Covalent coupling of antigen or antibody or other protein is achieved by first reacting the glass with a silane-based coupling compound in known manner (e.g. with a terminal amino-alkyl trimethoxysilane, or another reagent substantially as e.g. the 3-aminopropyl compound another reagent substantially as described in U.S. Pat. No. 3,652,761, suitably about 2% v/v in acetone), then reacting the amin