Micro‐ and Nanoscopic Imaging of Enzymatic Electrodes: A Review

International audienceRedox enzymes, that catalyze electron transfer reactions in living organisms, can be used as selective and sensitive bioreceptors in biosensors, or as efficient catalysts in biofuel cells. In these bioelectrochemical devices, the enzymes are immobilized at a conductive surface, the electrode, with which they must be able to exchange electrons. Different physico-chemical methods have been coupled to electrochemistry to characterize the enzyme-modified electrochemical interface. In this review, we summarize most efforts performed to investigate the enzymatic electrodes at the micro and even nanoscale thanks to microscopy techniques. Contrary to electrochemistry, which gives only a global information about all processes occurring at the electrode surface, microscopy offers a spatial resolution. Several techniques have been implemented: mostly scanning probe microscopy like atomic force microscopy (AFM), scanning tunneling microscopy (STM) and scanning electrochemical microscopy (SECM), but also scanning electron microscopy (SEM) and fluorescence microscopy. These studies demonstrate that various information can be obtained thanks to microscopy at different scales. Electrode imaging has been performed to confirm the presence of enzymes, to quantify and localize the biomolecules, but also to evaluate the morphology of immobilized enzymes, their possible conformation changes upon turnover, and their orientation at the electrode surface. Local redox activity has also been imaged and kinetics has been resolved.Introductio