Coimmobilized Dehydrogenase-Coenzyme Systems for Biosensors

Abstract

This chapter describes coimmobilized dehydrogenase–coenzyme systems for biosensors. Dehydrogenases represent an important group of enzymes in clinical analysis of substrates such as ethanol, lactate and steroids. Coimmobilization methods are especially interesting for use in combination with mediator-modified electrodes to yield quasi-reagentless, amperometric biosensors. The mediator enables detection of NADH at a potential as low as 0 mV versus SCE, so there are less interferences of other electroactive substances. In addition, the mediated electron transfer ensures that the amperometric reoxidation of NADH yields the biologically active form of NAD+, making the sensor system reversible. The mediator enables electrochemical detection as well as recycling of the bound coenzyme in one step. Different methods of coimmobilization are presented with regard to the use in amperometric biosensors. The methods, however, can also be applied to other kinds of biosensors, such as, changes in UV absorption, or fluorescence due to the formation of NAD+, or NADH as well as heat formation due to the enzyme-catalyzed reaction could be detected.