| Microchip electrophoresis is an important area of microfluidics that has been actively studied and widely used in analysis of various samples due to its advantages including rapid analysis speed, high separation efficiency and easy for miniaturization. However, because of the complicated procedure for microchip fabrication and other related factors, its application in the routine analysis is still rather limited. To reduce the costs and improve the application of microfluidic systems in real analysis, much effort have been put to use polymers as substrates of micro-chips. Cyclic olefin copolymer (COC), which is a newly commercialized polymer, has been proved to be promising material of micro-chips due to its unique optical and mechanical properties. However, the surface of COC is hydrophobic and lacks proper functional groups, which may cause non-specific adsorption of biomacromolecules and thus restrict the further application of COC microchips in the fields of bioanalysis. Therefore, it is essential to develop efficient methods to modify COC and evaluate their effects on the performance of COC-microchip electrophoresis. The establishment of practical analytical methods based COC microchip is also of great importance. The novelty of the present work mainly focuses on following aspects:A computer programmable high voltage power supply was constructed using cheap and easily available materials and electronic parts. The voltage outputs was stable and could be rapidly switched and linearly programmed for either increase or decrease. The design of this power supply provided an essential support for the high voltage control of microchip electrophoresis in the following work.By dynamic modification of COC microchannels, several important alkaloids and amino acids have been separated and analyzed through microchip electrophoresis. The proposed methods are rapid, sensitive, highly efficient and easy to perform.The microchannels of COC chips have been grafted with different acrylic monomers by ultraviolet initiated polymerization to introduce diverse functional groups and surface charges. The performance of the modified microchips has been evaluated by electrophoresis. This modification method has advantages of simple operation, short reaction time and mild reaction conditions.There are five chapters in the dissertation:Chapter one:The review. We have summarized the history of microfluidics, the preparation of microchips, the modification of the micro-chips and the applications of microfluidics in various analyses. Based on this background, the main topic of our research and its necessity have been introduced.Chapter two:Construction of a computer programmable high voltage power supply utilizing cheap and easily available materials and electronic parts has been described. The performance of the power supply was systematically evaluated. The results indicated that its output voltage was linearly proportional to the control voltage. the response was fast and the switch of the voltages was rapid. Linear increase or decrease of the output voltages could be realized by proper computer programming. The power was used in capillary electrophoresis to evaluate its applicability and the results demonstrated that the power supply was competent for the measurement of electroosmotic flow through current monitoring and the separation of the mixtures of two real samples.Chapter three:Two important alkaloids, ephedrine and pseudoephedrine, were separated and analyzed by COC microchip electrophoresis using dynamic modification with hydroxypropyl cellulose (HPC). With laser induced fluorescence (LIF) detection, the optimized conditions for sample separation were screened for influencing factors of dynamic modification and separation. Meanwhile, the conditions for fluorescein isothiocyanate (FITC) derivation were also optimized. Under the selected condition, ephedrine and pseudoephedrine could be separated within140s and the detection limits of0.4nmol/L and1.2nmol/L, respectively, were attained. The method was also successfully analyzed the alkaloids in real samples, suggesting the success of the dynamic modification of COC chips.Chapter four:FITC-derivatized taurine was effectively analyzed through microchip electrophoresis with COC chip modified by HPC dynamically. Under the optimized conditions, the mixture of taurine and five other amino acids was separated within70s, and the detection limit for taurine reached0.5nmol/L, indicating that the assay was rather rapid and sensitive. The method was successfully applied to determine taurine in a series of real samples, which implied that the method had potential in food and medicinal analysis.Chapter five:The microchannel surfaces of COC chips were grafted with six acrylic acids monomers by ultraviolet initiated polymerization. The conditions of grafting such as initiators, monomer concentrations, irradiating time and temperature were studied systemically and the optimized conditions were selected. The modification with monomer2-acrylamide-2-methylpropanesulfonic acid which containing sulfur was used as a model to be characterized by attenuated total reflection infrared spectrometry and X ray photoelectron spectroscopy. The results confirmed the existence of the polymer layers on the channel surfaces. The mixture of four kinds of amino acids were separated well through microchip electrophoresis with microchannel surfaces carrying two different charges, while the migration order of the peaks were opposite, which indirectly demonstrated the successful modification. |
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