Functional Polymers for Biosensing Applications
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The work presented in this dissertation involves two separate systems. The first system was the investigation of photonic crystals as a chemical and biosensing platform. The second investigation was the fabrication of a point-of-care blood ammonia sensor. The photonic crystal fabricated was composed of the block copolymer polystyrene-b-poly(2-vinylpyridine)(PS-b-P2VP), which when cast into films, self-assembles into a multilayer structure. The P2VP block of the multilayer structure can be quaternized, causing it swell in aqueous media, providing the necessary spacing for it to operate as a 1D photonic crystal for visible wavelengths of light. The reflected wavelength or color of the photonic crystal is dictated by its spacing. Boronic acid functionalities were covalently attached to the P2VP block, which imparts the ability to bind to sugar molecules. When boronic acids bind sugars, such as fructose, the acid ionizes and becomes negatively charged, causing the P2VP block to swell, and changing the reflected color of the photonic crystal. In the following studies the covalent attachment of boronic acid to PS-b-P2VP was characterized. The resulting photonic crystal was then evaluated as a sensitive fructose sensor with a detection limit of 500micromolar. A novel method for the covalent attachment of primary amines to the P2VP block was also investigated. In Chapter 4, the utilization of trimethylsilyl amine protecting groups, allowed for the chemical modification of P2VP with primary amines without compromising the microphase separated nanostructure of the PS-b-P2VP. The primary amine functionality was characterized and shown to be reactive with cross-linking agents such as glutaraldehyde. A point-of-care blood ammonia sensor was engineered utilizing a specific, colorimetric ammonia reaction, termed the indophenol reaction, in conjunction with a cation exchange membrane(CEM). The membrane allowed for the rapid extraction of ammonium ions from whole blood. The extracted ammonia solution was then used with the indophenol reaction, which generates a blue color in the presence of ammonia. The sensor could extract ammonia in 20 minutes and had a detection range of 25-500micromolar in whole human blood with a COD of 0.9573.