Precisely sized separation of multiple particles based on the dielectrophoresis gradient in the z-direction

We present a new 3D dielectrophoresis-field-flow fraction (DEP-FFF) concept to achieve precise separation of multiple particles by using AC DEP force gradient in the z-direction. The interlaced electrode array was placed at the upstream of the microchannel, which not only focused the particles into a single particle stream to be at the same starting position for further separation, but also increased the spacing between each particle by the retard effect to reduce particle–particle aggregation. An inclined electrode was also designed in back of the focusing component to continuously and precisely separate different sizes of microparticles. Different magnitudes of DEP force are induced at different positions in the z-direction of the DEP gate, which causes different penetration times and positions of particles along the inclined DEP gate. 2, 3, 4, and 6 μm polystyrene beads were precisely sized fractionation to be four particle streams based on their different threshold DEP velocities that were induced by the field gradient in the z-direction when a voltage of 6.5 Vp–p was applied at a flow rate of 0.6 μl/min. Finally, Candida albicans were also sized separated to be three populations for demonstrating the feasibility of this platform in biological applications. The results showed that a high resolution sized fractionation (only 25% size difference) of multiple particles can be achieved in this DEP-based microfluidic device by applying a single AC electrical signal.