Preparation And Application Of New Multi-size Fluorescent Silver Nanoclusters

With the advantages of ultra-small size,low toxicity and good fluorescence stability,silver nanoclusters are widely used in the fields of biomarker,biological imaging,biosensor and biomedicine.The innovation of this paper is to use different mercaptan molecules as the ligands of silver nanoclusters.Through different experimental schemes,we synthesized multi-size fluorescent silver nanoclusters protected by different ligands.In addition,a variety of testing methods were used to characterize and analyze the morphology,composition and fluorescence properties of silver nanoclusters.In this paper,we mainly studied the synthesis and characterization,fluorescence properties,biological imaging and heavy metal detection of multi-size silver nanoclusters protected by different ligands.The main contents and conclusions of this thesis are as follows:1.Preparation and application of glutathione-protected multi-size fluorescent silver nanoclusters.(1)Glutathione(GSH)was used as the ligand for the synthesis of silver nanoclusters.GSH AgNCS(?)were prepared by a simple one pot method with the molar ratio of AgNO₃:GSH:NaBH₄=1:3:10.It is proved that it is a pure single-size cluster by UV combined with PAGE analysis.It was observed by TEM that its morphology was spherical and the average particle size was 1.71nm.Through TG analysis,it is inferred that its approximate molecular formula is Ag_2.42x(SG)_x.The formation mechanism of clusters was also studied by FT-IR.The results show that during the formation of clusters,GSH molecules and Agatoms will bind to the surface of Agin the form of Ag-S bond.Moreover,the prepared GSH-AgNCs(?)has good fluorescence properties,such as large Stocks shift(198nm),fluorescence quantum yield of?4.95%,good fluorescence stability(fluorescence intensity decreased by 50.1%in aqueous solution for 24 hours)and strong salt tolerance(fluorescence intensity decreased by27.8%in 9.0 g/L NaCl solution).We tried its imaging in human embryonic kidney cells(Hek293)and hepatocellular carcinoma cells(Hepg2).The results show that it can partially enter these two kinds of cells,and it also has very low biotoxicity.Even in the presence of high concentrations of 200 ug/ml GSH-AgNCs(?)clusters,the survival rates of Hek293 and Hepg2 cells are still 81.9%and 93.1%.(2)By adjusting the reaction conditions,pure single size GSH AgNCS(?)silver nanoclusters were obtained under the condition of AgNO₃:GSH:NaBH₄=1:4:20.Its morphology is also spherical,the average particle size is 1.34nm,and the molecular formula is Ag_1.98y(SG)_y.Moreover,GSH-AgNCs(?)has excellent fluorescence properties such as large Stocks shift(230nm),high fluorescence quantum yield(?7.19%),good fluorescence stability(fluorescence intensity decreased by 60.3%in aqueous solution for 24hours)and strong salt tolerance(fluorescence intensity decreased by 36.1%in 9.0 g/L NaCl solution).Moreover,it also has very low biotoxicity when high concentration 200 ug/ml GSH-AgNCs(?)clusters exist.The survival rates of Hek293 and Hepg2 cells were still89.3%and 92.6%.2.Preparation and application of fluorescent silver nanoclusters protected by N-acetyl-L-cysteine(1)Firstly,N-acetyl-L-cysteine(NALC)was used as the ligand for the synthesis of silver nanoclusters.By changing the experimental method and adjusting the reaction conditions,pure and single size NALC-AgNCs were obtained after rapid reaction and purification at the molar ratio of AgNO₃:NALC:NaBH₄=1:2:20.Its TEM morphology is spherical,the average particle size is 1.54nm,and we also use TG to analyze the composition of NALC-AgNCs,and infer that its approximate molecular formula is Ag_2.4x(NALC)_x.In addition,NALC-AgNCs has a large Stocks shift(205nm),good fluorescence stability(33.1%decrease in fluorescence intensity after aging in aqueous solution)and good salt tolerance(29.1%decrease in 9.0 g/L NaCl solution).Based on the good fluorescence properties of NALC-AgNCs,on the one hand,it can be used for the highly selective and sensitive detection of heavy metal lead ions,on the other hand,it has also been successfully applied to the imaging of liver cancer cells(Hepg2).(2)In addition,by changing the molar ratio of AgNO₃ and NALC to 1:1,1:1.5,1:3,1:4,we synthesized multi size silver nanoclusters mixture system,and three single size silver nanoclusters(NC1,NC2 and NC3 in order of size)were obtained after purification.We also compared the fluorescence properties of NC1,NC2,NC3 and their mixture silver nanoclusters(mix).The results show that with the decrease of the size of three pure silver nanoclusters(NC1>NC2>NC3),the fluorescence emission peaks of NC1,NC2,NC3 are blue shifted,and the fluorescence intensity of NC1,NC2,NC3 decreases gradually,while the fluorescence intensity of mix is in the middle position,This may be because the size of mix is in the middle of the three pure silver clusters,so the fluorescence intensity will be affected by the superposition effect of the three pure silver clusters.