Basic Theory of Dielectrophoresis and Electrorotation Methods for Determining the Forces and Torques Exerted by Nonuniform Electric Fields on Biological Particles Suspended in Aqueous Media

0739-5175/03/$17.00©2003IEEE T he forces exerted by nonuniform ac electric fields can be harnessed to move and manipulate polarizable microparticles—such as cells, marker particles, etc.—suspended in liquid media. Using rotating electric fields, controlled rotation can be induced in these same particles. The ability to manipulate suspended particles remotely without direct contact has significant potential for applications in μTAS (micro total-analysis systems) technology. The nonuniform fields for these particle manipulation and control operations are created by microelectrodes patterned on substrates using fabrication techniques borrowed from MEMS (microelectromechanical systems) technology. A wide variety of structures, ranging from simple planar geometries to complex three-dimensional (3-D) designs, are now under investigation. The implications of these various schemes in certain fields of biotechnology are far-reaching. For example, cells, cellular components, and synthetic marker particles treated with biochemical tags can be collected, separated, concentrated, and transported using microelectrode structures having dimensions of the order of 1 to 100 μm (10−6 to 10−4 m). Furthermore, these forces can manipulate DNA particles, which are several orders of magnitude smaller than cells. This article presents a concise, unifying treatment of the electromechanics of small particles under the influence of electroquasistatic fields and offers a set of models useful in calculating electrical forces and torques on biological particles in the size range from ∼1 to ∼100 μm. The theory is used to consider DEP trapping, electrorotation, traveling-wave induced motion, and orientational effects. The intent is to provide a basic framework for understanding the forces and torques exploited in the research represented by the other articles presented in this special issue of IEEE Engineering in Medicine and Biology Magazine.