ASSESSMENT OF CATALYST-MODIFIED CONDUCTING POLYMERS FOR THE DEVELOPMENT OF AMPEROMETRIC DEHYDROGENASE ELECTRODES

Abstract

Redoxreactions at mediator-modified electrode surfaces have to be optimized for the development of amperometric enzyme electrodes. This is of special importance for dehydrogenaseelectrodes, where the electrochemical reoxidation of the reduced cofactor NADH via a covalently bound mediatorhas to occur avoiding intermediate radicals. Recently, we have described the synthesis and the electrocatalytic properties of copolymers of pyrrole and 1-(1-pyrrolo)-2,4,5-trichloro benzoquinonefor the mediated oxidation of NADH (1). In this case, the electrocatalytic activity of the catalyst-modified electrode surface, its long-term stability, the porosity and morphology of the conducting polymerfilm and the adhesion on the electrode surface have to be evaluated and enhanced. Until now, the electrocatalytic activity of modified electrode surfaces has been investigated by meansofcyclic voltammetry or constantpotential chronoamperometry. However, the enzyme, necessary coenzymes, and/or mediators have to be present dissolved in the electrolyte, and hence sucha solution could only be used once. Especially with very expensive enzymes orthose which aredifficult to isolate, this does not seem to be a possible way for the optimization of electrode characteristics. Additionally, the simple physical immobilization of dissolved enzymesin front of the electrode surface by meansof a dialysis membrane doesnotlead to a reproducible amount andactivity of the enzymewithin the electrode chamber. Onthe other hand, the application of enzyme reactors with enzymescovalently bound on controlled porousglass is well knownin flow-injection systems. These enzyme-modified glass can be obtainedeasily, the activity of the thus immobilized enzymesis in generalstabilized, and the enzyme activity/mg glass can be determined by conventional Spectrophotometric activity assays. In this communication, the application of dehydrogenases covalently bound to controlled-porous glass and physically retained by meansof a dialysis membranein front of a chloranil-modified conducting polymerelectrodeis investigated. By this method, a reproducible amountof enzymecan be kept near the catalytically active electrode, and thus amperometric dehydrogenaseelectrodes can be compared with respect to the electrocatalytic properties of the redox polymerfilm.