The Microwave Assisted Preparation Of Gold Nanoclusters And The Application In Hg²⁺ Detection

Gold nanoclusters is composed of a few to roughly a hundred metal atoms with diameters normally below 3 nm.Compared with other optical probes,gold nanoclusters exhibit unqie optical properties,low toxicity,good water solubility and good biocompatibility.Therefore,this new type of fluorescent probe has attraceted much research interest.In this thesis,we have prepared a new type of water-soluble Au NCs using folic acid as template by microwave assisted method.It was then used as a fluorescent probe for the rapid and sensitive dectection of mecury ion.The specific contents are as follows:In chapter 1,we briefly review the properties,preparation methods of gold nanoclusters and their applications in sensing and cell imaging.In chapter 2,the folic acid decorated AuNCs(FA-Au NCs)are prepared and characterized.FA-Au NCs were prepared by microwave heating for 90 s,with chloroauric acid as precursor,folic acid as ligand and sodium borohydride as reducing agent,followed by the purification with G-25 Sephadex gel.The absolute quantum yield of FA-Au NCs was 27.2%.The gold nanoclusters were characterized by Fourier transform infrared spectroscopy(FT-IR)and Zeta potential analyzer,confirming that folic acid and gold nanoclusters are successfully bonded by Au-N covalent bond,and the surface of FA-Au NCs is negatively charged.Transmission electron microscopy(TEM)results showed that the prepared FA-Au NCs was well dispersed with a regular spherical shape and a particle size of 2.45 nm.X ray photoelectron spectroscopy(XPS)results indicated that FA-Au NCs contain four elements:gold,carbon,nitrogen and oxygen,and Au+ and Au0 exist simultaneously in gold nanoclusters.In chapter 3,the fluorescence(FL)properties of the FA-Au NCs were investigated detailedly and applied in the sensing of Hg2+.The prepared FA-Au NCs exhibit excitation-independent FL behavior in a certain range,with a decrease in the fluorescence intensity as the excitation wavelength increases.The excitation/emission maximum is 280 nm/445 nm,respectively.The fluorescence intensity of FA-Au NCs remains stable within the pH range of 3-12,and an ionic strength up to 0.3 mol L-1 NaCl and irritating time of 2 h hardly pose any effect on the FL of FA-Au NCs.Based on the quenching effect of Hg2+ on the fluorescence of the FA-Au NCs,a sensitive and fast sensing approach for the measurement of Hg2+ was developed,with a LOD of 37 nmol L-1 and a linear range of 0.1-5 μmol L-1.The fluorescent probe was successfully applied in the analysis of Hg2+ in the lake water and snow water,demonstrating the feasibility of this approach.