Green Chemistry Based Surface Modification Of Polydimethylsiloxane Microfluidic Chip For Protein Electrophoresis

With the completion of the human genome project, biological science has entered the post-genome era. Proteomics study is one of key tasks in the post-genome research, which entails separation techniques with high throughput and efficiency. The separation of proteins is the foundation of proteomic studies. Unfortunately, existing methods for separating proteins still cannot meet such demanding requirements. It is necessary to develop new approaches for protein separation with reduced separation time, high separation efficiency and throughput. The emerging microfluidic technology has shown potentials in revolutionizing protein separation techniques with advantages of miniaturization, integration and automation. Among the most widely used microfluidic systems, polydimethylsiloxane (PDMS) based microfluidic chips provides a variety of advantages including impermeability to water, permeability to air, noncytotoxicity, capacity for optical and electrochemical measurement, easily coupling to mass spectrometry, and low cost. However, the hydrophobicity of PDMS seriously influences the results of protein separation. Thus, modification of PDMS surface has drawn attention of researchers to enchance the hydrophilicity of PDMS, to reduce protein adsorption and to inhibit electroosmotic flow for improved separation of proteins.This thesis reviews hot issues of current proteomic research and summarizes the development of protein separation methods based on microfluidic chips. After concluding the difficulty of protein separation using PDMS microfluidic chips, this article proposed the use of green chemical modification methods for PDMS modification and their applications in protein separation. In this thesis, the fabrication of PDMS microfluidic chips was optimized, and three strategies of PDMS surface modification were further developed:(1) The fabrication processes of SU-8 negative epoxy mold and the curing of PDMS sheet were optimized, resulting in PDMS microfluidic chips with smooth vertical internal surface.(2) An amide-PEG based environmentally friendly surface modification strategy was developed for PDMS microchips to prevent protein adsorption and to enhance separation performance. During the surface modification, water was used as a clean solvent, and the whole surface modification procedure was conducted at room temperature. Fourier-transform infrared absorption by attenuated total reflection and contact angle measurements verified the efficient grafting of amino-PEG onto PDMS surface. Electroosmotic flow measurements were conducted to investigate the suppression of electroosmotic flow. Protein adsorption evaluation showed the ability of nonspecific protein adsorption after PDMS surface modification. Comparison of electrophoresis of protein using PDMS microchips before and after surface modification was further investigated.(3) "Click" chemistry based surface modification strategy was developed for PDMS microchips to enhance separation performance for proteins. Alkyne-PEG was synthesized and "click" grafted to azido-PDMS. During the surface modification, water was used as a clean solvent, and "click" surface modification procedure was conducted at room temperature. Fourier-transform infrared absorption by attenuated total reflection and contact angle measurements verified the efficient grafting of PEG onto PDMS surface. Electroosmotic flow measurements were conducted to investigate the suppression of electroosmotic flow. Protein adsorption evaluation showed the ability nonspecific protein adsorption after PDMS surface modification. Comparison of separation of proteins using PDMS microchips before and after surface modification was further investigated.(4) A biocompatible "grafting from" chemistry based surface modification strategy was developed for PDMS microchips to improve separation performance for proteins. Allyl-PEG was synthesized by a conventional procedure and "grafting from" PDMS surface. During the surface modification, water was used as a clean solvent, and surface modification procedure was conducted at room temperature. Fourier-transform infrared absorption by attenuated total reflection and contact angle measurements verified the efficient grafting of PEG onto PDMS surface. Electroosmotic flow measurements were conducted to investigate the suppression of electroosmotic flow. Protein adsorption evaluation showed the ability nonspecific protein adsorption after PDMS surface modification. Comparison of separation of proteins using PDMS microchips before and after surface modification was further investigated.Fourier-transform infrared absorption by attenuated total reflection was performed to prove successfully surface modification of all the surface modification strategies. Contact angle measurements proved that the PEG-functionalized PDMS surface became hydrophilic within 30 days. Electroosmotic flow measurements results verified the significant suppression of PEG-functionalized PDMS and sustainable electroosmotic flow regulation of PEG-functionalized PDMS microchips within 30 days. Flurescence protein adsorption investigation evaluated protein adsorption of PDMS microfluidic chips before and after surface modification. Comparison of protein separation using PDMS microfluidic chips before and after surface modification, results suggested the PEG-functionalized PDMS microfluidic chips significantly improved protein separation performance.