Ionogel-Electrode for the Study of Protein Tunnel Junctions under Physiologically Relevant Conditions

The study of tunneling through proteins is essential for the understanding of complicated electrochemical processes in biological activities. Both electron transport and transfer phenomena are found in protein junctions, but the reason remains unknown. In this work, we polymerized an ionic liquid into a conductive and flexible electrode, and used it as a top-contact to form highly reproducible molecular junctions of protein molecules on a silver bottom-electrode. The junctions of proteins, choice of which including human serum albumin, cytochrome C or hemoglobin, show temperature independent electron transport characteristics, when junctions are in solid states; but all junctions can be switched to temperature dependent electron transfer, when junctions are hydrated in water. We experimentally for the first time show that it requires about 100 − 120 meV for electrons passing through one heme group inside a hydrated protein molecule.