A dielectrophoretic filter for separation and collection of fine particles suspended in liquid

Dielectrophoresis (DEP) is the electrokinetic motion of dielectrically polarized particles in nonuniform electric fields. DEP has found many useful technological applications including separation, levitation and characterization of dielectric particles such as biological cells. In this study, the authors propose a new type of liquid filter, which utilizes dielectrophoretic force (DEP force) to capture fine particles suspended in liquid. The DEP filter consists of an electrode system that is filled up with many dielectric particles. These particles modify the electric field distribution in the electrode system so that strong DEP force is generated on their surfaces. If the DEP force is stronger than drag force exerted by liquid flow in the filter, the suspended particles can be trapped and eliminated from the flowing liquid. The DEP filter can control trapping and releasing process just by changing electrode energizing ac signal and the resultant DEP force. It was experimentally confirmed that the DEP filter could continuously eliminate yeast cells suspended in water. The cell density decreased from 10⁶ cells/mL to 10¹ cells/mL in about an hour. The electrical conductivity of the medium was a crucial parameter that influenced the liquid temperature by Joule heating and DEP force. Further-more, the selective separation of viable and nonviable yeast cells was demonstrated by utilizing viability dependency of the DEP force.