Single-Protein Electronics—Charge Transport Mechanisms and Enzymatic Junctions

Bioelectronics is a rapidly evolving field moving towards designing nanoscale electronic platforms that allow <i>in vivo</i> sensing, fuel cell powering and chemical biosynthesis. Such devices typically require interfacing a complex biomolecular moiety as the active component to an electronic platform for signal transduction and/or electron source wiring. Inevitably, a true systematic design goes through a bottom-up understanding of the structurally related electrical signatures of such hybrid biomolecular circuits, which will ultimately lead us to tailor its electrical properties and exploit them as high performance bioelectronic devices with a wide variety of applications in organic electronics, sensing, biomanufacturing, <i>etc</i>.<br/><br/>In this contribution, we will present our latest efforts on understanding and control charge transport in a single-protein junction, with an emphasis on how to harness enzymatic activity electrically in an individual enzyme. Our approach relies on trapping individual redox proteins in an electrochemically controlled tunneling junction to characterize their main electrical signatures. The method can capture very fine details of the charge transport mechanisms across proteins in an aqueous environment [1,2].<br/><br/>Our studies start with a benchmark redox protein model such as a bacterial blue Cu-Azurin. We will show first the main observed electrical signatures of these systems that make them particularly efficient in transporting charge. We then bioengineer the outer protein surface using point-site mutagenesis as a mean to get a more detailed picture of possible electron pathways through the protein backbone [2,3]. Our results suggest that the protein might not use distinct physical electron pathways across its structure, but transport mechanism can be switched upon quenching of motions in the protein structure via the surface mutations.<br/><br/>Then, we will then switch to our very recent charge transport studies on redox enzymes. Using the above electrochemically controlled single-protein methodologies, we demonstrate that when an individual redox enzyme is trapped on a nanoscale junction, a distinct telegraphic noise can be directly correlated to the enzymatic activity of the enzyme during the active bioelectrocatalytic conditions [4]. This study open a new door for the fundamental studies of redox enzymatic catalysis and brings prospects to the high-resolution electrical detection of enzymatic reactions.<br/><br/><br/>1. A.C. Aragonès <i>et al.</i> Small, 10, 2537 (2014).<br/>2. M.P. Ruiz <i>et. al.</i> JACS 139, 15337 (2017).<br/>3. M.P. Ruiz <i>et al.</i> <i>in preparation</i> (2023).<br/>4. T. Ha <i>et al.</i> <i>in preparation</i> (2024).