Development of in-fiber measurement methods for the analysis of chemical components and reactions

Optical fibers have been developed as a tool for data transmission. Their ability to transport light over long distances with minimal loss is important for this. On-going advancements in this technology have enabled the production of optical fibers with capillaries that extend along the longitudinal axis through the entire fiber. These capillaries are typically filled with air, but can also be filled with other gases or even liquids. The fluids within the optical fiber can hereby interact with the light propagating through the capillaries. Because the light can be guided over a very long distance in the very narrow core of the fiber, a fluid-filled fiber represents an ideal platform for any type of light-fluid interaction. The focus of this work is on investigating various chemical systems within an optical fiber and developing fiber-based measurement methods. Three different systems were investigated for this purpose. First, an acid-catalyzed esterification was observed using Raman spectroscopy. For this, the components involved were initially measured as pure substances, and their Raman spectra were analyzed for possible differences. Based on these differences, a calibration curve was created, which was then used to observe the conversion curve of an actual reaction. Subsequently, temperature and concentration variations were performed to determine the reaction parameters. Good agreement with the values reported in the literature was observed. Secondly, a system exhibiting chemical chirality was chosen. These systems have the property that they influence the polarization of light differently depending on the ratio of the two enantiomers to each other. For this purpose, mixtures of 2-butanol with varying enantiomeric excesses were measured. Since a clearly visible influence on the polarization was observed, the pure 2-butanol was diluted and measured at lower concentrations. Limonene and mandelic acid were measured the same way. In all three cases, the dependence of the polarization on the enantiomeric excess could be clearly identified and measured. Based on this, an enzymatically catalyzed racemization of mandelic acid was then investigated. A clearly visible reaction curve was observed. Finally, the synthesis of gold nanoparticles was investigated. These nanoparticles exhibit absorption in the visible spectrum due to plasmon resonance. This absorption can be detected and measured using absorption spectrometry. The synthesis itself was carried out by reducing potassium tetrachloroaurate using polysorbate 80 as both stabilizer and reducing agent. Since a broad light source in the wavelength range of 450 to 550 nm was not available, a measurement was performed at a single wavelength of 532 nm and compared with a laser at 800 nm, for which no change was expected. As expected, a visible reduction in the transmission of the 532 nm light compared to the 800 nm light was observed, indicating the formation of nanoparticles.