METHOD AND APPARATUS FOR ASSAYING A SPECIES IN A SAMPLE

A method and apparatus for assaying a species in a biological sample fluid. The apparatus comprises an SAW device (1) comprising a slab (2) of piezoelectric material on the upper surface (5) of which is formed an input transducer (3) and an output transducer (4). A source of RF energy is applied to the input transducer to generate a surface acoustic wave. Applied to the surface (5) is a thin layer (8) of a material capable of binding a species to be assayed. The sample (13) to be tested is applied to the top of the layer (8). A collimated light beam (1) from a source (9) is applied to the thin film from underneath the slab (2) and is collected by a photodetector (12). When the slab (2) is energised, the vibration sets up an effective diffraction grating which is coupled to the thin film and acts to diffract the light beam (10) applied to it. The energy in the diffracted beam, as measured by the photodetector (12), is indicative of the progress and result of the reaction between the layer 8 and the sample.