The Study Of Modification For PDMS Microchip And Its Application In The Separation Of Chiral Amino Acids

Chirality is one of the universal phenomena existing in the nature and living organisms, especially reactive molecules in the body and natural products. The study of chirality plays an important role in many fields, such as life sciences, materials and pharmaceutical science. The special structure of chiral molecule makes its properties uncommon. For example, they have very different pharmacological properties and bioactive effects in biological environments. Thus, the enantioseparation of enantiomers has become vitally significant. Microchip capillary electrophoresis (MCE) is a novel analytical method. Compared with traditional methods, MCE owns many advantages, such as reduced time for analytical process, low consumption of samples and reagents, high separation efficient, easy automatically control and integration. Polydimethylsiloxane (PDMS) has become a popular material for fabricating multifunctional microfluidic devices due to its nontoxicity, good optical transparency, low cost, easy sealing with other materials and low curing temperature. However, the hydrophobicity and uncontrolled EOF of native PDMS is a major obstacle for the application in microfluidic devices. It may lead to non-specific adsorption of hydrophobic analytes, peak tailing and low separation efficiency. In this work, surface modification techniques were provided to improve the stability of EOF, the surface wettability for facilitating liquid delivery and decreasing non-specific adsorption of hydrophobic analytes, which were as follows.1. A novel, simple, and economical method for the preparation of chiral stationary phases for chip-based enantioselective open tubular capillary electrochromatography (OT-CEC) using polydopamine (PDA) coating as an adhesive layer was reported for the first time. After the poly(dimethylsiloxane)(PDMS) microfluidic chip was filled with dopamine (DA) solution, PDA film was gradually formed and deposited on the inner wall of microchanneL Due to possessing plentiful catechol and amine functional groups, PDA coating can serve as a versatile multifunctional platform for further secondary reactions, leading to tailoring of the coatings for protein bioconjugation by the amines and thiols via Schiff base or Michael addition reactions. Bovine serum albumin (BSA), acting as a target protein, was then stably and homogeneously immobilized in the PDA-coated PDMS microchannel to fabricate a novel protein stationary phase. Under a mild condition, D-and L-tryptophan were efficiently separated on the PDA/BSA-coated PDMS microchips.2. In this work, a novel chip-based enantioselective open-tubular capillary electrochromatography (OT-CEC) was developed employing bovine serum albumin (BSA) conjugated polydopamine-graphene oxide (PDA/GO) nanocomposites (PDA/GO/BSA) as stationary phase. After the poly(dimethylsiloxane)(PDMS) microfluidic chip was filled with a freshly prepared solution containing dopamine (DA) and graphene oxide (GO), PDA/GO nanocomposites were formed and deposited on the inner wall of microchannel as permanent coating via the oxidation of DA by the oxygen dissolved in the solution. Bovine serum albumin, acting as a target protein, was stably and homogeneously immobilized in the modified PDMS microchannel to fabricate a protein-stationary phase. Compared with the native PDMS microchannels, the PDA/GO/BSA-modified surfaces exhibited much better wettability, more stable electroosmotic mobility, and less nonspecific adsorption. Under a mild condition, D-and L-tryptophan were efficiently separated with a resolution of1.57within only1min on the PDA/GO/BSA-coated PDMS microchip.3. Chip-based enantioselective open-tubular capillary electrochromatography (OT-CEC) with β-cyclodextrin (P-CD) conjugated graphene oxide-magnetic nanocomposites (GO/Fe3O4NCs) as stationary phase was developed for the first time. The resultant GO/FesO4/β-CDNCs not only have the magnetism of Fe3O4NPs that make them easily manipulated by an external magnetic field, but also have the larger surface which can incorporate much more chiral selector molecules. Compared with the native PDMS microchip, the GO/Fe3O4/β-CD NCs-modified surfaces exhibited more stable and suppressed electroosmotic mobility (EOF), and less nonspecific adsorption towards analytes. Successful baseline separation of tryptophan enantiomers was achieved in less than50s. Factors that affect the enantioseparation resolution were examined. These results show that the use of GO/Fe3O4/β-CD NCs within microfluidic channels hold great promise for a variety of analytical schemes.