Hydrophoresis for particle and cell separation

Abstract

This thesis presents ‘hydrophoresis’, a novel flow-assisted separation principle for size separation of microparticles and cells. Hydrophoresis refers to the movement of suspended particles under the influence of a microstructure-induced pressure field. Particles subjected to lateral pressure gradients or flows induced by anisotropic microfluidic obstacles dynamically move from the one sidewall to the other sidewall without any active component. Therefore, hydrophoresis exhibits both advantages of field-based and flow-assisted methods that are dynamic particle manipulation and biocompatibility, respectively. To demonstrate the hydrophoretic self-ordering of particles, I have designed and fabricated microfluidic obstacles slanted with respect to a fluid flow in a polymer device made of poly(dimethylsilosane). Experiments were performed with micron, submicron beads, and DNA molecules to verify the strong nature of hydrophoresis such as dynamic particle manipulation and biocompatibility. Micron-sized particles ranged from 10 to 15 μm were discriminated with less than 6\% resolution. DNA molecules of 49 and 115 kb were separated for 0.12 s over the channel length of 5 mm wtih the corresponding separation throughput of 1.7 × $10^6$ molecules/s. For exact characterization of the hydrophoresis, I conducted three-dimensional (3D) measurement of particle positions in a hydrophoretic microchannel by using a mirror-embedded microchannel. The mirror ideally at 45 degrees reflects the side view of the channel and enables obtaining 3D positional information from two different orthogonal-axis images. With this method, I clearly revealed that hydrophoresis is governed by convective vortices and steric hindrance. I also observed that the hydrophoresis enables 3D particle focusing without sheath flows and an accurate flow-rate control. I next developed a new class of a hydrophoretic device composed of slanted obstacles and filtration obstacles for effective separation of ...