Electrokinetic Techniques for Enhancing the Mixing Effect and Manipulating Biological Particles in Microfluidics

The objective of this research is to study the enhancement of the mixing effect and the manipulation of suspended biological particles in microfluidic systems using electrokinetic techniques. The research can be divided as two main parts: the first part involves analyzing methods to enhance the mixing effect in microchannels via transverse electroosmotic flow, and the second part involves investigating the dielectrophoresis (DEP) technique to manipulate and separate bioparticles. In the first part, a DC electroosmotic micromixer with parallel or square wave electrodes on the bottom of the channel was designed. The results show that the mixing effect is rapidly enhanced with these electrode designs, and the required mixing length is reduced from several centimeters to millimeters. In addition, the mixing effect is further enhanced by placing electrodes on both top and bottom of the microfluidic device. Six different patterns of combined electrode designs were investigated in order for an optimal design to be achieved. A chaotic micromixer was also created via periodic switching the transverse electroosmotic flow (EOF) when a low frequency electric field was applied on a pair of electrodes placed at the bottom of the channel. The mixing performance was better than the DC electroosmotic mixer and a shorter mixing length was required. In the second part, analytical, numerical, and experimental techniques were investigated to study the dielectrophoretic force. The holding capability of the DEP gate system with a 3D electrode design was investigated. This provided useful information for designing the DEP gate and sorter system. The experimental behavior of bioparticles such as penicillium brevicompactum (PBC), T-cells, and Escherichia coli (E.coli) bacteria in a continuous-mode dielectrophoretic gate system to realize high efficiency separation of different bioparticles and cells was also investigated. Meanwhile, an analytical method to analyze the dielectrophoretic force with an n-phase AC electric field applied on an interdigitated parallel electrode array was presented. A semi-analytical approach to analyze the dielectrophoretic force for both planar electrode systems and a 3D electrode system was also demonstrated. Both of these analytical methods provide accurate calculation for the dielectrophoretic force, which is important for investigating the behavior of bioparticles with DEP