Fibre optic chemical sensors for non-fluorescent analytes using fluorescence quenching and waveguide Raman spectroscopy

Fibre-optic chemical sensors were developed for oxygen and chlorinated hydrocarbons using fluorescence quenching method and solid-phase microextraction (SPME) waveguided Raman spectroscopy.; The first project involved the determination of gaseous and dissolved oxygen based on the quenching of fluorescence emission of indicating dyes such as tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate. The indicating dye was immobilized in a cross-linked polydimethylsiloxane (PDMS) film by dissolution of the dye in a solution of polymer precursor material. A film was then solvent-deposited on the end of an optical fibre. The sensor has been tested in the gas-phase, in aqueous solution, in presence of possible interferents, and after steam-sterilization to illustrate the durability and versatility of the PDMS matrix. A novel optical configuration was used to incorporate a blue light-emitting diode for excitation while the detection film was at the end a single fibre. A plot of fluorescence response using the Stern-Volmer equation, Fo/F = 1 + Ksv [O2], was used for the calibration of the response. Stern-Volmer plots were generally non-linear due to the presence of background signal. The linearity was improved by background subtraction. A simplified 2-point calibration scheme was proposed based on this modified Stern-Volmer plot. The characterizations and performance of this novel sensor in the gaseous and liquid phases is presented in the current study.; The second project involved the design and the characterizations of a fibre-optic laser Raman sensor for trace level chlorinated hydrocarbons in water by integration of a polymer-based SPME waveguide medium. Pre-concentration of the target compounds is achieved by immersing a polydimethylsiloxane (PDMS) cylindrical waveguide (∼1 mm dia.) either directly into the test solution or in the headspace and waiting for analytes to partition into the PDMS phase. After equilibration, the Raman spectrum inside the PDMS rod provided a three to four order of magnitude signal enhancement over that detected in bulk solution. The PDMS rod not only served as a pre-concentration medium, but also a waveguide which increased the effective optical sampling path length and further enhanced the analyte Raman signal. Calibration curves were measured for each of the target compounds using SPME waveguided Raman sampled in headspace. The limits of detection for perchloroethylene and dichloroethylenes were at sub-ppm levels, whereas trichloroethylene's was around 5 ppm. Signal dependence on parameters such as laser power and waveguide length were also studied.