Establishment of the ac electrokinetic elongation mechanism of DNA by three-dimensional fluorescent imaging

Abstract

We report three-dimensional imaging measurements using confocal microscopy of fluorescently labelled deoxyribonucleic acid (DNA) strands subjected to strong ac electric fields. The DNA molecules are covalently tethered by one end to gold microelectrodes and the observed elongation patterns are compared with the electric field lines obtained from numerical simulations and with previously determined fluid flow patterns. We demonstrate that the major contribution to the elongation stems from the ac electrokinetic torque, supplemented by a small bias force provided by the electric-field-induced fluid flow, and we provide evidence that the observed restricted elongation owing to the geometries of the electrodes results from a sign change in the bias force.