Protein imaging on a semiconducting substrate: a scanning tunnelling microscopy investigation

The reverse transcriptase (RT) enzymes of the human immune deficiency virus 1 (HIV-1) and of the avian myeloblastosis virus (AMV) are deposited onto the semiconducting substrate n-MoTe2 and imaged by scanning tunnelling microscopy (STM). Molecule selection was made after considering the unique complex and specific enzyme structures and medical relevance. Protein immobilization is attributed to specific substrate structural defects and localized electrostatic interaction. The ultrastructure resolution obtained is ascribed to energetic and charge transfer properties of metal tip/protein/semiconductor contacts with an energetic shift of semiconductor band edges due to (partial) Fermi level pinning and/or formation and reversal of a strong inversion layer. Protein electron transport combining Poole–Frenkel-type transport in insulators and solvation-induced electron detrapping is suggested.