Yuhui Jin

Date of Award

7-15-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Julia Xiaojun Zhao

Abstract

In this dissertation, fluorescent silica nanoparticles (NPs) have been successfully developed to improve the performance of bioanalysis. In the first step, the sizes of silica NPs were precisely controlled by changing the organic solvent in the reverse microemulsion method. The size of the NPs can be continuously tuned from 20 to 100 nm. Then, multicolored fluorescent silica NPs were developed with controllable fluorescence properties by manipulating the properties of the dopants. To this end, both the excitation and emission spectra of the dopants could be tuned by conjugating multiple fluorophores through either avidin-biotin linkage or polylysine. With desirable sizes and fluorescence properties, these fluorescent silica NPs are prominent in fluorescence bioanalysis. Next, the multicolored fluorescent silica NPs were functionalized with target-directing groups such as antibodies. These functionalized NPs could identify the corresponding antigens such as pathogenic bacterial cells. Using these NPs as fluorescent probes in bioanalysis, the time required for bacterial detection was dramatically reduced. Moreover, when multicolored fluorescent silica NPs were applied to a bioanalysis, multiple pathogenic bacterial cells (Pseudomonas aeruginosa, Klebsiella pneumonia and Staphylococcus aureus) were identified simultaneously under a confocal fluorescence microscope. These experiments clearly demonstrate the feasibility and practicality of fluorescent silica NPs in bioanalysis. Finally, the toxicities of fluorescent silica NPs were evaluated using a series of bioassays. After cells were treated with silica NPs for two to three days, the DNA damage was examined by using the Comet Assay and measuring the activity of DNA repair protein, hOgg1. Cytotoxicity was also studied using a cell proliferation assay (MTT). Results showed that the fluorescent silica NPs did not induce genotoxicity or cytotoxicity to cells when these NPs were used at a low concentration. The toxicities of fluorescent silica NPs were also influenced by their properties, such as the dimensions and the types of fluorescent dopants. When a fluorescent photosensitizer, Rubpy, was encapsulated in the silica matrix, these fluorescent silica NPs became phototoxic. Cells, treated with these NPs under irradiation for 6 h, showed a significant decrease in their cell proliferation rate. Apoptosis was the major pathway through which the NPs caused cell death. These toxicity studies showed that fluorescent silica NPs can be safely employed in the in vitro and in vivo fluorescence bioanalysis.

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