Synthesis Of Fluorescent Gold And Silver Nanoclusters For The Application In The Detection Of Inorganic Ions And Biomolecules

Gold and silver nanoclusters(Au/Ag NCs) with core sizes smaller than 2 nm approaching the fermi wavelength of electrons, the continuous density of states breaked up into discrete energy levels leading to possess special physicochemical properties. The researchers especially concerned their fluorescence properties,due to high quantum yield, tunable emission spectrum, good photostability and excellent biocompatibility. In view of this, Au/Ag NCs have been an attractive frontier of nanoparticle research, widely used in the environmental monitor, medical, biochemical analysis, medical analysis etc., greatly promoting the high speed development of various fields. However, the simple and environment-friendly synthesis method of Au/Ag NCs must continue to be further developed to obtain nanoclusters with particular sizes and fuction. To achieve this objective, we have systematically studied the synthesis of Au/Ag NCs as well as their applications in the detection of inorganic ions and biological molecules. These optical sensing systems have the advantages of green, simple, good specificity and high sensitivity, and the main contents of this work can be concluded as follows:1. Preparation of BSA-Au NCs and used for detection of free chlorine in tap waterEmploying bovine serum albumin(BSA) as a capping and reducing agent, soluable gold nanoclusters(BSA-Au NCs) with strong fluorescence and high stability have been successfully prepared. The study found that the free chlorine can quenched the fluorescence of BSA-Au NCs by oxidizing their gold atoms, establishing a simple and sensitive detection method. In the optimized condition, the decrease in fluorescence intensity of BSA-Au NCs allowed the sensitive detection of free chlorine in the range of 8.0×10-7~8.0×10-4 mol/L. The detection limit was 5.0×10-7 mol/L at a signal-to-noise ratio of 3. BSA-Au NCs were demonstrated as a novel fluorescence probe for sensitive and selective detection of free chlorine in drinking water. The proposed fluorescent assay for free chlorine possessed low detection limit, wide linear range and good selectivity. Real tap water samples were analyzed with satisfactory results, which suggested its potential for actual water quality analysis.2. Sensitive and selective detection of Hg2+ by fluorescent Ag nanoclusters via a N,N-dimethylformamide-directed approachA facile preparation of highly fluorescent Ag nanoclusters(Ag NCs) has been reported using a surfactant-free N,N-dimethylformamide(DMF) reduction method by reflux at 140 ℃. The as-prepared samples were characterized by UV-Vis absorbtion spectroscopy, fluorescence spectroscopy and HRTEM. The results showed that the Ag NCs with small size emited strong blue fluorescence possessing excellent water-solubility and photostability. Moreover, the fluorescence from Ag NCs can be efficiently quenched by mercury ions(Hg2+). By virtue of the specific response, a new, simple, selective and sensitive fluorescent method for detecting Hg2+ has been developed based on DMF-Ag NCs. This method showed a good linear relationship within the concentration range of 5.0×10-9~1.5×10-7 mol/L, the detection limit was 3.0×10-9 mol/L, and the correlation coefficient R2= 0.9958.3. Design and synthesis of oligonucleotide-stabilized fluorescent silver nanoclusters for detection of biotinIn this study, we have designed a biotinylated cytosine-rich sequence template for synthesis of novel fluorescent DNA-Ag NCs. Research showed that the property of the novel DNA-Ag NCs was related to the modified position of the biotin. Only when biotin was linked to the middle thymine(T) of the DNA sequences, the novel DNA-Ag NCs can emit the strongest fluorescence intensity. Moreover, the stability of the DNA-Ag NCs can be effectively affected by avidin through biotin-avidin binding, causing the fluorescence of the DNA-Ag NCs to be quenched. While, if the free biotin was further introduced to this system leading to the restoration of the fluorescence by competition, thus achieving detection of biotin. Under optimum conditions, the fluorescence recovery is linearly proportional to the concentration of biotin between 1.0×10-8 mol/L and 1.0×10-6 mol/L and the detection limit is as low as 6.8×10-9 mol/L. This novel DNA-Ag NCs with excellent fluorescent properties and convenient post-modification has been proven to further facilitate biosensing and bioimaging applications.