Charge transport at the protein–electrode interface in the emerging field of biomolecular electronics

Abstract The emerging field of BioMolecular Electronics aims to unveil the charge transport characteristics of biomolecules with two primary outcomes envisioned. The first is to use nature’s efficient charge transport mechanisms as an inspiration to build the next generation of hybrid bioelectronic devices towards a more sustainable, biocompatible, and efficient technology. The second is to understand this ubiquitous physicochemical process in life, exploited in many fundamental biological processes such as cell signalling, respiration, photosynthesis, or enzymatic catalysis, leading us to a better understanding of disease mechanisms connected to charge diffusion. Extracting electrical signatures from a protein requires optimised methods for tethering the molecules to an electrode surface, where it is advantageous to have precise electrochemical control over the energy levels of the hybrid protein-electrode interface. Here, we review recent progress towards understanding the charge transport mechanisms through protein-electrode-protein junctions, which has led to the rapid development of the new BioMolecular Electronics field. The field has brought a new vision into the molecular electronics realm, where complex supramolecular structures such as proteins can efficiently transport charge over long distances when placed in a hybrid bioelectronic device. Such anomalous long-range charge transport mechanisms acutely depend on specific chemical modifications of the supramolecular protein structure and on the precisely engineered protein-electrode chemical interactions. Key areas to explore in more detail are parameters like protein stiffness (dynamics) and intrinsic electrostatic charge, and how these influence the transport pathways and mechanisms in such hybrid devices.