(A) two-dimensional particle focusing channel using the positive dielectrophoresis (pDEP) guided by a dielectric structure between two planar electrodes

Abstract

We present a two-dimensional particle focusing channel using the positive dielectrophoresis (pDEP) guided by a dielectric structure between two planar electrodes. Compared to hydrodynamic and nDEP focusing methods, the present focusing chip achieve the simple and effective 2D particle focusing without additional fluidic ports and top electrodes, thus being suitable for integrated biological analysis systems. When AC voltage is applied to two planar electrodes, the dielectric structure between two planar electrodes induces the maximum electric field at the center of the microchannel. Particles are focused into the center of the microchannel by positive dielectrophoresis (pDEP) as they flow from the single sample injection port. We design the dielectric structure and electrodes to focus particles at the center of the microchannel. The channel is designed as 50 μm wide and 50 μm high. The height of the dielectric structure is 25 μm, half of the channel height, with 10 μm width considering adhesion problem of high aspect ratio structure. The length of the electrodes for focusing is designed as 2 mm to achieve more than 90 % focusing efficiency estimated from the numerical analysis of the particle trajectory. Focusing efficiency is defined by the number of particles in the focusing region (5 μm $\times$ 5 μm) over the number of total particles. Device are fabricated by photolithography and PDMS molding process. In the experimental study, we observed the distribution of focused particles and obtained focusing efficiency using 2 μm-diameter polystyrene (PS) beads for varying applied voltage and flow rate. The position of focused particles is measured as 0.17 ± 1.8 $\mu$m on the x-z plane (top-view) and 3.68 ± 1.9 $\mu$m on the y-z plane (side-view) at 20 μm away from the back end (exit) of the dielectric structure with the sample flow rate of 0.01 μl/min and 15 kHz square wave voltage of $15 V_{p-p}$. At the applied voltage over $15 V_{p-p}$ and the fi...