Preparation and Characterization of Biologically Doped Sol-Gel Derived Nanocomposite Films Suitable for Biosensor Development

Abstract

<p>The entrapment of biomolecules within TEOS-based sol-gel derived organic/inorganic nanocomposite materials has proven to be a viable platform for the development of biosensors and solid-phase biocatalysts. In this thesis, a series of organically modified silica materials were prepared by a two-step aqueous processing method that was suitable for biomolecule entrapment, and were formed as submicron thick films by dipcasting. Dispersed additives, such as polymers (Class I materials) and covalently bound additives, such as organically modified silanes (Class II materials), were used to modify the internal environment compared to the undoped matrices and to correlate the properties of entrapped enzymes.</p> <p>The morphology of organically modified silica materials could be modified through the use of either separate or co-hydrolysis of the silane precursors, with the later method generating optically transparent materials. Fluorescence microscopy revealed chemical heterogeneity in materials that appeared to be homogeneous by brightfield or SEM.</p> <p>Fluorescence emission studies of a solvatochromic dye entrapped within the film confirmed that the internal chemical environment of the films was strongly affected by doping with polymers and organosilanes. The films showed a rapid initial change in chemical properties owing to solvent evaporation, followed by a much slower evolution over several months owing to continued condensation reactions within the film.</p> <p>A reagentless biosensor was designed based on co-entrapment of an enzyme and a fluorescently labeled polymer. The enzymes urease and lipase were selected for this study as both catalyze reactions that alter the local pH. By co-entrapping pH sensitive fluorophores (SNARF-I and fluorescein) bound to a high molecular weight polymer, it was possible to detect the analytes urea and glyceryl tributyrate using changes in the fluorescence intensity (fluorescein) or emission ratio (SNARF-l). By tuning the polarity of the matrix it was possible to optimize the sensitivity of the sensing film for both the polar and non-polar analyte.</p>