Executive Summary : | The functional versatility that evolution imparted on proteins rationalizes the interest in their electronic charge-carrying properties for biomolecular electronics. If the charge transport properties of these building blocks of nature can be fully understood and controlled, great opportunities open up for integrating proteins into possible future biomolecular electronic devices. The last two decades have seen a great effort has been made to fabricate device architectures with protein molecules acting as functional components such as diodes, transistors, and switches. The current understanding of the ETp mechanism via proteins envisions two major mechanisms: coherent tunneling and incoherent vibrationally-assisted hopping. To date, temperature-independent (activation-less) transport has been observed in more than three proteins that are longer than 5 nm, viz. halorhodopsin (~6.0 nm), bacteriorhodopsin (~ 6 nm), photosystem 1 (~ 7 nm), and ferritin (~ 10 nm). This finding is surprising given the distances of electron transport through these proteins (greater than 5 nm). The mechanism(s) and structural basis of this high-efficiency tunneling over long distances are unknown and at the proposed research’s focus. This indicates that our fundamental knowledge of charge transport processes between short-distance tunneling and long-distance hopping via solid-state protein molecules is limited. This proposal aims to understand what ETp mechanism(s) enables efficient conduction via solid-state single-protein junctions over long distances. A AuNP dimer structure connected by a single protein (AuNP-Protein-AuNP) is synthesized and then dielectrophoretically trapped into high-resolution e-beam lithography (EBL) nanofabricated device architectures. Current-Voltage-Temperature (10 K-340 K), conductance-voltage, and Inelastic Electron Tunneling Spectroscopy (IETS) experiments at cryogenic temperatures will be carried out to elucidate the ETp mechanism. In addition, gating (by introducing gate voltage (VG)) measurements will also be carried out on the same junction configuration but using different experimental set-ups. The project aims to perform experiments, designed to test/challenge the models and their predictions, especially for trends, concerning the dependence on temperature and contacts (electrode-protein coupling) of transport efficiency across protein mono-layers greater than 5 nm. Gating experiments will add further information regarding the energy landscape of proteins embedded between two AuNPs, providing the missing link between the energetics and the ETp mechanism via single-protein junctions. The experiments proposed here look beyond the traditional state-of-the-art research and offer a versatile platform for the investigation of single-protein-based biological functions which might lead to the large-scale manufacture of integrated bioelectronic circuits. |