Single-Entity Bioelectrochemistry

Abstract

Interfacing biological catalytic entities, such as whole cells or enzymes, with electrodes, has a wide range of applications, ranging from fundamental studies of the entities themselves to power generation, bioremediation, chemical synthesis, and biosensing. In all cases, the operation of these bioelectrocatalytic systems is based on electron transfer phenomena within protein molecules, whether isolated or residing inside cells or parts of cells, as well as between proteins and electronics. Typically, the electron transfer and catalytic properties of proteins are studied using ensemble averaging methods, which obscure any heterogeneity and dynamics of individual molecules. This information, however, is especially important for understanding electron transfer and catalytic processes within a living cell where only one or a few protein molecules are present. While single-entity electrochemical measurements are particularly useful for studying electron transfer reactions at the nanoscale level, they have limited applications for investigating biological entities due to the experimental challenges associated with direct measurements of small electrical currents. 1,2 Here we will discuss our recent progress in investigating biological electron transfer reactions at the single-entity level, from bacterial cells to single redox proteins, using nano-impact (collision) single-entity electrochemistry. 3 We demonstrate how advances in electrode fabrication methods and detection setups enable current detection in the fA range. When combined with the developed data processing algorithm based on unsupervised learning and template matching techniques, this enabled unprecedented insight into electron transfer processes at the nanoscale. We will talk about insights provided by the method in the study of several important bioelectrocatalytic systems: single E.coli cells with overexpressed Fe-Fe hydrogenases, single bilirubin oxidase molecules, and single catalase molecules. In addition, we will discuss models that we developed for understanding the single bioentity electrode interactions for diffusion-controlled enzymes when the product of the catalytic reaction is detected on the electrode, as well as systems based on direct electron transfer between the bioentity and the electrode. Overall, we show how single-entity bioelectrochemistry can shed light on biological electron transfer and catalysis processes and discuss the challenges it currently faces. Zhang, J.-H.; Zhou, Y.-G. Nano-Impact Electrochemistry: Analysis of Single Bioentities. TrAC Trends Anal. Chem. 2019, 115768.Davis, C.; Wang, S. X.; Sepunaru, L. What Can Electrochemistry Tell Us About Individual Enzymes? Curr. Opin. Electrochem. 2020, 100643.Sekretaryova, A. N.; Vagin, M. Yu.; Turner, A. P. F.; Eriksson, M. Electrocatalytic Currents from Single Enzyme Molecules. J. Am. Chem. Soc. 2016, 138 (8), 2504–250