AC Electrokinetic techniques such as dielectrophoresis [1,2] and electrorotation  have been utilised for many years for the manipulation, separation and analysis of cellular-scale particles. The phenomenon occurs due to the interaction of induced dipoles with dynamic electric fields, and can be used to exhibit a variety of motions including attraction, repulsion and rotation by changing the nature of the dynamic field.
Recent advances in semiconductor manufacturing technology have enabled researchers to develop electrodes for manipulating macromolecules as small as 9kDa using both attractive  and repulsive  AC electrostatic forces, and to concentrate 14nm beads from solution . Trapping of single particles such as viruses and 93nm-diameter latex spheres in contactless potential energy wells  has also been demonstrated. AC Electrokinetics offers advantages over scanning-probe methods of nanoparticle manipulation in that the equipment used is simple, cheap and has no moving parts, relying entirely on the electrostatic interactions between the particle and dynamic electric field. Furthermore, there is theoretical evidence that as manufacturing technology further improves, single particles considerably smaller than presently studied using AC Electrokinetics may be manipulated.
Ultimately, such a technology will have obvious applications for the manipulation of single molecules. Previous studies [4,7] have shown that the trapping efficiency of planar electrode arrays is dependent on a number of factors including the magnitude and dimensions of the electric field and the radius of the particle to be trapped. In this paper we will consider the ways in which AC Electrokinetics can benefit nanotechnology, and the constraints on the technique due to factors such as Brownian motion, heating of the medium, and electrode dimensions as the electrode array is miniaturised to the nanometre scale.
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Michael Pycraft Hughes
European Institute of Health and Medical Sciences/School of Mechanical and Materials Engineering,
University of Surrey Guildford, Surrey, GU2 5XH, United Kingdom
Tel: +44 1483 300800; Fax: +44 1483 306039