Synthesis And Application Of Novel Silver Nanoclusters

Fluorimetry has outstanding advantages in sensitivity, selectivity, real-time, in situ, and so on. Recent advances in nanotechnology have given rise to a new class of fluorescent labels, fluorescent metal nanoclusters. Metal nanoclusters, silver nanoclusters ?AgNCs? in particular, have a wide range of potential applications in the life sciences. AgNCs offer several features that make them attractive for use in bioassays, including large Stokes shifts, low toxicity, water-solubility, ultrasmall size, good biocompatibility and ease of bioconjugation. Consequently, they are expected to complement or possibly even replace conventional fluorescent probes and offer great opportunities for advancing fields such as biosensors, molecular imaging optoelectronics and nanomedicine. Although researchers have developed various approaches to synthesize water-soluble fluorescent AgNCs, great effort must be exerted to improve their photostability and quantum yields ?QY?. Thus, further advances in design and synthesis of high QY and stability AgNCs remain the challenging in scientific field.Heavy metal pollution, caused by heavy metal or other compounds entering the environment, is one of the most serious environmental problems, which undermines global sustainability. Thrombin plays an essential role in blood solidification and wound cicatrization and participates in atherosclerotic disease development. It is essential to investigate thrombin activity and its inhibitory mechanism for the biochemical research and diagnosis of thrombin-related diseases. Therefore, it is of great significance to establish the rapid and sensitive method for detecting heavy metal ions and thrombin activity. This thesis composed by three aspects as follows:In chapter one, the synthesis approaches and optical properties of AgNCs was firstly summarized and the applications of AgNCs in the detection of heavy metal ions, biological molecules and biological imaging were introduced. Secondly, the pollution and harm of heavy metals to the environment and human body are described, as well as the selectivity and sensitivity of the established fluorescence techniques to heavy metal are surveyed. Finally, the important role of protease especially thrombin in the life process and the advantages and disadvantages of current fluorescence methods for detection of protease activity was discussed.In chapter two, the synthesis and application of BSA and DNA-stable AgNCs were explored. The synergy of BSA and DNA was used as templates to synthesis BSA-DNA-AgNCs. It has been investigated that the effects of different conditions on the fluorescence intensity of BSA-DNA-AgNCs. In comparision to the flourescent intensity and stability of DNA-AgNCs, the results proved that we successfully prepared new silver nanoclusters with high fluorescent intensity, long stability and good anti-oxidant capacity. Then the possible formation mechanism of BSA-DNA-AgNCs was analyzed by means of MOLDI-TOF Mass and X-ray Photoelectron Spectroscopy ?XPS?, respectively. A rapid, selective, and ultrasensitive fluorimetry has thereby been developed using BSA-DNA-AgNCs as fluorescent probes toward the detections of Hg²⁺ and Cu²⁺ ions in solution. The interactions and sensing of BSA-DNA-AgNCs with Hg²⁺ and Cu²⁺ ions were systematically characterized by Transmission Electron Microscope ?TEM?, UV-vis and fluorescence measurements.In chapter three, a label-free fluorescent method to assay thrombin activity on the basis of a designed peptide probe with a thrombin-cleavable peptide sequence and a cysteine terminus has been developed. The peptide probe can be conjugated to DNA-templated silver nanoclusters ?DNA-AgNCs? through Ag-S bonding; as a result, the fluorescence of DNA-AgNCs was enhanced. As the DNA-AgNCs-peptide conjugate was adsorbed to graphene oxide ?GO?, the enhanced fluorescence of DNA-AgNCs was quenched. Once the peptide probe was cleaved by thrombin, the resulting release of the DNA-AgNCs from the surface of GO restored the enhanced fluorescence. Thrombin can be determined with a linear range of 0-0.05 ?M with a detection limit of 1 nM. By simply changing substrate peptide sequences, the thrombin-sensitive probe with a cysteine terminus may be developed into probes to detect other proteases and kinase.