Current rectification via Photosystem I monolayers induced by their orientation on hydrophilic self-assembled monolayers on titanium nitride

TL;DR

This study demonstrates current rectification in Photosystem I monolayers oriented on hydrophilic self-assembled monolayers on titanium nitride, offering a new approach for biomolecular electronics with potential for optoelectronic applications.

Contribution

It introduces a simple bottom-up fabrication method to immobilize oriented PSI monolayers on titanium nitride, enabling rectification studies and future optoelectronic device integration.

Findings

Achieved current rectification ratios of up to ~200.

Measured work function shifts to investigate rectification mechanisms.

Provided a platform for embedding PSI in solid-state optoelectronic devices.

Abstract

Photosystem I (PSI) is a photosynthetic protein which evolved to efficiently transfer electrons through the thylakoid membrane. This remarkable process attracted the attention of the biomolecular electronics community, which aims to study and understand the underlying electronic transport through these proteins by contacting ensembles of PSI with solid-state metallic contacts. This paper extends published work of immobilizing monolayers of PSI with a specific orientation, by using organophosphonate self-assembled molecules with hydrophilic heads on ultra-flat titanium nitride. Electrical measurements carried out with eutectic GaIn top contacts showed current rectification ratios of up to ~200. The previously proposed rectification mechanism, relying on the protein's internal electric dipole, was inquired by measuring shifts in the work function. Our straightforward bottom-up fabrication method may allow for further experimental studies on PSI molecules, such as embedding them in solid-state, transparent top contact schemes for optoelectronic measurements.