Date of Award

Winter 2023

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

First Advisor

Rudi RS Seitz

Second Advisor

Marc MAB Boudreau

Third Advisor

Christopher CFB Bauer

Abstract

This thesis describes a series of optical chemosensors based on FRET between fluorophores on the polymer and the substrate. It involved the preparation of the polymer and nanoparticles for the chemosensor, and the sensing behavior based on the preparation methods.A photophysically inert sensor matrix was prepared by a robust and simple emulsion method. Stannic oxide encapsulated silica nanoparticles with diameters between 25 and 70 nm have been prepared by one-pot reverse-phase emulsion methodology. The constituents and core/shell morphology of the nanoparticles were demonstrated by electron microscopic technology, energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) was employed as an assisted technology to provide additional constitutional and structural information. It has been shown that nanoparticles prepared by this method are optically clear in suspension. After anchoring optical indicators, this nanoparticle can be utilized as a sensor module both in biology and other analytical areas. Encapsulated stannic oxide increases the density of the particles making them easier to recover by centrifugation. The first sensing system is a novel copper(II) ion indicator based on polymer conformational change. This polymer sensor has two different fluorophores on either end. If one of them is a fluorescent donor and the other is a fluorescent acceptor, then the extent of Foerster resonance energy transfer (FRET) will depend on polymer conformation. The sensitivity for these sensors is tunable based on the chain length and the amount of the receptor on the polymer. This is revealed by the fluorescence response of 30mer, 50mer, and 100mer of poly(N-isopropyl)acrylamide with different amounts of the metal chelation monomers. The fluorescent signal can maintain stable after the mental binding. The photoluminescence results agree with the length calculation of polyelectrolytes. A fluorescent standard curve was created for the measurement of different concentrations of copper ions. The sensing limit can reach 10-10 M analyte, which is suitable for the measurement of chemicals in trace amounts in the environment. The sensitivity can be increased by using a ligand with higher affinity for Cu(II). The second sensor is a ratiometric fluorescent indicator for histidine fabricated using the molecular imprint technique with predominantly noncovalent crosslinks. The polymer was attached to the surface of a silica-covered stannic oxide nanoparticle. The sensing mechanism is based on the polymer conformational change-induced energy transfer between the two fluorescent groups on the surface of the nanoparticle and the end of the polymer chain. The rebinding of the analyte on the templated polymer will result in a conformational change of the well-tailored polymer chain. The polymer shell on the surface of the nanoparticles is proved by the TEM image. The sensing ability of the nanoparticles is tested by equilibrium dialysis and the detection limit can reach nearly 10-6 M of the analyte. The proper chain length of the polymer and pH was tuned for best performance. The selectivity of the nanoparticle sensor was evaluated at neutral pH. Through further development, this imprinted polymer nanoparticle can be utilized for various analyte detection.

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