5] Multienzyme membrane electrodes

Abstract

Multienzyme membrane electrodes, in which more than two different types of enzymes are utilized, have been developed for the assay of α-amylase, lactose, maltose, sucrose, and creatinine. This chapter focuses on α-amylase sensors and creatinine sensors. It is most important in enzyme electrodes to combine a permselective immobilized enzyme membrane with a special electrode. The combination acts selectively toward substances, which interfere with the electrode reaction. The permselectivity toward products or reagents of the reaction, such as hydrogen peroxide, is the most important function of the membrane in an enzyme electrode. If a polarographic probe consisting of a silver cathode and a platinum anode are used as an electrochemical sensor for hydrogen peroxide, the membrane covering the probe needs to be permeable to hydrogen peroxide but must exclude other electrically oxidative substances such as uric acid and ascorbic acid. Additionally, the membrane needs to have mechanical strength. An asymmetrically structured cellulose acetate membrane has these properties. Moreover, the porous layer of the asymmetric membrane, with its large surface area, is well suited as a support for the immobilization of a large amount of enzyme per unit area.