Modified plastic surfaces for high performance microfluidic immunoassay devices

The goal of this research is studies of surface modifications and bioconjugations for a plastic microfluidic device and to explore how these enhance the sensitive and specificity of the device in flow-through ELISA. The protein/poly-(dimethylsiloxane) (PDMS) interaction was studied. A new molecular level approach was developed using AFM to study the conformation and kinetics of the adsorption of protein A on a PDMS surface through investigations of the effects of pH values, protein concentrations, and contact times on the adsorption. To covalently immobilize protein on PDMS surface, (3-aminopropyl)– triethoxy silane (APTES) was used to add amino groups onto PDMS. Amino groups in the APTES were converted into carboxyl groups by reaction with succinic acid anhydride (SAA), then captured the protein through 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). Immunoglobulins (IgGs) were covalently immobilized onto the PDMS using the SAA/EDC surface treatments and examined through a well-organized competitive inhibition ELISA. Poly (vinyl alcohol) or PVA is one of the most hydrophilic polymers with stable chemical properties and good dissolution. A simple but effective technique was investigated to prepare a PVA-functionalized PDMS for suppressing non-specific adsorption of protein. Proteins were covalently immobilized on the PVA- functionalized PDMS surface for the development of a solid surface for immunoassays. A PVA-functionalized PDMS microfluidic ELISA device was fabricated and employed to detect important biomarkers, including HBsAg, HBeAg and α-FP, via a flow-through process. The methodology established in this research can provide a simple, fast and sensitive hepatitis B virus infection diagnoses tool. Dextran was investigated as a biocompatible polymer for cell repelling biomaterial coatings. PDMS was modified with a dextran solution to enhance PDMS surface hydrophilicity and furthermore to achieve high immobilization efficiency of proteins through dextran’s abundant hydroxyl groups. A dextran modified PDMS microfluidic ELISA device was fabricated with unique architecture for eliminating crossover interference. This microfluidic device was used to simultaneously detect multiple important biomarkers, which included IL-5, HBsAg, and IgG. Moreover, the fabricated dextran-modified PDMS device demonstrated its capability for colorimetric detection of proteins and results could be observed clearly by the naked eye.DOCTOR OF PHILOSOPHY (SCBE