From electrophoresis to dielectrophoresis: designing, fabricating, and evaluating an electroformed ratchet type microfluidic dielectrophoresis device Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6m311t61r

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  • Dielectrophoresis (DEP) is a separation method in which a non-uniform electric field is used to induce a dipole moment in a suspended particle. If the polarization of the particle is greater than that of the suspending medium, the particle will move towards the region of higher field strength (positive DEP); while if the particle is polarized less than the suspending medium, the particle will be moved towards the low potential area (negative DEP). In recent years DEP has been gaining popularity through the construction of microscale devices, and this is due largely to the decrease in electrode spacing which allows for higher effective field strengths. Presented is the design, fabrication, and evaluation of a novel dielectrophoretic based ratchet device. The electrodes required to produce the asymmetrical field were constructed of electroformed nickel features grown on the surface of a resist patterned seedlayer coated glass slide, and this is the first time electroforming has been used to produce electrodes in the field of DEP. The electrodes were then made stand alone features located on the glass slide by wet etch removal of the unplated portions of the seedlayers located on the surface of the glass substrate. The fluidic component of this device was constructed using replica molding of poly(dimethylsiloxane), which contained a fluidic reservoir located over the ratchet electrode features. Particle selection was conducted using an a priori approach for particles of known dielectric properties. The frequency responses of perspective test particles to an asymmetrical electric field were determined through calculation of the real component of the Clausius-Mossotti factor (Re[K(ω)]). From these calculations, magnetite and polystyrene spheres were selected as test particles. The device was then evaluated using the test particles selected to determine if particle collection occurred in the regions dictated by Re[K(ω)]. Suspensions consisting of single particle types and a mixture were then evaluated, and it was found that the particles collected in the regions specified by the theoretical calculations. These results showed that the device is capable of collecting particles based on the dielectric properties of the magnetite particles and polystyrene spheres.
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