Photonics sensing enabled by multimaterial and multifunctional fibers

• Main Author: Qi, Miao
• Other Authors: Wei Lei
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials; Engineering::Nanotechnology
• Online Access: https://hdl.handle.net/10356/155232
• Institution: Nanyang Technological University

Fiber-optic localized surface plasmon resonance (LSPR) sensors realized by depositing metallic nanoparticles on various fiber structures have captured intensive research attention in recent years due to their high degree of integration, high sensitivity, flexibility, and remote sensing capability. Modified with macrocyclic molecules, metallic nanoparticles possess improved biocompatibility and highly efficient biomolecule immobilization and recognition via host-guest interaction. As a macrocyclic molecule, β-cyclodextrin (β-CD) has a cavity structure and can form stable complexes with various guest molecules. In this thesis, high-quality and monodisperse β-CD-capped gold nanoparticles (AuNPs) are synthesized in a one-step facile and eco-friendly process, where β-CDs serve as both reductants and capping agents without introducing harsh reagents. The β-CD-capped AuNPs are integrated with a microfiber through electrostatic interaction. Owing to the host-guest interaction between β-CD and cholesterol, the fabricated fiber-optic LSPR sensor delivers an ultralow detection limit of cholesterol molecules of 5 aM. The selective recognition of the proposed biosensor to cholesterol is further verified by interference study. The recovery experiments in human serum samples also show credible results. Next, different from conventional LSPR sensors that are typically based on the sensing mechanism that the resonance peak variation is induced by the ambient refractive index change on the immobilized metal nanoparticles. In this thesis, a dynamic “react-and-cut” sensing mechanism that actively tailors the quantity of AuNPs on a fiber surface is proposed, in which supramolecular chemistry and organic chemistry are combined in fiber-optic LSPR sensors. Also, the proposed sensor is demonstrated with glutathione detection. To be specific, a compound with a triethoxysilyl (TES) and an adamantane group connected by a disulfide bond is synthesized. The molecules are then functionalized on the surface of a microfiber by silicon-oxygen bonds, and β-CD-capped AuNPs are decorated on the microfiber by the host-guest interaction between β-CD and adamantane. The dynamic sensing is based on the fact that the sulfhydryl groups on glutathione first react with and then break the disulfide bonds. As a result, AuNPs are detached from the fiber surface, introducing the change of plasmonic behavior. This integrated fiber-optic LSPR sensor delivers a unique mechanism by cutting off AuNPs rather than the adsorption of analytes, providing more design space to achieve vast sensing platforms. In addition to the aforementioned silica fibers adopted in LSPR sensors, elastic and stretchable optical fibers have received extensive attention due to their high flexibility, dynamic bending elasticity and mechanical toughness. Recently, self-healing materials that can recover their physical properties after being subjected to external damage have been used to fabricate elastic and stretchable optical fibers. In this thesis, a transparent thermoplastic polyurethane (TPU) elastomer with high tensile strength and toughness is synthesized through step-growth polymerization. The synthetic TPU achieves superior self-healing capability by facile aromatic disulfide metathesis. After being shaped into a preform with an appropriate shape, the self-healing TPU optical fiber is manufactured via thermal drawing technique. This is the first time self-healing fibers have been prepared by thermal drawing technique with large-scale production capacity. Subsequently, the self-healing speed of TPU optical fiber is investigated through the transmission spectrum variation during the whole healing process. This provides a novel method to characterize self-healing materials, and it is expected to provide a unified standard for quantitatively studying the speed and efficiency of self-healing behaviors. Last, TPU optical fibers with different peak absorption are obtained by doping with organic dyes. Harness the self-healing and stretchable properties of TPU, dye-doped fibers are spliced together to fabricate a distributed strain sensor.