Studies On Synthesis Of Biomolecule Stabilized Fluorescent Noble Metal Nanoclusters And Their Analytical Applications

Noble metal nanoclusters (NMNCs) are new kinds of fluorescent materials developed in recent years. Due to their excellent fluorescence properties, unique chemical properties and good biocompatibility, NMNCs have been well studied and favored by scientists in wide fields. Currently, the research of NMNCs mainly focused on two fields:On the one hand, the synthesis of NMNCs with excellent fluorescence property by exploring template molecules or a synthetic route. The other is study on NMNCs’ optical properties and their application in biochemical analysis, biological imaging and other fields. In this thesis, effects of rich G-base mismatch degree, package degree and the light radiation on the fluorescence of G-bases enhanced DNA/Ag nanoclusters were studied intensively, and then, We have developed a series of DNA/Ag nanoclusters as fluorescent probes for detection of metal cations, cyanide ion, ascorbic acid and pathogenic DNA sequences. The thesis also developed a rapid photo-synthesis method for preparing of bovine serum albumin templated gold nanocluster (BSA/AuNCs) with tunable fluorescence emission, and the prepared BSA/AuNCs were used as fluorescent probes to detect silver ions and image biological tissues. The mainly studies are as follows:1. A kind of novel G-rich enhanced double-stranded DNA/Ag nanoclusters was synthesized and a highly sensitive fluorescence spectroscopy method for detection of Hg2+and Cu2+was established based on the fluorescence quench phenomenon of DNA/Ag nanoclusters by Hg2+and Cu2+. Compared with the single-stranded DNA/Ag nanoclusters, double-stranded DNA/Ag nanoclusters have stronger and more stable fluorescence. And thus, double-stranded G-rich enhanced DNA/Ag nanoclusters were used to detect Hg2+and Cu2+with higher sensitivity than single-stranded DNA/Ag nanoclusters. By using a masking agent EDTA, selective detection of Hg2+was achieved in the presence of Cu2+and other metal ions. Hg2+and Cu2+in natural water samples could also be detected using this method.2. A single-base-mismatched G-rich duplex DNA/Ag nanoclusters was synthesized and applied to detect cyanide ions. By changing mismatch degree of G-rich hybridization sequence, the effects of rich G-base and DNA/Ag nanoclusters hybridization conditions on DNA/Ag nanocluster fluorescence intensity was studied. The results indicated that fully complementary G-rich double-stranded DNA/Ag nanoclusters have lower fluorescence than single-base mismatched double-stranded G-rich DNA/Ag nanoclusters. The study also found that the fluorescence of a single-base mismatched double-stranded G-rich DNA/Ag nanoclusters can be quenched easily by cyanide ion. A fluorescence spectrometry for quantitative detection of cyanide ions was established with good selectivity and a detection limit as low as24.6nM has been achieved.3. A fluorescence analysis method for selective recognition of ascorbic acid by double-stranded DNA/Ag nanoclusters was developed. The strategy based on the different packet degrees of G-rich nucleotide sequence to DNA/Ag nanoclusters would affect the fluorescence properties of double-stranded G-rich DNA/Ag nanoclusters. The interaction between biological small molecules and different package degree of G-rich double-stranded DNA/Ag nanoclusters was also studied. The results showed that the fluorescence of G-rich double-stranded DNA/Ag nanoclusters with one end not hybridized completely can quenched by small biological molecules, such as ascorbic acid, dopamine and cysteine. However, if both ends of DNA/Ag nanoclusters were hybridized and packaged, the fluorescence can not be quenched by ascorbic acid excepting dopamine and cysteine. And thus, selective recognition of ascorbic acid can be realized by G-rich double-stranded DNA/Ag nanoclusters with different end.4. A G base-enhanced dsDNA/Ag nanoclusters with a probe sequence complementary to pathogenic DNA sequence has been designed. In the presence of the target DNA, the probe sequence in dsDNA/Ag NCs would hybridize with target DNA and release G base sequence from dsDNA/AgNCs. Thus, the fluorescence of dsDNA/Ag NCs would decrease with the increasing of the target DNA. Based on this phenomenon, we established an analytical methods for pathogenic DNA sequence on the basis of double-stranded G-rich DNA/Ag nanoclusters.5. The effects of the light radiation on the fluorescence properties of DNA/Ag nanoclusters were studied. The fluorescence fluctuation of single-stranded DNA/Ag nanoclusters (ssDNA/Ag NCs) and G-rich enhanced double-stranded DNA/Ag nanoclusters (dsDNA/Ag NCs) were studied by light illumination with different wavelength. The results showed that the fluorescence of ssDNA/Ag NCs will be drastically reduced under irradiation of light at wavelength from ultraviolet to near-infrared. However, the fluorescence of dsDNA/Ag NCs would be quenched under light illumination of lower wavelength and enhanced under light illumination of longer wavelength. This phenomenon allows us to "turn on" or "turn off’ dsDNA/Ag NCs fluorescence by controlling an incident light. And also, we believe that these studies and the findings would help researchers to further understand the fluorescent DNA/Ag nanoclusters.6. A rapid photo-catalytic method for synthesis of fluorescent BSA/Au nanoclusters has been developed. By selecting appropriate wavelength of light illumination and photo-catalytic agent, we significantly shortened the synthesis time of BSA/Au nanocluster compared with ordinary synthesis rate. We also found that fluorescence emission wavelength of the prepared BSA/Au NCs would shift to longer wavelength only in the presence of Ag+. Thus, we established a method for rapid, selective and visual detection of Ag+ions by using BSA/Au nanoclusters as a sensing probe.7. A series of BSA/Au NCs with fluorescence emission ranging from560to630nm were rapidly synthesized by adjusting the concentration of Ag+in a photo-catalytic route. The fluorescence properties, composition, cellular toxicity, biocompatibility and stability of the prepared BSA/Au NCs were studied by relative experiments. Finally, the BSA/Au nanoclusters were successfully used in vivo fluorescence imaging of nematodes.