Protein-Based Electrical Junctions with Robust Biocompatible Carbon Electrodes Exhibit Activation-less Charge Transport down to 10 K

TL;DR

This study demonstrates a robust, biocompatible protein-based electronic junction with temperature-independent charge transport down to 10 K, enabling stable bio-optoelectronic device integration.

Contribution

It introduces a novel solid-state protein junction with non-invasive carbon electrodes that maintains native protein function and exhibits activation-less charge transport at cryogenic temperatures.

Findings

Electron transport is temperature-independent from 300 K to 10 K.

Green light enhances current via conformational changes, not photoexcitation.

The device maintains protein structure and activity after electrode deposition.

Abstract

The integration of functional proteins into solid-state electronic devices remains a central challenge in molecular bioelectronics due to the fragile nature of protein structures and their complex charge-transport behaviour. Here, we present a robust crosswire evaporated top-contact device based on bacteriorhodopsin (bR) single bilayers (SBL), configured as Au/Cys/bR(SBL)/eC/Au (simplified as Au/bR/eC). The evaporated carbon (eC) top electrode forms a conformal, non-invasive contact that suppresses filament formation and ensures electrical integrity across the cross-wire intersecting area (about 200 micron^2). Structural and spectroscopic analyses confirm that the solid-state bR films maintain the native absorption spectrum and have functional photocycle activity after electrode deposition, implying that their native conformation is not significantly affected. Remarkably, electron transport (ETp) through the 9 nm bR-SBL junctions is temperature-independent within 300 K - 10 K, excluding thermally activated hopping, while the length is incompatible with coherent tunneling. Under green illumination, the junctions exhibit a reversible, photo-induced current enhancement (Jgreen/Jdark = 2), ascribed to light-driven conformational changes rather than direct photoexcitation. The Au/bR/eC architecture thus establishes a thermally non-activated, conformationally mediated transport mechanism via a stable, cryo-compatible solid-state protein junction. This work provides a scalable platform for integrating light-responsive biomolecules into future bio-optoelectronic and neuromorphic devices.