(394d) Micron-Scale Ion Concentration Gradients in Nonuniform AC Electric Fields

Minerick, A. R., Michigan Technological University

Micron-scale Ion Concentration Gradients in Nonuniform AC Electric Fields


Department of Chemical Engineering

Michigan Technological University, Houghton, MI 49931

Erythrocytes were observed to first swell slightly and then shrink substantially over time in phosphate buffer saline in a two dimensional nonuniform AC dielectrophoretic field. We hypothesized that this cell behavior was due to changing osmotic pressure between the cell and the local medium as propagation of an ion concentration gradient occurs in the electric field area. Cells are known to respond rapidly to the tonicity of the surrounding media; isotonic media yields an erythrocyte typical biconcave shape while hypotonic will cause erythrocytes to swell and hypertonic cause cells to shrink. Experimental results were examined to describe the cell shrinkage behavior in initially isotonic buffer solution under nonuniform AC DEP field. Results have shown that cell shrinkage can be observed from 180 seconds close to the higher field density region and will expand to the lower field density region under high frequency (1 MHz) AC field. Also, cell shrinkage starting time will change with the change of applied signal frequency and peak-to-peak potential. Ion behaviors were examined with COMSOL ‘Transport of Dilute Species’ physics to simulate diffusive, convective and electromigration transport under experimental conditions. Results have shown that high ion concentration increased in the regions adjacent to the electrode over 100 cycles of the AC field. These results have important implications in the field. Research in this field has, until now, assumed polarization of dielectrics in dielectrictrophoretic fields occurs in relatively constant medium conditions. The Debye layer comprises tens to hundreds of nanometers from the dielectric particle surface or electrode particle surface; ion behaviors in this layer have been studied. This work elucidate the formation and transportation of waves of ions tens to hundred of microns from the electrode surfaces in non-uniform AC electric fields and corresponding experimental results suggest complex interaction between the dynamic ion distribution in the medium and the particle’s induced dipole response.