Electric and Microfluidic Manipulation of Molecules and Particles in Microfabricated Devices.

Abstract

Microfabrication technology has enabled traditional chemical and biological research to be performed at the micrometer scale, but the control of particles suspended in fluids and the fluids themselves remain a significant challenge. This dissertation is aimed at developing simple and versatile control systems for fluids and small entities (e.g., particles and molecules) in fluids. Accordingly, three methods have been explored using electric and fluidic micromanipulation, as well as physical deposition. First, dielectrophoretic DNA positioning and elongation in a microchannel have been examined with modified surface chemistry and electrode conditions. Less hydrophilic surfaces provided more controllable stretching, presumably due to the decreased non-specific adsorption of DNA on these surfaces compared to their more hydrophilic counterparts. Smoothed electrode edges allowed more controlled stretching, and, moreover, thin electrodes (50 nm) provided dense electric field and gave ~90% success rate of DNA stretching. Second, a microstencil method has been developed to pattern thermally and chemically sensitive materials. The microstencil has a bi-layer structure comprised of two polymeric films (i.e., parylene and SU8). The parylene layer enables the microstencil to be mechanically peeled from hydrophilic substrates and SU8 provides height to control the amount of material deposited. The amount is also controlled externally by performing multiple spin or dip coating processes. As an initial demonstration of the method, a wide range of chemically and thermally labile materials has been patterned: wax, cells, and proteins. Third, a continuous synthesis system for anisotropic microparticles with different shapes and sequences has been developed. The anisotropic particles are configured by exploiting a combination of geometrical confinement and microfluidics to pack particles into a narrow, terminal channel, and the packed particles are then bonded by thermal fusing. The width and length of the channels reproducibly specify the configuration of the anisotropic particles that will be produced. Complex sequences are obtained by coupling the sequential actuation of metering lines with the input flow of different particles. By using the process, linear and triangular homogeneous (A) and heterogeneous (A-B and A-B-A) particle chains have been synthesized.