Focusing and separation of particles and cells activated by passive microfluidic systems

Microfluidics is a field of science and engineering that deals with the manipulation and control of fluids, usually in small volumes ranging from nanoliters to microliters, within micro-scale devices. Microfluidic focusing and separation are techniques used in microfluidics to control the movement and separation of particles or cells within a microfluidic device. In this thesis, passive microfluidic systems using hydrodynamic forces inside a microchannel are developed by the author for the focusing and separation of synthetic particles and cells. Hydrophoretic techniques taking advantages of the glass microstructures engraved by femtosecond pulse laser (fs laser) is achieved for aligning polystyrene beads and live cells in chapter 2 and 3. The focusing performance proves to be influenced by channel length, particle diameter, particle type, groove angle and middle open space. It is the first time that fs laser-engraved microstructures are applied for hydrophoretic focusing of particles in microfluidics. The investigation is expected to be integrated with the particle separation approach for future use. Then, a viscoelastic microfluidic platform is established for the separation of Escherichia coli (E. coli) either by shape or size in chapter 4 and 5. After antibiotic treatment, a portion of E. coli become sphere-like. The sphere-shaped E. coli are isolated from the cell mixtures with the microfluidic device, demonstrating shape-based separation of a single species of bioparticles smaller than 4 μm for the first time in microfluidics. Also, this microchip shows the capability for the separation of E. coli singlets and clusters, providing the new approach for isolating the cell clusters. By collecting the E. coli with uniformed shapes or sizes, the constructed platform hopes to facilitate the investigation of biochemical and molecular factors governing antibiotic resistance or biofilm development. Further, in chapter 6 size-based separation of particles is realized by inertial microfluidics, where symmetrical sheath flows are used innovatively. Separation of platelets from whole blood is shown using the microfluidic system. This exploration provides a novel perspective for particle separation. With the purpose of establishing passive microfluidic systems for the focusing separation of particles and cells, the thesis sequentially develops hydrophoretic, viscoelastic and inertial microfluidic approaches. The passive microfluidic platforms are hoped to be used by the researchers from the fields like microfluidics, laser fabrication, physics, biology and biomedicine for promoting the science development.