The Study Of Modification For PDMs Microchip Channel And Its Application In The Separation Of Amino Acids

Recently, microchip capillary electrophoresis system is becoming a newly rapidly developed research technology and has an extensive application perspective. Meanwhile, it has won an increasing attention and provided a powerful platform for analytical chemistry due to its reduced time for analytical process, high sample throughput, low consumption of samples and reagents, easy integration and automatically control. Polydimethylsiloxane (PDMS) has become a popular material for building multifunctional microfluidic devices mainly due to its good optical transparency, easy sealing with other materials, nontoxicity, low cost, easy fabrication, increasing versatility, relatively low curing temperature and good biocompatibility. However, PDMS microfluidic device employed for microchip capillary electrophoresis also shows some defects which hinder its application scope in life science. These defects include the low density of charge on the surface of PDMS microchip, the unstable electroosmotic flow (EOF), extreme hydrophobicity of PDMS microchip, easy adsorption of analytes onto the microchip channel surface, etc. To overcome the above defects, surface modification techniques have been developed to improve the surface properties of PDMS in this work, which were as follows.1. A facile, environmentally friendly and economical method based on in situ chemically induced synthesis strategy was developed for the modification of a PDMS microchip channel surface with polydopamine/gold nanoparticles (PDA/Au NPs) to create a hydrophilic and biofouling resistant surface. Here, dopamine (DA) as reductant and monomer, and HAuCl4as oxidant to trigger DA self-polymerization and the source of Au NPs, were filled into PDMS microchannel to immobilize well-distributed and robust PDA/Au NPs coating onto the surface of PDMS microchip channel by the in situ chemically induced strategy. Compared with the native PDMS microchip channel, the modified one exhibited high stability and suppressed EOF, much better wettability, and less nonspecific adsorption towards five amino acids. Fast and efficient separation of five amino acids such as arginine (Arg), proline (Pro), histidine (His), valine (Val) and threonine (Thr) suggested greatly improved electrophoretic performance on the PDA/Au NPs-coated PDMS microchips.2. In this work, we present the first application of BSA-conjugated graphene-based magnetic nanocomposite (GO/Fe3O4/BSA) as a novel stationary phase of OT-CEC for efficient enantioseparation. Firstly, GO/Fe3O4nanocomposites were synthesized by in situ chemical precipitation method. The resulting GO/Fe3O4nanocomposite is endowed with the excellent properties of the two independent components, such as the high adsorption capacity of graphene and the magnetic nature of Fe3O4NPs, which is favorable for the further immobilization of biomolecules and easy retrieval and separation of graphene from dispersion. BSA was then immobilized on GO/Fe3O4through hydrophobic, π-π stacking interactions and hydrogen bonding to form a multicomponent nanocomposite and subsequently organized by an external magnetic field in the PDMS microchannel. The preparation of the GO/Fe3O4/BSA conjugate was characterized by scanning electron microscopy, X-ray diffraction, UV-vis spectra and the contact angles. The electrochromatographic enantioselectivity and reproducibility of the constructed OT-CEC microdevice was validated by chiral separation of tryptophan enantiomers. Parameters affecting the separation efficiency were investigated in detail. The results proved that the method had a good performance in terms of sensitivity, repeatability and efficiency for the separation of tryptophan enantiomers.3. An enantioselective microfluidic device was prepared by molecular imprinting technique based on self-polymerization of DA in the presence of template L-tryptophan (L-Trp) on the Fe3O4nanoparticles (Fe3O4NPs) surface to improve the separation effect for chiral amino acids. We used DA self-polymerization to form thin, surface-adherent, PDA films onto the Fe3O4NPs surface. During the self-polymerization of DA, some template molecules were embedded in the PDA layer. After the removal of these embedded template molecules, the targeted molecules imprinted sites are created. Then, the imprinted nanoparticles (MIP-Fe3O4@PDA NPs) could be localized as stationary phase in the microchannel of microfluidic device with the help of an external magnetic field. To evaluate such a strategy was possible to realize ideal chiral separation in PDMS microchip channel. The recognition properties of microchannels were characterized by the separation of D/L-Trp. The result showed that D/L-Trp were baseline separated in a3.7cm separation channel within80s with theoretical plates about269,0000and285,0000plates/m for D-Trp and L-Trp, and Rs of about1.68under the optimized preparation and electrochromatographic conditions.4. Chirality is one of the significant attributes in the nature. However, in the study field of the recognition and separation of enantiomers, the selection and use of the chiral selector is the key to success. Here, we present the first application of PDA as as the chiral selector for the recognition and separation of enantiomers in PDMS microchip channel. Inspired by the air-driven chemical polymerization of DA can be polymerized to PDA coatings on various surfaces under alkaline conditions. We used DA self-polymerization to form thin, surface-adherent films with the thickness of PDA about20nm onto the Fe3O4NPs surface. In order to evaluate the chiral selection properties for PDA, the prepared Fe3O4@PDA NPs were localized as stationary phase in the PDMS microchannel with the help of an external magnetic field. The test results showed that we have successfully constructed the chiral selective functional PDMS microchip channel based on PDA, the chiral molecules of amino acids, peptides, and drugs obtained the effective separation in PDA@Fe3O4NPs modified PDMS microchip channel. Therefore, the present PDA can be used as a chiral selector for the separation of chiral molecules in our experiments. It not only broadens the selection range of chiral selector, but also provides a simple, effective chip-based capillary electrophoresis for chiral separation and analysis method.