Enzyme-catalyzed direct electron transfer: Fundamentals and analytical applications

This article overviews the fundamentals of the phenomenon of direct electron transfer in enzyme-catalyzed electrode reactions and the development of electroanalytical applications of the bioelectrocatalytic systems. A brief description of the enzymes capable of catalyzing electrochemical reactions by means of direct electron transfer is given. The physico-chemical background of bioelectrocatalysis is discussed in terms of the different concepts underlying the mechanism of electron transfer. The concept of a ''molecular transducer'' is introduced to designate a complex, formed by the electrocatalytically active enzyme on the electrode-electrolyte interface, which is directly responsible for the transduction of the chemical signal to an electric one. The role of this ''molecular transducer'' in enzyme electrodes and immunoelectrodes is discussed. The analytical applications of bioelectrocatalysis are categorized as systems employing either amperometric or potentiometric detection. Discussion focuses on the advantages of systems based on enzyme-catalyzed direct electron transfer as opposed to other enzyme-catalyzed electroanalytical devices. In conclusion, the trends towards upcoming practical applications are suggested as well as some directions in fundamental studies of bioelectrocatalysis as a phenomenon.