Observation of single helical peptide molecule incorporated into alkanethiol self-assembled monolayer on gold by scanning tunneling microscopy

The bicomponent self-assembled monolayers (SAMs) were formed by incorporation of helical peptides into the alkanethiol monolayer, which was prepared in advance on gold substrate, and were characterized by Fourier transform infrared reflection-absorption spectroscopy (FTIR RAS) and scanning tunneling microscopy (STM). FTIR RAS spectra showed that the helical peptides were incorporated into the defects in the alkanethiol SAM without disturbing the film structure. A single helical peptide molecule was observed clearly in the bicomponent SAMs by STM. Several helical peptides associated together in a parallel arrangement to form a helix-bundle structure. Observation of the long molecule of ∼4 nm length standing vertically on the surface indicated that electron transfer occurred over a long distance through the helical peptide under the STM conditions.