Single-molecule mapping of long-range electron transport for a cytochrome b(562) variant

Cytochrome b(562) was engineered to introduce a cysteine residue at a surface-exposed position to facilitate direct self-assembly on a Au(111) surface. The confined protein exhibited reversible and fast electron exchange with a gold substrate over a distance of 20 Å between the heme redox center and the gold surface, a clear indication that a long-range electron-transfer pathway is established. Electrochemical scanning tunneling microscopy was used to map electron transport features of the protein at the single-molecule level. Tunneling resonance was directly imaged and apparent molecular conductance was measured, which both show strong redox-gated effects. This study has addressed the first case of heme proteins and offered new perspectives in single-molecule bioelectronics.