A method of immobilising a biological molecule on a substrate comprises: (i) covalently attaching a substantially three-dimensional polysilane polymer to a substrate; and (ii) attaching a biological molecule onto and/or within the polymer. The method may additionally comprise the steps of coating the substrate (or the chemically protective layer) with a layer of radiation sensitive material, exposing the substrate to a source of radiation, and incubating the substrate in the presence of a first species of biological molecule.