Key Technique Study On Microchip Electrophoresis Based On The Optical Detection

As one of important parts of microfluidics, microchip electrophoresis (MCE) technology has gone through several seedtimes during the last 20 years,including fabrication processing and selection of materials, function improvement, as well as system integrated, miniaturized and portable. There are some problems still impeding the development of MCE, such as the complexity of fabrication technique, the operation process complexity of solution introducing into the microchannel. Also the micron-scale optical-path length is so short that the sensitivity of optical detection system is affected seriously. In this paper,based on the basic theory of capillary electro-osmosis flow (EOF), with optical detection methods, all attention are focused on finding solutions to the problems that exist in the MCE technology.EOF,as one of the most important performance indicators of MCE, will influence the precision and veracity of the analysis result. Based on Navier-Stokes equation of the dilute solution under the electric field, neglected the inertial force item in Stokes equations as the theory of low Reynolds number, the EOF mathematics model in MCE micro-channel is set up. Then with finite difference method and multi-step shooting method, the EOF flow shape in the micro-channel on PMMA MCE and the relationship between E and veo are solved respectively. The calculation results indicate that the EOF flow shape in the micro-channel is flat plug-like, and the E ? veo curve is kept the lineariy relation,μeo=2.3×1 0-4cm2/Vs. Current-monitoring method for measuring the EOF rate is adopted. The buffer is borax. The electroosmosis mobility isμeo=3.02×10-4cm2/Vs. The microchannel surface component and valent-state are analysed with XPS spectrum, the results show that the unsaturated bond are existing on the PMMA surface with the milling process, leading to increase the surface charge density, then resulting in a greater intensity of electro-osmotic. According to EOF basic theory,MCE structure design is carried out, at the same time, the study for the fabrication process and the electophoresis experimental is followed along. With CFDRC software, the configuration and geometry parameter of the MCE micro-channel, also the strategy of electric field apllied, are simulated and optimized designing. The optimization parameter of the microchannel width is 50μm, and the electric field strength E is 200V/cm~ 250V/cm.The fabrication techniques about the PDMS and PMMA material are described detailed in this paper. The technique that fabricated the PDMS device with twice mold is presented firstly.With this method the PDMS devices could be released from the PMMA mold easily and perfectly. Then an irreversible bonding process of PDMS chip with ammonia immersion method is developed. These two methods completely solved the fabrication problems of PDMS chip.The ultra-precision computer numerical control (CNC) milling manufacture method is presented in fabrication the PMMA substrate MCE with an ultra-precision CNC milling. As for the PMMA materials chip fabrication, this method is easier to realize the purpose of processing that is forming. A PMMA substrate plane valveless micro-pump driven by the PZT piezoelectric thick film is designed and fabricated with this method too. Then the chip's function and practicability could be increased. The maxium flow rate is 350μl/min, and could complete rinsing microchannel up to 487 times in 1 min. The function of solution introducing, rinsing and sample injection could be completed. Especially, the fabrication process of the PMMA micropump is compatibile with MCE chip's. Integrated design and processing mode improve the availability of the chip.With the TW30SX photodiode as the photo-electric converter device, a UV detection system is set up. With this detection system, 10-11A magnitude of photocurrent can be detected. The total delay time is between 150 ~ 250ms, the output noise is±5mV, the weight of the whole detect system is about 2kg, and the volume is 280×200×150mm3. The absorption rate of single-layer PMMA chip is 0.035at UV light source with the system, while attenuation of the light strength is 16.87% with the bonding PMMA chip.The whole system electrophoresis experiment are developed with indirect UV detection methods. The inorganic anions(Cl-, SO42-)is used as the separation ions. The background buffer solution is 10mmol/L Na2CrO4+0.5mmol/LCTAB, which electroosmotic test results show that the direction of EOF flow is from the cathode to the anode, reversal with the borax buffer. And the mobility of this buffer isμeo=9.15×10-4cm2/Vs. This condition is suitable for the test demand of inorganic anion electrophoresis experimentFinally, with the electromigration sample injection mode in a single micro- channel MCE chip, inorganic anion Cl-and SO42- electrophoresis peak are detected with indirect UV detection method. The single-peak repeatability results are better, also the mixed two ions could achieve the baseline separation, the detection limit is 10-9mol. The performance and stability are better during the experiment of PMMA MCE with the portable detection system. All these work lay a stable foundation for the PMMA MCE further application in the UV absorbance detection.