Modification Of Amphiphilic Oligopeptide Based Poly (methyl Methacrylate) Microfluidic Chip Surface

Poly (methyl methacrylate)(PMMA) is one of the most commonly used substrates for the microfabrication of microfluidic chips. However, the surface of PMMA is higly hydrophobic and not compatible with aqueous separation media, causing poor separation performance due to serious analyte adsorption on the channel surface. Thus, surface modification is a critical issue for plastic MCE devices in electrophoresis application.Physical adsorption coating or Dynamic coating represents a simple and convenient surface modification technique, which forms a coating layer of surface modifiers via the spontaneous adsorption of surface active molecules from solution onto solid surface. The commonly used surface modification materials include surfactants such as sodium dodecyl sulfate (SDS), n-dodecyl β-D-maltoside (DDM) and water-soluble polymers such as methyl cellulose (MC), hydroxyethyl cellulose (HEC) and polyethylene glycol (PEG). Generally, high concentrations of surfactants and water-soluble polymers are required to achieve high performance separations, which greatly increased viscosity and ionic strength of a running buffer, causing difficulties of buffer loading and rinsing, increase of Joule heating and denaturation of proteins and enzymes. At present, the commonly used surface modification materials have shown limited success on suppressing adsorption of proteins, which can negatively impact to the application of PMMA devices in protein analysis and proteomics.In this thesis we designed and synthesized amphiphilic oligopeptides with rich arginine and lysine as a new surface modification material by mimicking strong adsorption of proteins on the solid surface. The modification of PMMA surface with amphiphilic oligopeptides were systematically characterized and high-throughput separations of amino acids, peptides and basic proteins were achieved in PMMA chips dynamically coated with amphiphilic oligopeptides. These provide a possibility for deveolpemnt of novel surface modification materials and methods.In the first chapter, the research progress of the microfluidic chip, production materials, the modified method, common detector, separation modes, and applications as well as the aim and significance of this thesis were briefly reviewed.In the second chapter, the spontaneous adsorption of amphiphilic oligopeptides from aqueous solution onto a PMMA surface was characterized using various techniques. We found that amphiphilic oligopeptides a self-assemble fibrillar coating layer on the PMMA surface with good hydrophilicility and biocompatibility, showing a near-perfect resistance to the nonspecific adsorption of both small dye molecules and proteins. The possible mechanism for the high affinity of the amphiphilic oligopeptides on the PMMA surface was proposed. These foundings allows a promising alternative to address the nonspecific adsorption of ananlytes such as proteins.In the third chapter, dynamic coating using amphiphilic oligopeptide EAK16-II, EAR16-II, and EAKR16-II was investigated for suppression of analyte adsorption and electroosmotic flow (EOF) in a PMMA channel. The addition of0.5-1.0mg/mL amphiphilic oligopeptides in the running buffer obviously suppressed the nonspecific adsorption of FITC-labeled amino acids, oligopeptides, protein digests, and basic proteins on the PMMA surface, thus allowing high-performance separations. We proposed that amphiphilic oligopeptides are promising surface modification materials for minimazition of analyte adsorption on PMMA suface, which may broaden the application of PMMA chips in bioanalysis especially in proteomics.