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

Abstract

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 exible 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 rst time show that it requires about 100 − 120 meV for electrons passing through one heme group inside a hydrated protein molecule.

Deciphering the Roles of Interfacial Amino Acids in Inter-Protein Charge Transport

“…11,54 The activation energy of protein junctions also has a linear relationship with the number of heme groups. 55 Our work provides direct evidence that the location and orientation of heme also play a role that can enhance CT by increasing the coupling strength. In the case of the GG−Cyt c junction, we observe an unusually large value of α Cyt c , deviating from the expected trends of the heme−top electrode distance with α Cyt c and Γ (Figures 2f and 3f).…”

Conductive ionogel for the study of charge transport through SAM-based junctions in aqueous solution

“…1d by the method of AFM as before. 43 We used ultraviolet photoelectron spectroscopy (UPS) to measure the work function of the IG–CB surface to be 4.8 eV as previously reported 43 which is comparable to the work function of polycrystalline Ag (4.7–4.8 eV) and Au (5.0–5.2 eV) (Fig. S4, ESI†).…”

“…45 We have examined the reproducibility and stability of our transport data and we can safely conclude that the migration of carbon black inside the electrode is unlikely to happen, rendering it suitable for prolonged and stable utilization. 43 We speculate that the difference between current density in air and water arises from the affinity of the SAMs and liquid environment. We find that the SAMs of SC 10 in the presence of water result in dramatic decreases in current densities, where the water layer tends to pile up on the surface of SC 10 rather than on the surface of –F or –COOH terminated groups.…”

“…4b and c are similar to our previous studies of cytochrome C by IG–CB electrodes. 43 One of the most prominent advantages of the IG–CB electrode is to measure the activation energy of the protein junction in its native status, that is in physiologically relevant solutions. Fig.…”

“…In our previous work, we have developed a new type of ionogel electrode that has been proven to have excellent stability to be the top electrode both in air and pure water environments and the ability to measure the activation energy of protein junctions as the temperature changes. 43 In this study, we explore our studies to give more choices of aqueous solutions from water to two typical buffer solutions: 0.01 M phosphate buffer saline (PBS) and 0.01 M tris(hydroxymethyl)aminomethane hydrochloride (Tris) buffer solution. We chose three different SAMs with very similar chain length (same number of CH 2 units) but with different terminal groups, which are –COOH, –CH 3 and –F, respectively.…”