Preparation,Surface Modification And Their Application Of Low-cost Polymeric Microchips For Electrophoresis In Food Analysis

Microfluidic analysis, which with advantages including less sample/solution consumption, fast analysis speed and easy integration, has been widely applied in food safety assay, environmental pollution monitoring and cell analysis. However, the application of microfluidic techniques in real-world analysis is limited. Expensive glass microchips prepared through complicated fabrication process can be a reason, while polymeric microchips which is normally rather cheap but their application is limited by the hydrophobic surfaces and their non-specific adsorption of biomolecules like proteins. In certain cases, the conventional sample derivatization that takes far more longer time than the microfluidic analysis itself also intimidates the application of microfluidic analysis in the real world. Therefore, exploring novel microchip fabrication and surface modification methods, improving the applicability of microfluidic analysis are still the urgent task of analytical chemistry. This thesis focuses fabrication surface modification and application of polymeric microchips in microchips electrophoresis. Fabrication of polymeric microchips with different materials and that with various microchannels, surface modification protocols and evaluation, optimization of microchip electrophoresis procedures, on-line derivatization and the application of microchip electrophoresis in food safety related analysis were investigated. The novelty of this thesis includes:(1) A facial way toward mass production of long turning and serpentine channel microchips has been proposed, and the prepared microchips were applied in electrophoresis and used as microreactors for complicated chemical reactions.(2) Polyvinyl chloride (PVC) was used to make microchips for electrophoresis with hot embossing, the zwitterionic polymer buffer additive was synthesis by ATRP and applied in separation of protein.(3) Two monomers with different charges was introduced onto the COC surface by UV initiated polymerization modification. The formed zwitterionic layers effective eliminated the nonspecific adsorption of proteins. With the proposed method, it is easy to tailor the pi of the surface through change the ratio of the two monors.(4) The characteristic patterns of aminoacids and their contents of different bands soy sause was easily evaluated by microchip electrophoresis, and the results were verified by the traditional titration method.(5) Double helix channels on microchips were fabricated for online derivatization of aldehyde flavors together with electrophoretic separation. The integrated microchip was applied in determination of aldehydes in chocolate and infant cereal samples.There are six chapters in this thesis:Chapter 1:The materials and processes used to fabricate microfluidic chips> surface modification、sample preparation, microchip electrophoresis system and their detection techniques were shortly reviewed. The necessity of research presented in this thesis was explained.Chapter 2:A modified hot embossing method to fabrication the long serpentine channel microchip has been described. With bonding the glue layer on the glass slide, the copper wire was fixed with precise position. Using this method, fabrication of long serpentine channel microchip is much more easier and it effectively reduce the manual operation uncertainty. The loss of the separation efficiency with different turning radii (4 mm/5 mm/10 mm) was evaluated. The result indicated that the negative effect of tunning was decreased along with the increase of the radius. A 14 cm long microchipwith 10 mm tunning radii was applied for the electrophoresis of fourteen amion acids. Based on this method,51 cm channel microchip was made by steel mould and applied for on chip derivatization of aldehydes.Chapter 3:Hot embossing for fabrication of PVC microchips was attempteded. According to the surface and fluorescence of the substrate, the embossing of substrate and microchannel temperatures were selected at 170 ℃ and 160 ℃. The diameter shrink of the microchannel was within 5 μm when bonding time changed from 5 min to 25 min, which indicatied the bonding time has little effect on diameter of microchannels. After modification by hydroxypropyl cellulose, the contact angles was decreased from 74.5° to 30.2°. The polymer buffer additive was synthesis by ATRP and applied in separation of amion acid and green fluorescent protein.Chapter 4:UV photochemical method to form zwitterionic layers on the surface of microchannels of cyclic olefin copolymer (COC) using two mixed acrylic monomers, 2-acrylamido-2-methyl-l-propanesulfonic (AMPS) and [2-(acryloyloxy) ethyl] trimethyl ammonium chloride (AETAC), were described. With different initial monomer type and ratio, the obtained surface charge can be easily tailored. The modified surfaces were also characterized with contact angle measurement, XPS, ATR-FTIR. The contact angles was decreased from 75°to 33.0-44.3° which indicatied the modified layers of COC are hydrophilic. Through adjusting the ratio of mixed monomers, the pI of the surface can be changed from 3 to 9. The modified layer effectiveness for elimination of nonspecific adsorption of three proteins with different pIs were checked with streaming potential and fluorescent microscopy. The uniformity of the modified surface was proved with microchip electrophoresis. Finally, the microchip was applied in the measurement of whole blood coagulation time.Chapter 5:In this work, an efficient microfluidic electrophoresis separation is proposed for the evaluation of 4 different brands Chinese soy sauce. The characteristic patterns of amino acids and their contents of soy sause were easily obtained from the electropherograms within 60 s. In order to verify the reliability of method, the content was also calculated by traditional titration method. The hair hydrolysate was also added in the real sample to confirm the results. The recoveries of four samples were 97.2-116.0%, the RSDs of peak area were 0.64-4.45%, which indicatied the microchip electrophoresis was a simple and quick method for soy sauce quality detection.Chapter 6:We fabricate the integrated microchips with double helix mixing/reaction microchannels for on-line derivatization together with the electrophoretic separation. Efficient derivatization of aldehydes with ANTS could be performed on-line. Both reagents and sample solutions flowed through the reaction channel under the liquid level differences between the reservoirs and without any external pump. Our results proved that 5 aldehydes was successful derivatized with high reproducible analysis.30 consecutive injections relative standard deviations of peak areas were in a range of 0.28-1.61%. Finally, this method was applied for the determination of aldehydes in chocolate and infant cereal, the standard addition recoveries was 87.8-102.8%.