The focus of this research is on the optical measurement of uranyl in a solid matrix using fluorescence spectroscopy. Nanoporous silica-based materials were used to extract uranyl from contaminated soil and to enhance the fluorescence intensity and lifetime. The fluorescence lifetime and intensity of uranyl ions adsorbed on porous silica-based materials of varying pore size was measured as a function of pH and in the presence of fluoride. The feasibility of uranyl fluorescence detection on the top of soil by silica gel is carried out by four types of natural soil. The results show that the uranyl fluorescence intensity can be enhanced by approximately two orders of magnitude by the silica nanoporous matrix from pH 4-12 with the greatest enhancement occurring from pH 4-7. The enhanced fluorescence lifetime can be used in time-gated measurements to help minimize the influence of background environmental fluorophores. The pH and the fluoride variation causes different uranyl speciation and results in a peak shift in the fluorescence spectrum. The mechanism of the uranyl ion on the silica nanoporous matrix was studied through 15 different silica materials with different water content ratios and various concentrations of uranium on different silica structures. The result shows that the particle size, pore size, water content and uranyl concentration on silica surfaces are all important factors for optimizing the fluorescence intensity. The spacing between silica materials, either the pore inside materials or the space between particles, causes the variety of uranyl distribution on the material surface and changes the fluorescence performance. Also, X-Ray Photoelectron Spectroscopy (XPS) is used to identify the possible uranyl surface species on silica. The fluorescence emission spectra from silica materials and the XPS results are consistent with the presence of two different uranyl compounds. The specific surface area of silica materials plays an important role on uranyl adsorption mechanism. To further enhance the sensitivity, an optical ball lens was used to preferentially direct the fluorescence signal toward the excitation source in standoff measurements. The application of the ball lens was found to increase the detection distance up to 14 times.

Die Aufgabe des Proteins Arrestin ist die Beendigung der Signalweitergabe über den GPCR Signalweg. In Stäbchenzellen bindet Arrestin an Licht-aktiviertes phosphoriliertes Rhodopsin um die Signalweitergabe zu unterdrücken. Die Bindung von Arrestin an Rhodopsin erfolgt in zwei Schritten. Zunächst wechselwirkt Arrestin mit dem phosphorilierten C-Terminus von Rhodopsin und bildet einen prä-Komplex, dies induziert Konformationsänderungen im Arrestin wodurch die Bildung eines High-affinity Komplex unter Kopplung an den helikalen Kern des aktivierten Rezeptors erfolgen kann. Biochemische Untersuchungen und Kristallstrukturen haben einen Einblick in die Konformation des Komplexes aus Arrestin und Rhodopsin ermöglicht. In dieser Arbeit werden site-directed Fluorezenz Experimente angewandt um die strukturellen Änderungen zu untersuchen, die bei der Bindung von Arrestin an Rhodopsin ablaufen und der nterschiedlichen Bindungsmodi innerhalb der Wechselwirkung zwischen Arrestin und Rhodopsin. Insbesondere wird hier eine, bisher nicht beschriebene, Assoziation von Arrestin an die Membran untersucht. Des Weiteren wurden Erkenntnisse über die Struktur des prä-Komplexes gewonnen. Die Konformation vom Arrestin im prä-Komplex scheint die Konformation im Basalzustand nachzubilden unter Beteiligung zweier Kontaktstellen: Interaktion mit dem phosphorilierten C-Terminus des Rezeptors und Assoziation mit der Membran. Beim Übergang in den High-affinity Komplex durchläuft Arrestin eine Konformationsänderung in eine aktivere Konformation: der C-Terminus wird verdrängt, es erfolgt eine Neuausrichtung der zentralen flexiblen Schleifen und die Orientierung des Membranankers ändert sich. Die Aufgabe des prä-Komplexes ist somit Arrestin und den Rezeptor zusammen zu bringen sowie die korrekte Orientierung sicherzustellen um einen schnellen Übergang in den High-affinity Komplex zu ermöglichen. / The protein arrestin is responsible for termination of GPCR signalling. In the rod cell, arrestin binds light-activated phosphorylated rhodopsin in order to block further signal transduction. The binding of arrestin to rhodopsin is a two-step process. Arrestin first interacts with the phosphorylated receptor C-terminus in a pre-complex, which induces conformational changes in arrestin that allow coupling to the helical core of the active receptor in a high-affinity complex. Biochemical studies and crystal structures have provided insights into the conformation of the arrestin-rhodopsin complex. This dissertation describes site-directed fluorescence experiments, which were carried out to further investigate the conformational changes occurring upon arrestin binding to rhodopsin and the nature of different binding modes of the arrestin-rhodopsin interaction. In particular this involved characterization of a previously unidentified association of arrestin with the membrane, as well as further elucidation of the structure of the pre-complex. The conformation of arrestin in the pre-complex is indicated to resemble that of the basal state of arrestin, and involves two sites of contact: interaction with the phosphorylated receptor C-terminus, and association with the membrane. Upon transition to the high-affinity complex, arrestin undergoes a conformational change to a more active conformation: the auto-inhibitory C-tail is displaced, there is movement within the central flexible loops, and the orientation of the membrane anchor changes. The pre-complex therefore most likely functions to bring arrestin and the receptor into close contact, and in the correct orientation, to allow for fast transition to the high-affinity complex.