Particle Electrophoresis and Magnetophoresis in Microchannels

In current pharmaceutical and biotechnology industries with clinical applications, an increased demand for flow control and cell manipulation on the micrometer scale has emerged. Electrokinetic, magnetic and many other physics fields have been exploited to meet this demand. However, due to the requirement for sophisticated micro-structures and the interference of the increasing significance of many `trivial\u27 physics properties (surface potential, permittivity, etc.) at the smaller scale, most applications encounter poor maneuverability and high operation/fabrication complexity issues. Very few attempts have been made to bypass these requirements while maintaining the same control and efficiency. This thesis research investigates the fundamental behaviors in microfluidic particle transportation. Then, with a thorough comprehension of the governing parameters and key effects, practical applications can be designed and developed to resolve the aforementioned microfluidic technique issues of electrophoresis and magnetophoresis. This thesis consists of two main parts. In the first section, the basic manipulation principle and subsequent applications in particle electrophoresis are discussed. Based on an observed wall-induced particle deflection in a straight microchannel, this thesis developed a method to three-dimensionally focus particle stream to the microchannel center. This application only relied on the particle confinement with respect to the microchannel; no particular external forces had to be exerted since this phenomenon was self-developing along with the traveling in the lengthwise direction. The second half of this work shifted the focus to particle magnetophoresis in a straight microchannel. An analytical model was built that solved the coupled magnetic and flow field, confirmed the experimental observations and enabled predictions for other plausible applications. Following that, this work utilized this negative magnetophoretic deflection to implement a diamagnetic particle focusing in a T-shaped microchannel. Particle ferrofluid flow and axillary sheath flow moved within each half of the microchannel and, the magnetophoretic deflection took effect inside the ferrofluid half where the particles were focused on the interface between the two halves. This arrangement required only one magnet with the help of the sheath flow to restrain the effective magnetophoretic deflection, which tremendously reduced the fabrication complexity and extended the channel-magnet distance to a smaller magnitude, therefore enhanced the throughput. Lastly, the same T-shaped microchannel was proved to perform high efficient particle separation. In addition to the negative magnetophoresis induced deflection for the diamagnetic particle was applied, the `attraction\u27 for the magnetic particle was present at the same time due to the opposite reaction: positive magnetophoresis. Initially mixed diamagnetic and magnetic particle sample were injected into the microchannel and, the opposite responses to the magnetic field formed a continuous separation of these two types at the end of the microchannel. Compared to the batch-mode MACS (magnetic cell sorter), this method undoubtedly made an improvement in both the throughput and operative difficulties