Electronic Transport Through Organophosphonate-Grafted Bacteriorhodopsin Films on Titanium Nitride

Understanding the charge transport properties of proteins at the molecular scale is crucial for the development of novel bioelectronic devices. In this contribution, we report on the preparation and electrical characterization of thin films of bacteriorhodopsin grafted on the surface of titanium nitride via aminophosphonate linkers. Thickness analysis using atomic force microscopy revealed a protein film thickness of 8.2±1.5 nm, indicating the formation of a protein bilayer. Electrical measurements were carried out in the dry state, in a vertical arrangement with a eutectic gallium-indium (EGaIn) or an evaporated Ti/Au top contact. DC current-voltage measurements yielded comparable effective tunneling decay constants $\beta\sim 0.13\mathrm{A}^{-1}$ for the EGaIn top contact and $\sim 0.15\mathrm{A}^{-1}$ for the Ti/Au top contact. The results presented herein may establish a novel platform for studying charge transport via protein molecules in a solid-state device configuration.