide is cut off at an angle to its axis to provide a sloping end face, wherein said radiation is input to the waveguide as a focussed beam so that the beam is incident at said end face as a spread of angles, and wherein the angle of the sloping end face is such as to (1) cause the incident beam to be totally internally reflected at said face, and (2) cause the thus-reflected beam to be incident on the wall of the waveguide at an angle sufficiently great for it to exit from the waveguide without being subject to further internal reflection, means for monitoring the radiation from said source which is internally reflected at said face, a layer of metallic material applied to said sloping face, a layer of sensitive material applied to the metallic layer, and means for introducing onto the sensitive layer so as to react therewith a sample to be analyzed, the arrangement being such that the aforesaid spread of radiation incident at said face of the optical waveguide is such as to include that angle at which surface plasmon resonance occurs, and allows the changing characteristics of the resonance to be monitored, which characteristics, as detected by said monitoring means, are dependent upon the reaction between the sample and the sensitive layer.