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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°), 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