Microparticle concentration and separation by traveling-wave dielectrophoresis (twDEP) for digital microfluidics

This paper describes highly efficient in-droplet particle concentration and separation where particles are concentrated and separated into droplets by traveling-wave dielectrophoresis (DEP) and subsequent electrowetting-on-dielectric droplet splitting. A successful concentration for 5-mu m aldehyde sulfate (AS) latex particles was experimentally achieved using microfabricated devices, showing that 98% of the total particles were concentrated into a split daughter droplet. In addition, in-droplet particle separation was successfully achieved using the following two different cases of particle mixtures: case 4) a mixture of 5-mu m AS latex beads and 8-mu m glass beads; and case 2) a mixture of ground pine (GP) spores and 8-mu m glass beads. In case 1), 97% of the total AS beads were separated into one split droplet and 77% of the total glass beads into the other split droplet. In case 2), over 92% of the GP spores were separated into a split daughter droplet, whereas 86% of the glass beads were separated into the other split daughter droplet. In all these concentration and separation experiments, the applied frequency and the conductivity medium are key parameters influencing the concentration and separation performance, which have been optimally determined by measuring the DEP and electrorotation spectra of the used particles prior to the concentration and separation experiments. This integrated in-droplet separation and concentration method may provide an additional functionality to digital microfluidics.