Amperometric Enzyme Sensors based on Direct and Mediated Electron Transfer

Abstract

Publisher Summary The simplest design of an amperometric biosensor is the direct measurement of either an enzymatically generated product or of an electron transfer (ET) mediator naturally involved in the biocatalytic process. For a principal understanding of the ET processes underlying the functionality of all amperometric biosensors, the theoretical background is used as it was developed for the elucidation of ET processes that play a vital role in a variety of biological reactions or in artificial “donor–acceptor system”. These donor–acceptor reactions can be very rapid even when the reactants are separated over longer distances. This chapter presents a brief summary of the Marcus-theory of ET and also focuses on the fabrication of suitable biosensor architectures facilitating electrochemical communication between the immobilized redox proteins and the electrode surface. The chosen immobilization technique and its impact on the biological recognition element affects, significantly, the overall biosensor performance and determines the selectivity, sensitivity, specificity, dynamic range, response time, and reliability of the biosensor. Several techniques for the immobilization of redox protein on electrode surfaces have been described in detail. In order to control the fabrication and later, function of an amperometric biosensor to its largest extent, the development of the so-called “reagentless biosensors” is of increasing importance. For the development of a reagentless biosensor, the most appropriate methods are the use of an enzyme with tightly bound redox centers and an ET pathway either by direct ET or via securely immobilized redox relays.