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Frequency and Voltage Dependence of the Dielectrophoretic Trapping of Short Lengths of DNA and dCTP in a Nanopipette

Liming Ying ^*, Samuel S. White ^*, Andreas Bruckbauer ^*, Lisa Meadows , Yuri E. Korchev  and David Klenerman ^*

^* Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, United Kingdom; Department of Genetics, University of Cambridge, Cambridge, CB2 1GA, United Kingdom; and MRC Clinical Science Center, Division of Medicine, Imperial College School of Medicine, London, W12 0NN, United Kingdom

Correspondence: Address reprint requests to David Klenerman, Tel.: +44-1223-336481; Fax: +44-1223-336362; E-mail: dk10012{at}cam.ac.uk.

The study of the properties of DNA under high electric fields is of both fundamental and practical interest. We have exploited the high electric fields produced locally in the tip of a nanopipette to probe the motion of double- and single-stranded 40-mer DNA, a 1-kb single-stranded DNA, and a single-nucleotide triphosphate (dCTP) just inside and outside the pipette tip at different frequencies and amplitudes of applied voltages. We used dual laser excitation and dual color detection to simultaneously follow two fluorophore-labeled DNA sequences with millisecond time resolution, significantly faster than studies to date. A strong trapping effect was observed during the negative half cycle for all DNA samples and also the dCTP. This effect was maximum below 1 Hz and decreased with higher frequency. We assign this trapping to strong dielectrophoresis due to the high electric field and electric field gradient in the pipette tip. Dielectrophoresis in electrodeless tapered nanostructures has potential applications for controlled mixing and manipulation of short lengths of DNA and other biomolecules, opening new possibilities in miniaturized biological analysis.

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