Electron transport properties of helical peptide dithiol at a molecular level: Scanning tunneling microscope study

Electron transport properties of a helical peptide dithiol were investigated by using scanning tunneling microscopy under ultrahigh vacuum. A helical peptide, which carries two thiol moieties at both terminals but with different protecting groups, was synthesized. One terminal was deprotected and was incorporated into defects of the pre-assembled dodecanethiolate monolayer on gold. Then, the other terminal was deblocked to bind with gold nanoparticles, resulting in formation of metal-molecule-metal junction. Current-distance measurement of gold-peptide dithiol-gold nanoparticle by scanning tunneling microscopy clearly showed a plateau region in the current response, indicating the physical contact of the tip with the gold nanoparticle. Keeping this contact, current-voltage measurement was carried out to show a rectification behavior. The enhancement of electron transport at the negative bias can be explained by taking the dipole effect of the helical peptide into consideration.