Carnegie Mellon University
Department of Chemical Engineering
Department of Biomedical Engineering
Center for Complex Fluids Engineering
Center for Environmental Implications of Nanotechnology
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Electrokinetic Particle Sorting and Mixing Technologies

We have developed techniques based on a coupling of dielectrophoresis (DEP) and electrohydrodynamic flows to manipulate colloidal particles and biological cells using micropatterned electrodes.  Particles and cells migrate to either high field or low field traps, according to their induced dipole strengths.  This offers the opportunity to separate particle mixtures according to differences in polarizability.  Whereas DEP separations are typically operated at MHz frequencies, operating at ~ 10 Hz to 1 kHz, where AC electroosmotic flows are established along the edges of the microelectrode features, affords some advantages.  The simultaneous action of DEP and AC electroosmotic drag forces on particles provides a finer level of discrimination to laterally separate particles, making it possible to separate mixtures that are not well separated by DEP (high frequency operation) methods alone. The effect of AC electroosmotic flow on DEP separations is easily visualized for the separation of low dielectric colloids from yeast cells in suspension.

electric field cell separation

Lateral separation of polystyrene colloids and yeast cells.  Low frequency (60 Hz) operation shown at left aligns yeast cells along the microelectrode strip centers, with polystyrene aligned along the strip edges. This placement is dictated by the DEP/AC electroosmotic coupling.  Operation at high frequencies (1 MHz) shown at right instead aligns yeast in the high field traps along the edges and polystyrene in the low field traps in the strip centers and the centers of the insulating glass regions between strips.  This placement is dictated by DEP alone.  We have used this technique to separate mixtures of cells and also to pattern vesicles.  See Zhou et al. J. Colloid Interface Sci. 285, 179-191 (2005). 

Representative Publications

H. Zhou, L.R. White and R.D. Tilton, “Lateral separation of colloids or cells by dielectrophoresis augmented by AC electroosmosis,” Journal of Colloid and Interface Science 285, 179-191 (2005). DOI: 10.1016/j.jcis.2004.11.040

H. Zhou, L.R. White, R.D. Tilton, “Microphase separation during binary electrophoretic deposition of particles with dissimilar polarizabilities,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, 277, 119-130 (2006). DOI: 10.1016/j.colsurfa.2005.11.025

M.A. Matos, L.R. White, R.D. Tilton, “Electroosmotically enhanced mass transfer through polyacrylamide gels,” Journal of Colloid and Interface Science, 300, 429-436 (2006). DOI: 10.1016/j.jcis.2006.03.036

M. Matos, L.R. White, R.D. Tilton, "Enhanced mixing in polyacrylamide gels containing embedded silica nanoparticles as internal electroosmotic pumps,” Colloids and Surfaces B: Biointerfaces 61, 262-269 (2008). DOI: 10.1016/j.colsurfb.2007.08.013

J.K. Lim, H. Zhou, R.D. Tilton, “Liposome Rupture and Contents Release over Coplanar Microelectrode Arrays,” Journal of Colloid and Interface Science 332, 113-121 (2009). DOI: 10.1016/j.jcis.2008.12.035