title: STM of metal embedded and coated DNA and DNA-protein complexes.
abstract: Bare and Pt/Ir/C-coated DNA has been analysed using scanning tunnelling microscopy (STM). To achieve reproducible imaging of bare DNA on mica ethanol/air-dried molecules were embedded in Pt/C. By peeling the metal film off the mica, the previously mica-exposed side of the Pt/C-film with the embedded DNA molecules was accessible for STM analysis. By applying this replica/anchoring technique only hollow trenches in the metal film, and not the DNA itself, could be visualized. The gaps averaged 3.1 nm (+/- 0.9 nm) wide and 1 nm (+/- 0.5 nm) deep. Using scanning force microscopy it could be confirmed that the DNA remained in the Pt/C film during the peel-off procedure. For STM, DNA fragments were also coated with 0.7-1 nm Pt/Ir/C. Owing to the high Z-resolution the STM samples were coated at a high elevation angle (65 degrees), thereby minimizing the problem of self-shadowing. Coating by Pt/Ir/C allowed routine imaging and quantitative analysis of both ethanol/air- and freeze-dried DNA under atmospheric conditions. After ethanol/air drying measured values for DNA width and height were 5.1 nm (+/- 1.8 nm) and 0.9 nm (+/- 0.2 nm), respectively. Freeze-dried DNA averaged 4.2 nm (+/- 1.3 nm) wide and 1.1 nm (+/- 0.1 nm) high. A Pt/Ir/C-coating was also applied to visualize DNA-protein interaction using STM.
authors.affiliation: Eidgenössische Technische Hochschule, Institut für Zellbiologie, ETH-Hönggerberg, Zürich, Switzerland.
authors.forename: T
authors.initials: T
authors.lastname: Müller-Reichert
authors.forename: H J
authors.initials: HJ
authors.lastname: Butt
authors.forename: H
authors.initials: H
authors.lastname: Gross
mesh_terms: D000538:Aluminum Silicates; D004247:DNA / Q000648:ultrastructure*; D004268:DNA-Binding Proteins / Q000648:ultrastructure*; D004926:Escherichia coli / Q000737:chemistry; D006108:Graphite; D007495:Iridium; D018625:Microscopy, Atomic Force / Q000379:methods; D016252:Microscopy, Scanning Tunneling / Q000379:methods*; D010984:Platinum
chemical_list: D000538:Aluminum Silicates; D004268:DNA-Binding Proteins; D007495:Iridium; D010984:Platinum; D006108:Graphite; D004247:DNA; C011934:mica