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High Resolution DNA Imaging by Atomic Force Microscopy

Dmitry Klinov
Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia

Unique resolution was demonstrated in tapping mode and point contact atomic force microscopy of DNA molecules using new diamond-like carbon probes with a ~ 1nm extremity. The probes were prepared by a plasma-assisted growth of carbon spikes at the apex of conventional Si probes. The probes were grown at the apex of Si probes, which are usually applied in atomic force microscopy. TEM micrographs of one of the probes (Figure a) show differently oriented carbon spikes grown at the Si tip. The most advanced spike with the ~ 1 nm extremity can be used for AFM imaging. A tip apex of etched Si probes used in tapping mode is typically in the 10-20 nm range. The resolution in tapping mode images is higher than the apex size that is most likely related to the fact that tip-sample contact area depends not only on the tip size but also on imaging force and mechanical properties of the sample and the tip. Ambient imaging of the DNA molecules with the diamond-like carbon and Si probes showed that fine structural resolution is achieved only by using the sharp diamond-like carbon probes (Figure b). The images obtained with this probe reproduce the helical pitches and Z-like kinks on the DNA molecules.
Conductivity of native DNAs of course will depend on many factors, such as the contacts to the electrodes [1], the procedure of deposition [2]. Different types of kinks and bendings that is not resolved by using conventional Si probes can also decrease conductivity of DNAs. Images of DNA molecules obtained with these probes (Figure b) exhibit high-resolution.

(a) TEM micrographs of the new diamond-like carbon probes at different magnifications, (b) AFM image of DNA molecules with the new diamond-like carbon probe on the mica.

1. Kasumov A., Kociak M., Gueron S., Reulet B., Volkov V., Klinov D., and Bouchiat H., Science, 291, 280-282 (2001).
2. Kasumov A., Klinov D, Roche P.-E., Gueron S., and Bouchiat H., Applied physics letters, 84 (6), 1007-1009 (2004).