Electronic Transport via Proteins

Abstract

A central vision in molecular electronics is the creation of devices with functional molecular components that may provide unique properties. Proteins are attractive candidates for this purpose, as they have specific physical (optical, electrical) and chemical (selective binding, self-assembly) functions and offer a myriad of possibilities for (bio-)chemical modification. This Progress Report focuses on proteins as potential building components for future bioelectronic devices as they are quite efficient electronic conductors, compared with saturated organic molecules. The report addresses several questions: how general is this behavior; how does protein conduction compare with that of saturated and conjugated molecules; and what mechanisms enable efficient conduction across these large molecules? To answer these questions results of nanometer-scale and macroscopic electronic transport measurements across a range of organic molecules and proteins are compiled and analyzed, from single/few molecules to large molecular ensembles, and the influence of measurement methods on the results is considered. Generalizing, it is found that proteins conduct better than saturated molecules, and somewhat poorer than conjugated molecules. Significantly, the presence of cofactors (redox-active or conjugated) in the protein enhances their conduction, but without an obvious advantage for natural electron transfer proteins. Most likely, the conduction mechanisms are hopping (at higher temperatures) and tunneling (below ca. 150-200 K).

Tuning electronic transport via hepta-alanine peptides junction by tryptophan doping

“…Studying electron transport (ETp) via solid-state molecular junctions represents an approach, bridging the study of basic ET-related phenomena and electronic devices, where measuring ET rates as a function of an electrochemical driving force is replaced by measuring current across molecular junctions as a function of an applied electrical voltage (20). Combining the concepts and methods of molecular electronics such as currentvoltage (I-V) line-shape analysis (21,22), temperature-dependent measurements (23,24), and electronic spectroscopy techniques (25)(26)(27) may yield new insights into the mechanism of ETp across the peptide matrix of proteins (28)(29)(30) and pave the road to peptide-and protein-based electronic devices for switching, rectification, and memory (18,31).…”

High-resolution electrochemical STM of redox metalloproteins

“…References [1] and in particular [52,53] include good discussions of how the various processes of electron flow between a protein and its environment (electrode or electrolyte) might be categorised, and point to the distinction between mechanisms involved of 'electron transport' (essentially, protein-mediated electron current between two adjacent metallic contacts) and 'electron transfer' (electrons moving between donor and acceptor sites within a protein, or between a surrounding electrolyte and redox centre in the protein). In all cases however, the driving mechanism is a difference in the electronic electrochemical potential µ, which in EC-STM is tuned by the applied bias between tip and substrate.…”

“…Due to their inherent molecular function and exquisite recognition properties, protein molecules have become a particular focus [57,52,58,59] in recent years. Proteins which are electrically active are of obvious potential for electronic sensing -if they can be linked to external circuitry.…”

Microbial nanowires: an electrifying tale

“…MNWs may also be used in bionanosensors (Lovley et al, 2009); however, no such studies have been reported yet. Interested readers are referred to specific reviews on this topic (Amdursky et al, 2014;Patolsky & Lieber, 2005;Patolsky et al, 2006;Waleed Shinwari et al, 2010;Wang et al, 2014;Ziadan, 2012) which may inform them about how different nanowires, including MNWs, can be used for practical applications.…”