Abstract
Redox enzymes, which catalyze reactions involving electron transfers in living organisms, are very promising components of biotechnological devices, and can be envisioned for sensing applications as well as for energy conversion. In this context, one of the most significant challenges is to achieve efficient direct electron transfer by tunneling between enzymes and conductive surfaces. Based on various examples of bioelectrochemical studies described in the recent literature, this review discusses the issue of enzyme immobilization at planar electrode interfaces. The fundamental importance of controlling enzyme orientation, how to obtain such orientation, and how it can be verified experimentally or by modeling are the three main directions explored. Since redox enzymes are sizable proteins with anisotropic properties, achieving their functional immobilization requires a specific and controlled orientation on the electrode surface. All the factors influenced by this orientation are described, ranging from electronic conductivity to efficiency of substrate supply. The specificities of the enzymatic molecule, surface properties, and dipole moment, which in turn influence the orientation, are introduced. Various ways of ensuring functional immobilization through tuning of both the enzyme and the electrode surface are then described. Finally, the review deals with analytical techniques that have enabled characterization and quantification of successful achievement of the desired orientation. The rich contributions of electrochemistry, spectroscopy (especially infrared spectroscopy), modeling, and microscopy are featured, along with their limitations.
Highlights
Interest in and Limitation of Bioelectrocatalysis Based on Immobilized Redox Enzymes1.1
The goal of the present review is to describe these specific aspects, and it will focus on the main parameters that govern the functional immobilization of redox enzymes on electrodes, as well as the current tools available to rationalize and control these parameters
The expression for the Electron Transfer (ET) rate the constant of electron transfer through tunneling, and d the thickness of the SAM. This is the case constant can be read as ktunnel = k° exp[−βd], where k° is the rate constant for a bare electrode, β is the for chemisorption of long-chain thiols on a gold surface, which usually results in well-organized constant of electron transfer through tunneling, and d the thickness of the SAM
Summary
Electron Transfer (ET) is an essential process allowing a variety of microorganisms to find energy for growth. Many of these individual proteinsanother and enzymes be environment or on theand typemetal of microorganism, one protein can replace one as can electron donor identified, and fully characterized in vitro. The way they interact in vivo to fulfill the ET chain, or acceptor for a specific process. Respiration of some exotic microorganisms known as extremophiles is (plastocyanin), on the one hand, and FeS cluster- or flavin mononucleotide-containing proteins pertinent in this respect (Figure 1A) The latter are very interesting because they are (flavodoxin), on the other hand, act as electron transfer shuttles allowing the coupling of water sources of enzymes exhibiting outstanding properties, such as to high temperatures,. Requires as a first step the immobilization of the proteins or enzymes on conductive solid surfaces which act as electrodes, with the ultimate goal of keeping the protein structure as functional as possible
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