Separation of microparticles and biological cells inside an evaporating droplet using dielectrophoresis

Microparticles or biological cells mixed in water were separated using the combination of an electrical force due to dielectrophoresis and a mechanical one generated in an evaporating droplet. Micropatterned electrodes of Au were fabricated on the silicon dioxide layer and were used to generate dielectrophoresis. Polystyrene particles, red blood cells. and E. coli were used as separating objects. Microparticles and biological cells were separated by adjusting the amplitude and frequency of the applied voltage. Although the mechanical force was enough to transport the particles to the boundary of the droplet, nevertheless, it could not detach the particles trapped at the electrode. Based on this work, the microparticles and biological cells can be separated, controlled, and sensed without using a liquid pumping unit.