POTENTIOMETRIC ION-SELECTIVE AND BIOSELECTIVE ELECTRODES BASED ON ASYMMETRIC POLYURETHANE MEMBRANES

The potentiometric ion responses of ammonium- and proton-selective electrodes prepared by incorporating appropriate neutral carriers within novel asymmetric polyurethane membranes are reported. The membranes are formed by first casting a plasticized polyurethane(PU)/terpoly(vinyl chloride/vinyl acetate/vinyl alcohol) (PVA)-based ion-selective membrane and then applying a thin second layer of a more hydrophilic polyurethane (HPU) containing polylysine. The resulting asymmetric membranes function equivalently to normal PU/PVA membranes and conventional poly(vinyl chloride) type membranes in terms of potentiometric ion selectivity and dynamic response properties. The large amount of amine functional groups from the polylysine within the outer hydrophilic layer can be further activated for direct enzyme immobilization. As examples, adenosine deaminase and urease are immobilized on ammonium- and proton-selective membranes, respectively, to yield adenosine and urea electrodes with good dynamic responses and sensitivities. Advantageous use of this new membrane system for preparation of solid-state microfabricated enzyme-based sensors is also described.