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A passive mechanical method for the filtration of particles in electrowetting on dielectric (EWOD) devices is presented. Analytical and experimental results show that droplets actuated by EWOD cannot pass physical obstructions unaided at the scales considered here. However, it was possible to pull droplets past the same obstructions using a second droplet. The two droplets approach the obstruction from opposite sides and merge within the pore of the obstruction. The interface on the enabling side of the amalgamated droplet is then actuated to pull fluid through the obstruction. This technique was successful for pore sizes between half and two orders of magnitude below the confined droplet height. This wide range of viable pore sizes will allow for the filtration of particles by size in EWOD devices. It can also be used to filter large particles traditionally used in microfluidic immunoassays or allow for the use of smaller particles to increase sensitivity. Success at pore sizes as small as 2 μm also suggests that filtration of animal cells in EWOD devices is possible. The proposed process is performed without the use of surfactants, which may make it more attractive for applications using biological material.
Date of Publication: Aug. 2011