Polymer-coated optical structures.
A method of treating the surface of an optical structure which comprises forming on said surface a thin layer of organic polymer using a solvent casting technique. Preferably the process includes the subsequent treatment of the polymer layer with a solution of a specific ligand. Complex formation between the bound ligand and its specific binding partner present in a sample to be analysed alters the optical properties of the diffraction grating surface and the change can form the basis of an assay method.