Its Dynamic Modification Coating Microfluidic Chip In Oligo Polysaccharides Isolated Application PDMS

Carbohydrates, one of the four major classes of biomolecules along with proteins, nucleic acids, and lipids, make up most of the organic matter on earth. Carbohydrates serve as the main energy stores and fuels as well as structural elements in the cell walls of animals and plants, and also play key roles in mediating cell-cell recognition and interactions of cells with the cellular environment. Oligosaccharides from various natural sources such as glycoproteins and Chinese herbs are complex compounds with subtle differences in structure, such as carbohydrate sequence, types of glycosidic bonds, and number and position of branched chains, remaining analysis of complex oligosaccharides a very challenging task. Therefore, development of high-resolution analytical method is of great importance for carbohydrate chemistry.Microchip CE (MCE) is a high-performance analytical technology based on microfluidic chips, showing intrinsic characteristics of high speed, high throughput, negligible sample/reagent consumption, and easy integration and automation. Poly(dimethylsiloxane)(PDMS) has become one of the most commonly used substrates for the microfabrication of microfluidic devices mainly to its excellent optical characteristics, low cost, easy processing and mass production. However, PDMS show some defects including extreme hydrophobicity, unstable electroosmotic flow (EOF), and serious adsorption of analytes, leading to the poor separation performance of PDMS chips. To overcome the above defects, various surface modification approaches have been employed to manipulate EOF and minimize analyte-wall interactions and thus improve the separation performance of PDMS chips. We focused on the dynamic coating of PDMS chips with various surface modifiers for high-performance analysis of complex oligosaccharides in this thesis as follows.1. We briefly review the principles, characteristics, and recent developments of MCE. The substrate materials, fabrication techniques, and detection methods in MCE are then summarized. Finally, the advantages and disadvantages of PDMS chips and the surface modification techniques for PDMS chips surface are briefly discussed. Dynamic coating of PDMS chips with various surface modifiers was employed to minimize analyte-wall interactions and EOF for high-performance separation of complex oligosaccharides in this work. 2. Using oligosaccharide ladder of acidic hydrolysate of dextran T-40labeled with8-aminopyrene-1,3,6-trisufonate (APTS) as model carbohydrates, dynamic coating of PDMS with sodium dodecyl sulfate (SDS), hydroxyethyl cellulose (HEC), and methyl cellulose (MC) were systematically investigated. The test of fluorescence intensity and contact angle experiments show that modified microchip can improve the hydrophilic of surface and enhance the biological compatibility by0.5%MC. We found that0.5%MC considerably improve the hydrophilicity and biocompatibility of PDMS surface. No visible adsorption of APTS-labeled oligosaccharides was observed on PDMS channel surface and the water contact angle decrease from97.5±1.6°on a pristine PDMS surface to42.7±0.8°on MC-coated PDMS surface. Optimization studies have also been performed with respect to the conditions of dextran hydrolysis, APTS labeling, and MCE separation. Under the optimum conditions, high-performance separation of oligosaccharide ladder and crude oligosaccharides PGPI, PGPII, PGPIII from pomegranate peel extracts were achieved on a PMDS channel dynamically coated with0.5%MC. The current MCE-based method might be a promising alternative for analysis of carbohydrate complex from Chinese herbs.3. A novel amphiphilic oligopeptide EAK16-Ⅱ was investigated for dynamic coating of PDMS chips. We found that EAK16-Ⅱ forms fibrillar self-assembles on the PDMS surface, resulting in a stable coating layer with good hydrophilicity and biocompatibility. The contact angle decrease from97.5±1.6°on a pristine PDMS surface to36.2±1.4°on a1.0mg/mL EAK16-Ⅱ-coated PDMS surface, and no adsorption of APTS-labeled was observed on an EAK16-Ⅱ-coated PDMS surface. Under the optimum conditions, the rapid and efficient separation of APTS-labeled carbohydrate isomers, oligosaccharides ladder and crude polysaccharides from pomegranate peel were achieved. Compared to the commonly used surface modifiers such as water-soluble polymer MC and surfactants SDS, amphiphilic oligopeptide EAK16-Ⅱ is neutral over a large pH range with a low molecular weight and minute amounts of less than1%DDM do not change the properties of a running buffer such as viscosity and ionic strength. We proposed that amphiphilic oligopeptides are promising surface modifiers for surface modification of PDMS chips.