Investigation of poly(ethylene glycol) hydrogel networks for optical biosensing

This dissertation describes the development and characterization of a fluorescence biosensor based on photopolymerized poly(ethylene glycol) (PEG) hydrogel microparticles incorporating a fluorophore modified polysaccharide ligand and a fluorophore modified glucose binding protein chemically conjugated into the hydrogel network using an α-acryloyl, ω-N-hydroxysuccinimidyl ester of PEG-propionic acid. The goal was the design and development of injectable, fluorescent-doped, intradermal polymer transducers that could be combined with an optical probe to quantify blood glucose levels. These polymer microspheres would operate by being injected below the skin of diabetic patients. After implantation, the glucose specific fluorescently tagged polymer, when non-invasively illuminated, would provide fluorescence signals proportional to interstitial glucose concentration.; The sensing scheme utilized was based upon competitive binding between concanavalin A and dextran. In the absence of glucose, TRITC-Con A binds with FITC-dextran, and the FITC fluorescence is quenched through fluorescence resonance energy transfer. Competitive glucose binding to TRITC-Con A liberates FITC-dextran, resulting in increased FITC fluorescence proportional to the glucose concentration. This sensing scheme was explored using microencapsulation within alginate/lysine microcapsules, and through immobilization within a poly(ethylene glycol) hydrogel. In vitro experiments of active spheres suspended in a buffered glucose solution was used to quantify sensor response. An additional biosensing scheme was examined by incorporating fluorescently-labeled organophosphorus hydrolase, an enzyme which catalyzes neurotoxins. Gel fluorescent response was examined in the presence of paraoxon.; PEG hydrogel mass transfer characteristics were characterized by examining swelling behavior and small molecular weight (MW) penetrant uptake. Average polymer mesh sizes were estimated from the swelling behavior. Diffusion coefficients for small MW analytes were calculated from the penetrant uptake rate.; Monte Carlo simulations were used to simulate the influence of particle size, scattering and absorption coefficients, and quantum yield upon the fluorescent signal strength of a packed bed of particles. Simulation results provided insight into how hydrogel parameters could be altered to maximize signal intensity while minimizing implant thickness.; Finally, self-assembly of PEG chains with an amine-terminated polymer using Michael addition was examined to developing PEG thin film biosensors.