Synthesis Of Silver And Copper Nanoclusters For Biochemical Analysis

Metal nanoclusters is a typical nanomaterial with unique chemical, physical and electrical properties, which has got great attention due to their ultra-small size, high fluorescence quantum yield, low toxicity, high optical stability, good water solubility and biocompatibility. At present, a lot of work has focused on the synthesis and applications of metal nanoclusters. In this thesis, on the basis of the synthesis of silver and copper nanoclusters with high fluorescence intensity, we use silver and copper nanoclusters as fluorescent probe to detect DNA associated with the disease and metal ion associated with environmental pollution, which has important theoretical and practical research value. This thesis mainly includes two aspects of work:(1) We proposed an exonuclease III-assisted recycling amplification(ERA) coupled with fluorescent DNA-scaffolded silver nanoclusters(Ag NCs) method for detecting hepatitis B virus(HBV) DNA with high sensitivity. Two different molecular beacons(MBs) were employed in the sensing platform, MB1 and MB2. In the absence of targets, the MBs self-hybridize into stable stem-loop structures with exonuclease III(Exo III) cleaving resistance, and the MB2 contains a C-rich loop which can be utilized to synthesize high fluorescence AgNCs. However, in the presence of targets, the targets can bind with MB1 forming partly duplex structure. With the cleaving of Exo III, the target DNA can be liberated and initiate the cycle of MB1-target hybridization, while the generated trigger DNA can hybridize with MB2, inducing a conformational change of MB2 from hairpin to single-stranded structure, this structural change of MB2 would influence the formation of Ag NCs, thus producing weak fluorescence signal. Besides, the released trigger DNA could activate the cycle of MB2-trigger hybridization. This proposed method for HBV DNA analysis exhibits a detection limit of 0.97 nmol/L with high specificity, and demonstrates its applicability for the HBVdetection in human serum.(2) We developed a simple and environmental friendly approach to synthesize hyperbranched polyethyleneimine-protected copper nanoclusters(hPEI-CuNCs) with great stability against extreme pH, high ionic strength, thiols etching and light illumination, which are then conjugated to the surface of silica coated CdSe quantum dots(QDs) to design a ratiometric fluorescence probe. In the presence of different amounts of Cu2+, the fluorescence of CuNCs can be drastically quenched, while the emission from QDs stays constant to serve as a reference signal and the color of the probe changes from yellow-green to red, resulting in ratiometric and visualization detection of Cu2+ with high accuracy. The detection limit for Cu2+ is estimated to be 8.9 nmol/L, much lower than the allowable level of Cu2+(～20 μmol/L) in drinking water set by U.S. Environmental Protection Agency. Additionally, this probe can be also applied for the determination of Cu2+ in real water samples.