Probing electron transport in proteins at room temperature with single-molecule precision.

Studying electron transport through immobilized proteins at the single-molecule level has been of interest for more than two decades, with a view on the fundamentals of charge transport in condensed media and applications in bioelectronics. Scanning tunneling microscopy (STM) is a powerful tool in this context, because, at least in principle, it should be possible to address individual proteins on an electrode surface reproducibly with single-protein precision. As reported in this issue of ACS Nano, MacDonald and colleagues have now achieved this for the first time at room temperature for covalently immobilized cytochrome b562, combining imaging and tunneling spectroscopy in a custom-built, ultralow drift STM, with single-protein precision. Using site-directed mutagenesis, cysteines introduced in specific locations in the amino acid sequence of the protein allowed the team to investigate conduction along different directions through the protein, namely along its short and long axes.