Biological Fingerprints in Molecular Electronics
Electron transfer in and across proteins plays a key role in many biological processes of organisms. Fundamental understanding electron flow within protein structures is not only important for biology, but may also help in the design of bio-electronic devices that directly couple to biological systems. Electrochemistry of redox-active proteins and enzymes is widely used to study electron transfer processes in those systems, while the impact of external voltage-driven electronic transport across bio-molecular junctions has been limited because of limited information that could be obtained from resulting current-voltage characteristics. However, as I will show, protein-based molecular junctions can demonstrate distinct transport efficiencies, i.e. junction-currents, depending on protein orientation, conformation, mutation and especially, the presence of cofactors. Molecular junctions with photoactive membrane proteins and photochromic photoreceptor proteins, which alter their conformation upon light absorption, demonstrate modulation in junction-current with illumination. Removing or modifying protein cofactors not only shows direct effects on junction currents, but also a transition from tunneling (temperature-independent) to temperature-dependent transport. The high conducting nature of the protein junctions raises questions about the fundamental nature of electron transport across proteins. Finally, I will demonstrate how these biomolecular signatures from molecular electronic transport can be used to map electron transport paths within the protein. Detailed knowledge of nanoscale conduction pathways would enable developing synthetic proteins with higher conductance and different functionalities, which will directly impact the field of bioelectronics.
 Christopher, B.; Mukhopadhyay, S; Cahen, D; Lederman, D., Towards Bioelectronics with Immobilized Proteins: a review of what we (do not) know. Rep. Prog. Phys. (submitted, arXiv article - 1702.05028)
 Mukhopadhyay, S.; Cohen, S. R.; Marchak, D.; Friedman, N.; Pecht, I.; Sheves, M.; Cahen, D. Nanoscale Electron Transport and Photodynamics Enhancement in Lipid-Depleted Bacteriorhodopsin Monomers ACS Nano, 2015, 137, 11226.
 Mukhopadhyay, S.; Dutta, S.; Pecht, I.; Sheves, M.; Cahen, D. Conjugated Cofactor Enables Efficient Temperature-Independent Electronic Transport Across ∼ 6 nm Long Halorhodopsin. J. Am. Chem. Soc. 2014, 8, 7714.