Abstract: Active agents such as proteins are covalently immobilized on substrates carrying hydroxyl groups. A silane is bound to the substrate and coupled to a heterobifunctional crosslinker at one functional group leaving a free functional group, different than the first group, to which a protein is bound while retaining high protein functionality. Preferably, the silane has a functional group which reacts with the hydroxyl group of the substrate and a thiol terminal group which reacts with a functional group of a heterobifunctional crosslinking agent which contains a succinimide group that reacts with an amino group of the active agent. Bound active agents such as proteins are useful as biosensors or reactants in a variety of applications including bioassays.