Integrated optical technologies for analytical sensing
Recent diversification of the telecommunications industry has resulted in the adaptation of optical materials and their associated fabrication technologies for use in the bioanalytical sensor industry. Flame hydrolysis deposited (FHD) planar silica is one such material. Capable of producing high quality films for optical waveguides, the chemical inertness of the deposited silica makes it an ideal substrate from which to fabricate a biological fluorescence sensor. The aim of the work contained in this thesis was to utilise the FHD silica in optical - fluorescence sensors suitable for use at visible and in particular red wavelengths where several fluorophores can be excited, and background fluorescence from the silica is small. New technologies for producing waveguides have been evaluated in the context of their usefulness in optical sensors, with the intention of producing devices with as few fabrication steps as possible to reduce fabrication time and cost. The design, fabrication and testing of a number of sensor configurations is described, in which optical waveguides were interfaced with microfluidic chambers to provide excitation of a fiuorophore in solution. New waveguide fabrication technologies were used for the first time in sensor systems with integrated microfluidic circuits. Waveguides, written by electron beam densification were evaluated in terms of their performance in splitting an excitation signal into several different components, as would be appropriate for excitation of multiple microfluidic chambers - an 'array sensor'. Both Y-branch waveguides and multimode interference (MMI) splitters were successfully used to split the excitation signal. In addition to electron beam densification, UV irradiation at a wavelength of 157 nm was used to write waveguides in FHD silica. The application of a metal surface mask to define the waveguide structures is described. To allow sensitive detection and identification of fluorophores from FHD silica sensor chips, a single chamber device was successfully interfaced to a system to make time resolved fluorescence measurements, a technique known as time correlated single photon counting (TCSPC). The use of TCSPC allowed measurement of the decay time of the fluorescent dye, by which different fluorescent molecules could be identified, as well as the possibility of low concentration measurements. The research has allowed new technologies for creating waveguides in FHD silica to be adapted for sensing purposes, leading to a platform for creating devices in a number of different configurations.