improved biosensors are provided having excellent selectivity and stability properties , together with methods of preparing the biosensors . a preferred biosensor includes an electrode having enzyme deposited thereon together with a layer of electropolymerized polymer intermingled with the enzyme ; a crosslinked silane film is applied over the polymer layer , and a final coating of polyurethane is formed over the film . in preparative procedures , the enzyme is electrodeposited using an aqueous enzyme solution containing a nonionic surfactant at a concentration level preferably in excess of the critical micelle concentration of the surfactant . in the case of a glucose sensor , the polymer layer is preferably polyphenol , while the silane film is crosslinked trimethoxysilane . the preferred biosensors have greatly enhanced selectivity stabilities .