Dielectrophoretic separation with a floating-electrode array embedded in microfabricated fluidic networks

Abstract

In this study, we proposed a high-throughput separation strategy of the binary colloid mixture by dielectrophoresis (DEP) induced around large-scale bipolar electrode arrays embedded in microfabricated fluidic networks via a thorough numerical investigation. The usage of a floating electrode (FE) eliminates the need of external Ohmic connection to individual array units, therefore potentially steering the faddish design of new microdevice structures. Diffuse charge dynamics within the induced double layer at opposite ends of every FE permit a sinusoidal electric field to penetrate throughout the whole device, as long as the imposed field frequency is beyond the reciprocal resistor-capacitor time constant at the electrode/electrolyte interface. In this special device configuration, FEs interconnect multiple microchannels arranged in parallel. Pockets embedded on the sidewalls of fluidic channels help create strong field gradients at the tip of FEs and sharp pocket/channel junctions, improving the trapping performance of incoming bioparticles subjected to positive-DEP (pDEP) force, while latex beads experiencing negative-DEP (nDEP) stress are electrically squeezed to the midchannel and finally exit as a series of co-flowing thin streams with unequal translatory velocity. Taking the synergy of DEP force, induced-charge electro-osmosis, alternating-current electrothermal streaming, pressure-driven flow, and buoyancy effect into consideration, a numerical model is established to account for motion trajectories of micro-entities in full-scale three-dimensional space using the Lagrange particle track algorithm, as well as testing the feasibility of the device design in separation of the binary mixture containing yeast cells and polystyrene beads. Applying suitable voltage parameters of frequency O(1) MHz and electric field strength O(10) V/mm, highly efficient DEP separation is theoretically achievable under inlet flow velocity on the order of O(1) mm/s, where most of incoming yeasts are captured by pDEP within these five parallel branching channels, while polystyrene spheres are repelled by nDEP away from the FE array to form slim beams co-flowing into the outlet according to the calculation results. The microfluidic separation device exploiting the FE array offers great potential to build up scalable electrokinetic platforms for high-throughput on-chip sample treatment.