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High currents in DNA by the standing DNA method

Direct electrical transport measurements on a complex sequence of 26 base-pair double-stranded DNA showed high currents (220 nA@2V) [1,2]. These experiments were performed when the ssDNA molecules are arranged in a mono-layer on a gold surface. Some of them hybridise to a complementary strand that is attached to gold nanoparticles at the opposite ends and no non-specific interaction along the molecule with a hard surface occurs. A conductive AFM tip is utilized to both scan the sample and contact the gold nanoparticles that are connected to the surface through the dsDNA. A comprehensive set of control experiments, including I-V curves obtained while stretching the DNA molecules, confirms these results. The results of these experiments have been recently published [1]. Further experiments utilizing this experimental method are under way to characterize sequences of varying length, sequence and of G4-DNA.

Further measurements were performed on mono-layers of ssDNA, dsDNA connected with thiols only on one end to the surface and on dsDNA thiolated on both ends. These measurements were done without the gold nanoparticles, confirmed the above results and demonstrated the crucial role of the covalent attachment of the molecules to the electrodes [2].

[1] H. Cohen, C. Nogues, R. Naaman, D. Porath, "Direct measurement of electrical transport through single DNA molecules of complex sequence", Proc. Natl. Acad. Sci. USA 102, 11589 (2005).
[2] Hezy Cohen, Claude Nogues, Daniela Ullien, Shirley Daube, Ron Naaman and Danny Porath, "Electrical characterization of self-assembled single- and double-stranded DNA monolayers using conductive AFM", Faraday Discussions (with volume cover) 131, 367 (2006).

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