The Synthesis Of Gold Nanoclusters And Its Application In Intracellular Thiols Imaging

Gold nanoparticles show unique optical and electronic properties due to their interfacial effect, quantum effect, high specific surface area and small-size effect scale, which are different from those of traditional bulk materials. Thus they have attracted tremendous interest and become hot research focus. When the size of gold nanoparticles is decreased to its Fermi-wavelength, its electronic structure is similar to that of semiconductor andsesulting the discontinuous energy level can arouse fluorescence of the nano-cluster. Compared to traditional fluorescent probes, nano-clusters have more advantages including higher quantum yields, longer fluorescent lifetime, stronger anti-photobleaching ability, size-dependent emission wavelength, larger Stokes shifts and lower cytotoxicity. Therefore, gold nano-clusters are promising nanomaterials, with wide use in biolabeling and fluorescence imaging fields.In this dissertation, fluorescence gold nano-clusters were prepared under different conditions, in which chloroauric acid was used as a precursor and GSH was used as a reducer Further researches focused on the influence of thiols to the fluorescence of gold nano-cluster. A variety of analysis measures which contain transmission electronic microscopy (TEM), mass spectroscopy (MS), X-ray photonelectronic spectra (XPS), fluorescence spectra, infrared and UV-vis spectra are used to characterize the morphology, structures, properties of as-prepared materials and explore the formation mechanism. Also the application of gold nano-cluster in tumor cell imaging was inspected. The main researches are as below:1. The influence on the preparation of Au nanoclusters by different conditions, including the molar ratio of the reaction precursors, the reaction time, and the heating temperatures. The results showed that the stable low fluorescent gold nano-clusters(AuGSH(low)) can be obtained at a molar ratio of AuCl4:GSH=5mM:5mM and 80℃ in 2 hours. This is a simple, efficient, and low-cost method. The excitation and emission wavelength are 450nm and 570nm respectively.2. The properties of gold nano-clusters, including their fluorescence properties, toxicity, reaction with thiols, and tumor cell imaging, were studied. The results showed that when AuGSH(low) was added to thiol compounds, the fluorescence was significantly enhanced due to generation of high fluorescent gold nanoclusters, AuGSH (high), illustrating that AuGSH(low) can specificly reacted with thiols. MTT assays illustrated the cytotoxicity of AuGSH(low) is very low. The confocal imaging results demonstrate that intracellular thiols, especially GSH can specifically binding to AuGSH(low) and enhance the fluorescence, achieving fluorescent thiols imaging.3. The AuGSH-FA was prepared by AuGSH(low) modified with activated folic acid(FA). The MTT research show that AuGSH-FA is noncytotoxic. The confocal imaging results verify that AuGSH-FA can be internalized to folate receptors over-expressed HeLa cells more quickly, allowing the decrease of imaging time from4 hours to 1 hour. Thus it indicated the AuGSH(low) modified with FA can shorten the imaging time effectively.