Scanning Tunneling Microscopy of a Hydrated Bacterial Surface Protein

Abstract Imaging of biological macromolecules by scanning tunneling microscopy is hampered by the poor electrical conductivity of these objects. We found, however, that by controlling the protein hydration a small but sufficient conductivity can be induced. At tunneling currents lower than 0.5 pA and tunneling voltages up to 10 V and at a humidity in the range between 30% and 45% it was possible to obtain clear images of the HPI layer, a protein which naturally forms a two-dimensional ordered array on a bacterial surface.