Author:

Abstract:

Volatile organic compounds (VOCs) are chemicals found in various settings, including domestic, and industrial environments, originating from natural and human-made sources. Due to their potential harm to health and the environment, detecting and monitoring VOCs is crucial. While gas chromatography with mass spectrometry is the preferred method, it is expensive and unsuitable for real-time on-site measurements. To address this issue, this Ph.D. project aimed to create an economical and versatile VOC sensor. The approach involved functionalizing fiber-optic surface plasmon resonance (FO-SPR) sensors with metal-organic frameworks (MOFs). MOFs are known for their stable and versatile structures with selective adsorption capabilities of gaseous compounds such as VOCs and, thus, introduced the necessary selective enrichment on the FO-SPR sensors for VOC detection. This dissertation opens with a comparative investigation of all sensing principles used to identify VOCs. The focus then transitions to the FO-SPR sensing technique specifically, explaining its fundamental principles and distinctive qualities that render it a promising approach for VOC sensing. In addition, a thorough examination of MOFs is undertaken to explore their capability for selective adsorption of VOCs, discussing their structure, chemistry, and synthesis techniques, with a focus on their compatibility with FO-SPR sensors. This knowledge was implemented in a practical study of selective VOC detection using FO-SPR sensors functionalized with MOFs, ZIF-8 and ZIF-93 specifically. The study successfully detected various alcohols at ppm concentrations, revealing distinct responses between ZIF-8 and ZIF-93 functionalized sensors establishing the concept of MOF functionalized FO-SPR sensors as a suitable concept for real-world VOC sensing applications. Though successful, the former study utilized a conventional analysis approach that reduced the FO-SPR spectrum to a single wavelength, effectively simplifying the sample to a homogeneous substance. Hence, further improvement of the FO-SPR signal analysis was possible by looking at the complete FO-SPR light spectrum. Therefor, a new FO-SPR model was developed in subsequent research to facilitate this full-spectrum analysis allowing for the extraction of more information about samples detected by FO-SPR sensors. This was practically demonstrated through the simultaneous and real-time determination of MOF thickness and RI during the MOF's deposition on the FO-SPR sensor. Nonetheless, upon further scrutiny of these findings and the FO-SPR model, it became evident that a more substantial improvement was possible through a fundamental overhaul to simulate a back-reflecting FO-SPR sensor more precisely. Addressing the model's limitation to meridional rays, a successive investigation introduced a generalized FO-SPR model implementing three-dimensional polarization ray-tracing calculus to accommodate skew rays. Despite its inability to fully replicate experimental FO-SPR light, the inclusion of skew rays in the generalized FO-SPR model has already rendered it a more versatile and valuable predictive and analytic tool for developing these FO-SPR sensors compared to the current model. Altogether, novel MOF functionalized FO-SPR sensors were successfully developed for selective and sensitive VOC detection, accompanied by an advanced FO-SPR model to enhance capabilities of these sensors.