A dielectrophoretic-gravity driven particle focusing technique for digital microfluidic systems

In the present study, a particle focusing technique functioning based on the cumulative effects of gravity and negative dielectrophoresis (nDEP) is developed for digital microfluidic (DMF) systems. This technique works using the conventional electrodes used for droplet manipulation without a need for geometrical modification. Particle manipulation is performed by applying an AC voltage to the electrode above which there is the droplet containing the non-buoyant particles. The particles sediment due to the difference between the gravitational and the vertical component of the nDEP forces, while the horizontal component of the nDEP force concentrates them on the center of the electrode. Therefore, the magnitude of the voltage must be kept within an effective range to have simultaneous effects of sedimentation (dominated by gravity) and concentration (due to the horizontal component of the nDEP force). The physics of the phenomenon is explained using simulation. The effects of the magnitude of the applied voltage, the particle size and density, and the electrode size on the focusing behavior of the particles are studied. Finally, a potential application of the present technique is illustrated for particle concentration in DMF. (C) 2015 AIP Publishing LLC.