STM imaging of proteins on semiconducting substrates

The enzyme reverse transcriptase (RT) of the human immunodeficiency virus (HIV) is imaged by scanning tunnelling microscopy (STM). RTs are selected due to their highly specificstructure and their biochemical and medical relevance. The enzymes are deposited on layered semiconducting MoTe2. Structural defects on the substrate surface are suggested to attach the biomolecules due to electrostatic forces. The STM images clearly show the structure of the protein in excellent agreement with structural predictions from small angle neutron scattering and X-ray diffraction measurements. The high resolution imaging process is discussed with regard to the STMmetal tip / protein / semiconductor junction energetics.Resonant electron tunnelling is ascribed to an overlap of semiconductor conduction band and extended LUMO states of theenzyme. Within the biomolecule, electron transfer is suggestedto occur via Poole-Frenkel mechanism in combination with electron release due to solvation shell fluctuations.