Characterisation and optimisation of novel Sol-Gel materials for luminescence-based 02 sensing
Higgins, Clare (2007) Characterisation and optimisation of novel Sol-Gel materials for luminescence-based 02 sensing. PhD thesis, Dublin City University.
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Current sensor trends, such as multi-analyte measurement, miniaturisation and printability, are important drivers for materials to be used in optical chemical sensors. In recent years, there has been a focus on sol-gel materials for sensor applications due to their excellent optical properties, ease of entrapment of analyte-sensitive dyes and the compatibility of the sol-gel process with a range of deposition techniques. This study focuses on the fabrication, characterisation and optimisation of novel sol-gel ORMOSIL (ORganically MOdified SILicate) matrices for luminescence-based O2 sensing. The O2 sensing scheme is based on the luminescence quenching of the highly 0 2 - sensitive ruthenium complex [Ru(II)-tris(4,7-diphenyl-l,10-phenanthroline) dichloride], entrapped in a porous sol-gel film. A phase fiuorometric detection scheme was employed which capitalised on the inherent advantages of frequency-domain rather than time- or intensity-domain measurements. This study focuses on optimisation of the O2 sensor response under a variety of headings including, sensitivity, dynamic range, photobleaching effects and sensor interferences caused by solvent vapour. Key film parameters include porosity and film hydrophobicity. These parameters are intimately related to the precursors used, in addition to sol-gel processing parameters. The xerogel microstructure was investigated using spectroscopic ellipsometry. 0 2 diffusion coefficients were also measured and the results were correlated to porosity and sensor sensitivity data. A study of the phase fiuorometric response as a function of LED modulation frequency highlighted the importance of optical filter selection in order to produce the optimum sensor response. It is clear from this work that the O2 sensitivity of the film can be tailored via the sol-gel precursor used. Furthermore, there is a general correlation between the hydrophobicity of the film and the length of the precursor alkyl chain. Good correlation was obtained between porosity, diffusion coefficient and O2 sensing data. Finally, the work highlights the versatility of the sol-gel route to provide application-specific materials, thereby providing solutions to a variety of sensing problems.
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