title: Hydration scanning tunneling microscopy of DNA and a bacterial surface protein.
abstract: Hydration scanning tunneling microscopy is based on the electrical conductivity of molecularly thin water layers which adsorb to the sample surfaces in a humid atmosphere. It allows reliable imaging of biological specimens and even insulators, provided they are hydrophilic. Here, we present results obtained with linearized plasmid DNA on mica and a bacterial surface protein layer (the HPI layer). A width of 3 nm was measured for the DNA molecules and a quasi-periodic structure along the molecules with a repeat distance of about 5 nm was observed. We show that-depending on the tunneling voltage-there are two different imaging modes for the DNA samples: at higher voltages, real tunneling or field emission is responsible for the charge transfer between tip and sample. In contrast, at lower voltages we found indications of a water meniscus between tip and surface. The HPI layer, however, seems to be imaged at most voltages without a water meniscus.
authors.affiliation: Department of Structural Biology, Max-Planck-Institut für Biochemie, Martinsried, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Heim
authors.forename: R
authors.initials: R
authors.lastname: Steigerwald
authors.forename: R
authors.initials: R
authors.lastname: Guckenberger
mesh_terms: D000538:Aluminum Silicates; D001426:Bacterial Proteins / Q000648:ultrastructure*; D004247:DNA / Q000648:ultrastructure*; D006095:Gram-Positive Cocci / Q000737:chemistry; D008565:Membrane Proteins / Q000648:ultrastructure*; D016252:Microscopy, Scanning Tunneling; D010957:Plasmids / Q000648:ultrastructure; D014867:Water
chemical_list: D000538:Aluminum Silicates; D001426:Bacterial Proteins; D008565:Membrane Proteins; D014867:Water; D004247:DNA; C011934:mica