Scanning Tunneling Microscopy of Biological Molecules on Pt(111): From 100 to 5 × 10⁶ Da

We have performed ultrahigh vacuum (UHV) scanning tunneling microscopy studies of biological molecules by developing a UHV compatible cell wherein a drop of ultrapure water containing nanograms of molecules is evaporated from a strongly chemisorbing Pt(111) surface in an Ar ambient. Images are presented for hydroquinone; oligomers including pentaphenyl ether, enkephalin, and sodium dodecyl sulfate; large homopolymers of lysine and glycine; the proteins calmodulin, tropomyosin, and immunoglobin G; and double- and single-stranded plasmid DNA. In all cases the apparent height is only a few Å. Imaging properties understandably vary from clearly resolved internal molecular structure for hydroquinone to diffuse, artifact-prone images for molecules which exceed tens of angstroms in thickness. These data do not support claims for atomic resolution imaging of complex biomolecules. © 1993, American Chemical Society. All rights reserved.