Direct Current and Low Frequency Polarization Behavior of Polystyrene Particles in Insulator-Based Dielectrophoretic Devices

Differences in particle polarization behavior can be effectively exploited to achieve desired particle separations with microfluidic electric-field driven techniques, such as dielectrophoresis (DEP).This work studies the dielectrophoretic behavior of polystyrene particles of four different diameters (100-nm, 200-nm, 500-nm and 1-µm) when direct current and low frequency (<1 kHz) electric potentials are applied in insulator-based DEP (iDEP) devices. The Clausius-Mossotti factor, which accounts for the relative polarization of the particles with respect to the suspending medium, indicates whether particles will exhibit positive or negative dielectrophoretic behaviors. The effect of particle size, medium conductivity and frequency in the polarization behavior of the particles was studied both mathematically and experimentally. The results presented here show that positive and negative dielectrophoretic behaviors can be obtained in iDEP devices. Specifically, smaller particles tend to exhibit positive DEP at higher frequencies, while larger particles tend to exhibit negative DEP at lower frequencies. These differences in the polarization behavior of particles is a result of the overall conductivity of the particle, controlled by the relative contributions of the Stern and diffuse layers.