Synthesis Of Water-Soluble Silver Nanoclusters And Their Fluorescence Sensing Applications

Noble metal nanoclusters are the relatively stable molecular-level atom aggregates which consist of tens to hundreds of metal atoms,and have the size close to the Fermi wavelength of electrons.It bridges the gap between the metal atoms and nanoparticles,and exhibits the molecule-like chemical and optical properties.Water-soluble silver nanoclusters show the advantages of ultra-small size,low toxicity,excellent light stability,large Stokes shift,good biocompatibility,simple green synthesis method and good antibacterial properties,which have made the nanoclusters widely used as fluorescent probes.In this paper,a variety of different water-soluble silver nanoclusters were synthesized by hydrothermal reduction,photo reduction,chemical reduction and other methods.Two completely different fluorescence sensing systems was constructed based on these fluorescent silver nanoclusters as fluorescent probes,and these sensing systems were separately used in the analysis of cysteine and the identification of heavy metal ions.The main research contents are as follows:?1?Glutathione-protected silver nanoclusters used as the fluorescence-enhanced probe for the detection of cysteineGlutathione-protected silver nanoclusters?GSH-Ag NCs?synthesized by boiling water method have weak but stable red luminescence.When cysteine?Cys?was added in the system,Cys could anchor on the metal core of Ag NCs through Ag-S bond,a new kind of Ag NCs co-protected by glutathione and cysteine was formed.The fluorescence of Ag NCs could be significantly enhanced because of the increase in the number of ligands.GSH-Ag NCs could be applied as a fluorescence-enhanced probe for analyzing cysteine.The detection system can quantitatively analyze Cys at the concentration of 2–3000?M with a detection limit of 0.51?M.When detecting the cysteine contents in fetal bovine serum samples,the recovery rate was found between95.07-101.38%,indicating that this method had the possibility of detecting Cys in actual samples.This work not only reported a method for the turn-on detection of cysteine but also provided a new strategy for the synthesis of dual ligand-protected Ag nanoclusters.?2?A fluorescence sensing arrays based on 4 kind of polymers templated silver nanoclusters for the identification of 7 heavy metal ionsFour kinds of silver nanoclusters templated by different polymers were synthesized through photo reduction method and chemical reduction method.The rich free carboxyl and amino groups of polymers ensure the efficient reaction between the nanoclusters and heavy metal ions.A fluorescence sensor array was constructed by using these silver nanoclusters as sensing elements and this sensor array can be used to recognize 7 kinds of metal ions including Pb²⁺,Fe³⁺,Cu²⁺,Cd²⁺,Cr³⁺,Co²⁺and Ni²⁺.The fluorescence intensity ratio of Ag NCs before and after adding metal ions were used as the output signals and principal component analysis?PCA?was applied to reduce the dimensionality of the data.A PCA scatter gram that clearly distinguished the seven metal ions could be obtained.This sensor array exhibited a good performance when the pH was 7 and the ion concentration was in the range of 15-800?M.The sensor array could also clearly distinguish these heavy metal ions and identify unknown metal ions in the tap water,which further indicated that the fluorescent sensor array had the possibility of practical application.