Positioning and levitation media for the separation of biological cells

Highly polarizable liquid media are very advantageous for electric-field mediated manipulation of microparticles, particularly where negative dielectrophoresis is to be used to avoid close contact between particles and electrodes. However, the use of artificially polar media, or of strong electric fields, may be questionable where live biological cells are to be handled. Therefore, a number of solutions of highly polar substances were characterized in terms of their permittivity, conductivity, dielectric dispersion and osmotic effect. The requirements for dielectrophoretic levitation and the generalized electromanipulation of biological cells and other microparticles are considered. Examples of the positioning and separation of biological cells using some of these aqueous media are given. The cell separations are demonstrated at both the micro and macro scales, the latter using the recently developed technique of lev-vection. Finally, growth and division of electric-field-isolated yeast cells during long-term exposure to the electric fields necessary for this type of separation is reported.