(A) continuous size-dependent particle separator using a negative dielectrophoretic virtual pillar array

Abstract

This study presents a continuous size-dependent particle separator using a negative dielectrophoretic (DEP) virtual pillar array. Two major problems in previous micromechanical size-dependent particle separators were particle clogging in the mechanical sieving structures and a fixed range for the separable particle sizes. The proposed particle separator uses a virtual pillar array induced by negative DEP force in place of a mechanical pillar array, thus eliminating the clogging problems. Repulsive negative DEP force is induced by applying voltage to a spot electrode on a substrate. It is possible to adjust the size of separable particles, as the size of the virtual pillars is a function of a particle diameter, applied voltage, and flow rate. The separation purity, the effective barrier size, and the separation position of polystyrene (PS) beads with diameters of 5.7 ± 0.28 μm-, 8.0 ± 0.80 μm, 10.5 ± 0.75 μm, and 11.9 ± 0.12 μm were measured under two types of the applied voltage (500 kHz sinusoidal waves of 10 $V_{rms}$ and 8 $V_{rms}$) and the flow rates (0.40 μl $min^{-1}$ and 0.30 μl $min^{-1}$) to characterize the size-dependency of particle separation. The medium conductivity was 200 mS $m^{-1}$ which kept DEP characteristics of the PS beads constant. The 5.7 μm-, 8.0 μm-, 10.5 μm-, and 11.9 μm-diameter PS beads were separated at separation purity of 95%, 92%, 50%, and 63%, respectively, at an applied voltage of 500 kHz, 10 $V_{rms}$ (root mean square voltage) sinusoidal wave and a flow rate of 0.40 μl $min^{-1}$. The 10.5 μm- and 11.9 μm-diameter PS beads had relatively low separation purity of 50% and 63%, respectively. However, at an applied voltage of 8 $V_{rms}$ and a flow rate of 0.40 μl $min^{-1}$, 11.9 μm-diameter PS beads were separated with separation purity that exceeded 99%. Additionally, 5.7 μm-diameter PS beads were separated with separation purity that exceeded 99%, at an applied voltage of 500 kHz, $V_{rms}$ and a flow rate of 0.30 μl $mi...