Surface plasmon resonance quasi-distributed polymer optical fiber sensor for oxygen detection

This thesis explores the development of a quasi-distributed polymer optical fiber (POF) sensor for oxygen detection, utilizing surface plasmon resonance (SPR) and fluorescence-based techniques to enhance performance and versatility. The sensor design incorporates a silver (Ag) coating to amplify SPR effects, paired with fluorescence dyes which are platinum octaethylporphyrin (PtOEP) and 5,10,15,20-tetrakis (pentafluorophenyl) 21H,23H-porphine palladium (II) (PdTFPP), and Tris (4, 7-diphenyl-1, 10-phenanthroline) ruthenium (II) dichloride ([Ru(dpp)3]2+), for photostability and responsiveness to oxygen. The sensing region of the POF was prepared by stripping the cladding to expose the core, allowing direct interaction with the environment. A silver (Ag) coating was then applied to the exposed fiber surface to facilitate SPR excitation, followed by deposition of fluorescent dyes. The sensor's performance was assessed through a custom experimental setup that included precise oxygen and nitrogen flow control, dye-specific laser excitation which are 385 nm, 405 nm, and 450 nm for PtOEP, PdTFPP, and [Ru(dpp)3]2+, respectively. The emission peaks of the fluorescent dyes were recorded at 646.77 nm for PtOEP, 668.62 nm for PdTFPP, and 600.07 nm for [Ru(dpp)3]2+, ensuring effective fluorescence detection and differentiation. When SPR was implemented using the Ag coating, significant shifts in the emission peaks were observed due to the enhanced plasmonic interaction between the metal layer and the fluorescent dyes. For PtOEP, the emission peak shifted from 646.77 nm to 668.1 nm, while for PdTFPP, the peak shifted from 668.62 nm to 668.29 nm. Similarly, the emission peak for [Ru(dpp)3]2+ shifted from 600.07 nm to 550.76 nm. The sensitivity of the fluorescent dyes was measured in terms of the change in fluorescence intensity per unit of oxygen concentration. Without SPR enhancement, the sensitivity values were 0.0324 a.u/% for PtOEP, 0.0994 a.u/% for PdTFPP, and 0.0268 a.u/% for [Ru(dpp)3]2+, highlighting PdTFPP as the most sensitive dye in thefluorescence-only configuration. When SPR was introduced, the sensitivity of the SPR-enhanced configuration was calculated based on the wavelength shifts observed inresponse to varying oxygen concentrations. The sensitivity improved significantly,with 0.0367 nm/% values for Ag/PtOEP, 0.1045 nm/% for Ag/PdTFPP, and 0.0312nm/% for Ag/[Ru(dpp)3]2+. Finally, in the quasi-distributed configuration, Ag/PdTFPPshowed the highest sensitivity at 0.1317 nm/%, followed by Ag/PtOEP with moderatesensitivity at 0.048 nm/%, while Ag/[Ru(dpp)3]2+ exhibited the lowest sensitivity at0.0191 nm/%. Distinct excitation peaks validated the effective interaction of dyes withrespective laser wavelengths, confirming the multi-point sensing capability of the quasi-distributed configuration. The sensor exhibited robust real-time performance, achievinghigh sensitivity and reliable detection across multiple locations along the fiber. Theseadvancements demonstrate the system's potential for scalable, distributed sensing indiverse applications, including environmental monitoring, medical diagnostics, andindustrial safety.