The invention relates to an activated metallic, semiconductor, polymer, composite and/or ceramic substrate, the substrate being bound through a mixed or graded interface to a hydrophilic polymer surface that is activated to enable direct covalent binding to a functional biological molecule, the polymer surface comprising a sub-surface that includes a plurality of cross-linked regions, as well as to such activated substrates that have been functionalised with a biological molecule and to devices comprising such functionalised substrates. Such substrates can be produced by a method comprising steps of: a. exposing a surface of the substrate to any or more of (i) to (iii): (i) plasma ion implantation with carbon containing species (ii) co-deposition under conditions in which substrate material is deposited with carbon containing species while gradually reducing substrate material proportion and increasing carbon containing species proportion (iii) deposition of a plasma polymer surface layer with energetic ion bombardment incubating the surface treated according to step (a) with a desired biological molecule.
