Disclosed herein is a method of: treating an organic polymer with an electron beam-generated plasma; exposing the treated polymer to air or an oxygen- and hydrogen-containing gas, generating hydroxyl groups on the surface of the polymer; reacting the surface with an organosilane compound having a chloro, fluoro, or alkoxy group and a functional or reactive group that is less reactive with the surface than the chloro, fluoro, or alkoxy group; and covalently immobilizing a biomolecule to the functional or reactive group or a reaction product thereof.