Electrokinetic behaviour of colloidal particles in travelling electric fields: studies using yeast cells

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Abstract
Suspensions of yeast cells (Saccharomyces cerevisiae) were used as model systems to investigate the electrokinetic behaviour of colloidal particles subjected to travelling electric fields generated using microelectrodes. Measurements were made over the frequency range 1 kHz to 10 MHz and for suspending medium conductivities in the range 6-260 mS m-1. A theoretical model is developed to provide a good description of the dependence of the observed translational motion, termed travelling-wave dielectrophoresis (TWD), on the dielectric properties of the particle and suspending medium, on the size of the particle, and on the magnitude and frequency of the applied field. Unlike conventional dielectrophoresis, the TWD effect is found to be related to the imaginary, rather than to the real, component of the induced dipole moment. Dielectrophoresis and electrorotation measurements were made to provide a further understanding of the observed effects and to support the theoretical model.