Mechanism And Experimental Research Of Ac Electrokinetic Manipulation Of Microparticles And Microfluids

Microfluidics is a high and new technology with rapid growth of MEMS, which is integrated in a small chip with sample preparation, biochemistry reaction, separation and detection, in order to achieve different biochemistry reaction and the analysis of product. Since this technology has extensive potential in disease detection, medical selection, provisions control, environment protection and justice identification, many countries pay more attention on this project in order to occupy the leading position.Manipulation of particles and fluids is central in the microfluidics. Although tranditional technology such as mechanics, ultrasound, and electromagnetic et. al. were extensively applied, their weak points of large volume, expensive, low precision and difficult integration limit the miniaturization. However, manipulation of particles and fluids by AC electric fields is popular with microfludics because of the advantage of low power, cheaply-priced, noninvasive, online-detection, and easy for integration. Depending on AC electric fields, many reaserch has been explored, but the work for the detection of membrance capacitance and conductance of different cell circle, manipulation of two-phase flow and AC electrokinetics of metallic microparticles is still unexplored. In addition, this research is significant for the rapid detection of the cell circle, efficiently select of the fluids, electromagnetic direction and medicine transport et. al. Therefore, this thesis focus on above questions.Electrorotation and dielectrophoresis were selected as the basic tools to measure the membrane capacitance and conductance in different cell circle. The peak frequencies of rotation speed and transformational frequencies of positive DEP and negative DEP were derived, which was used to deduce the expressions of the membrane capacitance and conductance. In addition, the quadrupole electrodes were designed and fabricated, the experimental system was set up and the cells in different circle were cultured. The electrorotation and DEP experiments of the cells were carried out and the proceeding was recorded. The membrane capacitance and conductance were calculated based on the experimental results, which were compared in G1 phase and S phase, respectively. More over, the experimental results obtained by DEP and electrorotation were compared. This research provides a method for fancy methos for the rapid detection of the cells in different cell circle.In the exrperimental proceedings for cells and other microparticles, if the sample was driven by the electric field, wen different flows meet in the microchannel, there will be a conductivity gradient at the interface, which can be polarized under the electric field, and then affect the sample transport and biochemistry reaction. In order to analyze the mechanism and main parameters, the two dimensional model of the two phase fluid was founded and the Coulomb force at the interface was deduced, more over, the two and three dimensional simulations were carried out. The effects of the voltage, frequency and conductivity were emphasized and analyzed. Electrodes were designed and fabricated, also the integration was studied. Experiments with different conductivity gradients were carried out and compared with the theoretical analysis. This research will be significant for sample transport, detection of different flows and decrase of the instability.Manipulation of the cells and two-phase flow were all based on the polarization of insulator, while the electrokinetics of the conducting microparticles was rarely mentioned. However, the metallic microparticles have many advantages on electromagnetic direction and medical transport. The electrokinetic characterizations of the gold coated microparticles were proposed. The polystyrene microspheres with the diameter of 10μm, 25μm and 45μm, and the microrods with the diameter of 11μm and 47μmin length were coated a gold layer using chemical method. More over, the gold plating process was simplified.Electrorotation and DEP experiments for the gold coated microparticles were carried out. Theory of electrorotation in the low frequeny range was analyzed, and the expressions of the electrorotation speed and dielectrophoresis were deduced. The theoretical and experimental results were compared.Gold coated microparticles, as the perfect conductor, are more suitable for the connection in the micofluidics and also can achieve automation and integration of the microfluidics. Rapid separation of coated and uncoated microspheres were proposed and the microwires formation in the microfuidic system were carried out. The impedance of the microwire was measured and the formation theory and effects were analyzed. The parallel electrodes with different gaps were used to do the microwire formation experiments, and the impedance of the system with different number of microwires was measured, showing a good conductance. The 1H, 1H, 2H, 2H-perfluorodecnnethiol was used to modify the gold coated pillar surface, and the microwire formation experiments and impedance measurement were carried out. The relusts of coated and uncoated pillars were compared.