(535c) Application of Capillary Electrophoresis to Predict Crossover Frequency of Polystyrene Particles in Dielectrophoresis

Dielectrophoresis with AC electric fields provides spatial separation of a variety of particles. Depending on the experimental conditions, the particle may respond with positive or negative dielectrophoresis. Under appropriate conditions, this switch from negative to positive dielectrophoresis can be used segregate particles by controlling the frequency. This is easier to accomplish if the permittivity and conductivity of the particles and the aqueous medium suspending the particles are known. The particle conductivity may be determined if zeta potential viscosity, double layer thickness, and the particle radius are known. Capillary electrophoresis instrumentation is useful for measurements of viscosity and electrophoretic mobility of the particles, from which zeta potential is then calculated. Measurements with capillary electrophoresis instrumentation are rapid and sample volumes introduced into the separation capillary range from nano- to femtoliter depending on the separation parameters. The approach is demonstrated with polystyrene particles, which have been subject to different chemical modification. The zeta potential is derived from capillary electrophoresis experiments under different conditions. The DEP behavior of the particles is observed in a frequency range of 100 kHz - 3 MHz using a DEP cell containing fabricated gold quadrupole electrodes. The particles undergo positive DEP and accumulate near the edges of the quadrupole electrodes used in this study. When the force is negative, the particles undergo negative DEP and collect in the center of the four electrode array. The particle surface conductivities derived from capillary electrophoresis separations differ from those derived from dielectrophoresis experiments by ≤ 0.003 Sm-1 and serve as a guide to effectively select the suspending medium to generate a crossover frequency ~ 0.5 MHz.