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

The study of charge transport through proteins is essential for understanding complicated electrochemical processes in biological activities while the reasons for the co-existence of tunneling and hopping phenomena in protein junctions still remain unclear. In this work, we synthesized a flexible and conductive ionogel electrode and used it as a top contact to form highly reproducible protein junctions. The junctions of proteins, including human serum albumin, cytochrome C and hemoglobin, show temperature-independent electron tunneling characteristics when junctions are in solid states while with a different mechanism of temperature-dependent electron hopping when junctions are hydrated under physiologically relevant conditions. We demonstrate the solvent reorganization energy plays an important role in the electron hopping process and for the first time, experimentally show that it requires ∼100 meV for electrons hopping through one heme group inside a hydrated protein molecule connected between two electrodes. This article is protected by copyright. All rights reserved.