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There has been an increasing demand in recent years from a wide variety of industries for sensors which combine high sensitivity, fast response, compact size and low power consumption. Tapered optical microfibres can generate easily accessible evanescent fields with a large intensity and short decay distance which make microfibres very suitable candidates as the basis of sensors to suit a variety of application areas. In this thesis, experimental research is presented concerning the development of sensors using structures based on tapered optical microfibres, with a particular emphasis on biochemical sensing applications. Light propagation along an optical microfibre depends on its shape, diameter and surface roughness. A microfibre fabrication setup developed as a key prerequisite to the research undertaken, that utilized an adapted microheater brushing and tapering technique is described. The setup allows for the fabrication of microfibres and related structures with controllable taper shapes and diameters. There is a tradeoff between sensitivities and microfibre diameters (which directly affects the robustness of the microfibre structures) for microfibre based sensors. To mitigate this tradeoff, two microfibre based structures were chosen and investigated for sensor development in the research reported in this thesis. The first structure was an optical microfibre coupler. Such an optical microfibre coupler, which has environment dependent coupling coefficients in addition to easily accessible evanescent fields, is a simple and efficient structure for sensing. A refractive index sensor with a maximum sensitivity of 4155 nm/RIU was developed using an optical microfibre coupler. Utilizing the structure’s refractive index sensitivity, a humidity sensor was developed by coating a microfibre coupler with a layer of humidity sensitive polymer. A biosensor was also developed by immobilizing a bio-receptor on the surface of a packaged microfibre coupler. The ability of the developed biosensor to detect the specific binding between an antibody-antigen pairing for potential applications in clinical diagnostics was demonstrated and is reported in this thesis. The second structure was a tapered optical microfibre which incorporates gold-silver alloy nanoparticles. By immobilizing nanoparticles onto the surface of a tapered optical. microfibre to generate localized surface plasmon resonances, sensitivity enhancement can be achieved for microfibres with relatively large diameters, which has the benefit of being more mechanically robust. The use of gold-silver alloy nanoparticles with different alloy formulations can offer the extra advantage of tunable physicochemical properties. The localized surface plasmon resonance effects were investigated and compared for sensor samples incorporating nanoparticles with different alloy formulations. As an example of a sensing application using the structure, a novel pH sensor was demonstrated by coating the immobilized nanoparticles with a pH sensitive polyelectrolyte multilayer film..
Bo, Lin. (2015). Tapered Optical Microfibre Based Structures for Sensing Applications. Doctoral Thesis, Technological University Dublin. doi:10.21427/D71889