Optimization And Application Of Differential Streaming Potential Measurement Over Micro-Channels And Fabrication Of A Miniaturized Fluorescence Detector For Micro-chip Electrophoresis

In the21st century, we are more concerned about health-related biochemical parameters, food safety, and environmental status. It is of great significance to develop rapid, accurate analytical methods and economical, portable and easy-to-use point of care (POC) devices that can be used for disease diagnosis, quantitative assessment and decision-making of public safety events, such as burst of infectious diseases or unexpected environmental accidents. As a promising way toward miniaturization, microfluidics has attracted much attention because of its unique advantages. Because surface properties of microchannels have direct impact on its applications in almost all aspects, it is urgently needed to establish new methods for microchannel surface characterization.Therefore, this dissertation focused on developing fast and simple surface characterizing methods for microchannels and building an economical fluorescence detector for chip electrophoresis. Originalities include:1.A novel difference streaming potential (SP) measurement method was developed to characterize the surface charge of microchannels. The method has the advantages of fast and simple operation and good reproducibility.2. Factors that might contribute to the variation of SP measurements were systematically investigated and the way to ensure the reproducibility was proposed.3. Differential SP measurement was used as a new biosensor, and label-free detection of thrombin was tested.4. An economical fluorescence detector was built with a low-cost avalanche photodiode working in current mode as the photon receptor and a blue LED lamp as the light source.The dissertation consists of five chapters.Chapter Ⅰ:Techniques that can be used for surface characterization including contact angle measurement, atomic force microscopy, attenuated total reflection fourier transform infrared spectroscopy, electroosmotic flow measurement and streaming potential measurement were reviewed. A short introduction of microfluidics and its application was also presented.Chapter Ⅱ:A novel difference streaming potential technique was extended for rapid and accurate characterization of microfluidic channels. The technique exhibited advantages of simple instrumentation and operation, fast measurement, five parallel determinations could be completed within1minute, good reproducibility, and the relative standard deviation (RSD) for multiple measurements with the same capillary was normally less than1%.Chapter Ⅲ:To ensure accurate SP measurement, a micro conductivity probe and a micro pressure sensor was incorporated into the system and a reference channel was also implemented. The results showed that on-line conductivity correction could eliminate the influence caused by variation of solution composition, and pressure monitoring could help to compensate the variation of presusrre drift and help the operator find improper experimental conditions. With the reference channel, variation of SP caused by conductivity, pressure and other unknown factors could be successfully corrected, and RSD of inter-day measurements could be decreased from15.2%to1.2%.Chapter Ⅳ:Condition of capillary modification was optimized with the aid of the difference streaming potential technique. The interaction of thrombin and thrombin aptamer was investigated through immobilizing thrombin on the modified capillary wall. A SP-based label-free and immune biosensor was proposed. The SP responses and thrombin concentrations were found linear in a concentration range of500nmol/L～10μmol/L, and the equation was:y=2.514x-1.880(Rz=0.9800).Chapter Ⅴ:An economical fluorescence detector was developed with an LED as exciting source and a low cost avalanche photodiode module (1cAPD) as a photon sensor. The performance of the detector was evaluated by electrophoretic separation of FITC labeled amino acids either in capillary or micro-chip format. A limit of detection of0.2nmol/L for sodium fluorescein was attained, which is among the lowest ever achieved with an LED as an excitation source. Linear range was0.01-10μmol/L. The detector is suitable for high sensitive detection of capillary and chip electrophoresis.