Significance of Nanostructures of an Electrode Surface in Direct Electron Transfer-Type Bioelectrocatalysis of Redox Enzymes

Redox enzymes, which are approximately one-quarter of all known proteins, can be distinguished by their extraordinary activity under mild conditions and wide variety of reaction types. During the last quarter of a century, several attempts have been made to utilize these enzymes as electrocatalysts and develop novel electrochemical systems. The direct electron coupling between redox enzyme reactions and electrode reactions without a redox mediator is known as direct electron transfer (DET)-type bioelectrocatalysis, one of the most intriguing subjects studied in recent decades. In a DET-type system, similar to conventional inorganic catalysts, the enzymes merely function as electrocatalysts. Compared with inorganic catalysts, the distinctive characteristics of redox enzymes include high activity, extremely large size, identity, and uniformity by biological regeneration, versatility, and fragility. Furthermore, the redox site of the enzymes that communicates with electrodes can be rigidly assigned, which clearly defines the redox potential of enzymatic catalysts. These factors lead to characteristic features in DET-type bioelectrocatalytic waves by redox enzymes adsorbed (or immobilized) on a nanostructured electrode surface. This chapter provides an overview, additional insights, and discussion of the recent progress on the control of electrode surfaces for DET-type bioelectrocatalysis while considering the importance of nanostructures of the electrode surface. © 2019 American Chemical Society. All rights reserved.