Manipulation and patterning of colloids and biological cells near electrode surfaces

The goal of this thesis research is to develop the capability to organize colloidal particles and biological cells based on electrohydrodynamic and/or dielectrophoretic techniques in a microelectromechanical system (MEMS). Particular emphasis is placed on the ability to separate binary mixtures of particles or cells based on differences in their dielectric properties. It is envisioned that these concepts can be integrated with life science and biomedical technologies (bioMEMS) to develop novel technologies such as biosensors based on addressable cell arrays, microfluidic bioreactors, and general purpose cell separation devices that do not require molecular affinity probes.; This research focuses mainly on the assembly behaviors of carboxylated polystyrene (PS) colloidal particles, as a model system for non-biological colloids, and yeast cells as a model system for biological colloids. Red blood cells are briefly examined in binary mixtures with yeast, in order to demonstrate the ability to separate mixtures of cells based on their dielectric properties. Assembly is conducted adjacent to an electrolyte/electrode interface formed by transparent indium tin oxide (ITO)-coated glass substrates in the presence of 0.1 mM NaHCO3. All electric fields are alternating current (AC). Both uniform electric fields and non-uniform electric fields are considered, the latter generated by a micropatterned ITO electrode array.; In uniform AC fields, PS colloids assemble by a well-known process that has been termed electrophoretic deposition (EPD). Microscopic image analysis shows that the microphase structure within the PS assemblies is dependent on the field frequency. At low frequency, 5 Hz, the microphase structure of the PS assemblies is also dependent on the PS size and zeta-potential. For a binary mixture of PS colloids and yeast cells, a two-dimensional, microphase separation occurs when applying 5 Hz, 10 V/cm AC electric fields, forming self-organized core-shell clusters with predominantly yeast cores surrounded by shells of polystyrene (PS) particles. Systematic experimental studies and theoretical analysis show that the PS particle size and zeta-potential exert only a secondary effect on the core-shell microphase structure.; By combining both experimental investigation and theoretical analysis, this thesis research work demonstrates that the coupling of electrohydrodynamic flow and dielectrophoretic forces can be effective for differentially manipulating different types of particles based on their dielectric properties. The thesis concludes with suggestions for how this concept can be exploited for the development of new strategies for colloidal patterning, separation, manipulation, microfluidics and bioMEMS technologies. (Abstract shortened by UMI.)...