TY - THES ID - 135382145 TI - Hollow Sphere Colloidal Photonic Crystals: Enhancing fluorescence quenching based dissolved oxygen detector AU - Mazzei, Leandro AU - Clays, Koen AU - KU Leuven. Faculteit Wetenschappen. Opleiding Master in de chemie (Leuven) PY - 2023 PB - Leuven KU Leuven. Faculteit Wetenschappen DB - UniCat UR - https://www.unicat.be/uniCat?func=search&query=sysid:135382145 AB - The concentration of dissolved molecular oxygen (DO) plays a vital role in various sectors including industrial production, aquaculture, food production, environmental monitoring, metabolism. While there are three popular methods to detect the concentration of DO, namely, the iodometric method, the electrochemical method, and the optical method, only the optical method allows for real-time measurements without oxygen consumption. This method is based on fluorescence quenching, where the collisional quenching of DO causes the excited state of fluorophore in water to return to the ground state. The fluorescence lifetime of the fluorophore is inversely proportional to the concentration of DO, as described by the Stern-Volmer equation. By artificially increasing the fluorescence lifetime of the fluorophore, it is possible to amplify the detection scale and, consequently, enhance detection sensitivity. Fermi's golden rule states that the spontaneous emission rate of a quantum emitter weakly coupled to a structured photonic reservoir is determined by the local density of photon states (DOS) at the emitter's position and wavelength. By creating a photonic crystal (PC) acting as a photonic reservoir and carefully engineering its photonic bandgap (PBG) to match the emission wavelength of the fluorophore, it is possible to reduce the emission rate of the fluorophore, resulting in an increased fluorescence lifetime. The PBG of a PC, which exhibits periodicity in its refractive index (RI), reduces the DOS within its bandgap. However, a challenge arises when the traditional solid sphere based colloidal photonic crystals (CPCs) is immersed in water, as RI matching can occur, thereby diminishing the PBG effect. This issue can be resolved by using hollow colloidal spheres instead of solid spheres as the building blocks of the PC. In this thesis, the objective was to enhance the measurement sensitivity of a fluorescence quenching-based oxygen detector by engineering hollow sphere colloidal photonic crystals (HSCPCs) and applying them to the DO detection process. To achieve this goal, HSCPCs were synthesized by creating a polystyrene (PS) template sphere coated with silica via Stöber condensation. These core-shell particles were then self-assembled into a CPC structure and subjected to calcination in an oven to remove the PS core. The most challenging aspect of this process was to create an HSCPC with a PBG that matched the fluorescence wavelength of the fluorophore. After several attempts, the desired HSCPC was successfully fabricated. The characterization of these HSCPCs involved reflectance measurements, scanning electron microscopy, and transmission electron microscopy. Upon completion of the synthesis, optical fluorescence lifetime measurements confirmed that the HSCPCs effectively increased the fluorescence lifetime of the fluorophore. Furthermore, it was observed that the HSCPCs significantly enhanced the detection scale by nearly 200%, thereby improving measurement sensitivity, which was the primary objective of this thesis. ER -