Articles you may be interested inThe authors investigate the elongation and orientation of different-sized deoxyribose nucleic acid (DNA) molecules, tethered onto gold electrodes via a terminal thiol, under the influence of high frequency ac electric fields. The DNA molecules are elongated from a random coil into an extended conformation and orientated along the electric field lines as a result of the forces acting on the molecules during the application of the ac electric fields. Elongation was observed in the frequency range 100 kHz-1 MHz, with field strengths of 0.06-1.0 MV/ m. Maximum elongation for all DNA fragments tested, irrespective of size, was found for frequencies between 200 and 300 kHz. The torque acting on the induced dipole in the DNA molecules, complemented by a directional bias force, opposite in direction to the dielectrophoretic force, provides the main contribution to the elongation process. The length of elongation is limited to either half the distance between opposing electrodes or to the contour length of the DNA, whichever is shorter. Further, the authors show that the normalized length of the elongated DNA molecules is independent of the contour length of the DNA.

We report three-dimensional imaging measurements using confocal microscopy of fluorescently labelled deoxyribonucleic acid ͑DNA͒ 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.

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The controlled manipulation of molecules is a crucial prerequisite for the emerging field of molecular nanotechnology. AC electrokinetics provide a powerful mechanism for both positioning and inducing conformational changes in molecules. In this paper, we investigate the elongation of fluorescently-labelled DNA strands, which are covalently tethered by one end to gold microelectrodes arranged in an opposing-finger geometry, when exposed to strong ac electric fields. We found that the elongation of the DNA molecules is restricted by the geometry of the gap, and that the observed contour of the elongated DNA molecules coincides with the electric field line pattern. Further, we discuss a potential elongation mechanism and provide evidence that the major contribution to the elongation originates from the ac electrokinetic torque, which is supplemented by a small bias force provided by the electric-field-induced fluid flow.

A tunable universal terahertz filter using artificial dielectrics based on parallel-plate waveguides Appl. Phys. Lett. 97, 131106 (2010); 10.1063/1.3495994Electromagnetic simulation of terahertz frequency range filters for genetic sensing