Synthesis,Structure And Properties Of High Quantum Yield Gold Nanoclusters And Their Fluorescence Imaging Application

Fluorescent gold nanoclusters（Au NCs）have the advantages of small size,good photoluminescence performance,good stability,large Stokes shift,low cytotoxicity,and good biocompatibility and application prospects in biomedical fields such as biosensing,bioimaging,photothermal therapy,and antimicrobial.However,compared with quantum dots or organic dyes,the fluorescence quantum yields of most Au NCs are still not competitive.In this thesis,high quantum yield gold nanoclusters（His-Au NCs）were synthesized using histidine as ligand.A systematic study on the formation process of gold nanoclusters and mechanism of strong fluorescence was conducted.The main research includes:1.A new method for the synthesis of strong fluorescence His-Au NCs using histidine as a ligand in boiling water is proposed.By varying the reaction temperature,it was found that His-Au NCs obtained under boiling water condition exhibited excellent optical properties with fluorescence quantum yield as high as 86.21%.Characterization and analysis were carried out using UV-vis absorption spectroscopy,fluorescence spectroscopy,infrared spectroscopy,transmission electron microscopy,etc.The results show that His-Au NCs were spherical and well dispersed,with an average particle size of 1.86 nm,and emitted blue fluorescence(λ_em=430 nm).His-Au NCs showed good stability under 30 min UV illumination,50℃high temperature,800μM Na Cl ionic strength,and 15 days storage time.2.The growth process of His-Au NCs was explained by regulating the synthesis of gold nanoclusters by changing the temperature.Two types of His-Au NCs with different fluorescence properties were obtained,and the source of the high quantum yield of synthesized His-Au NCs was explored by comparing their components.The high quantum yield of His-Au NCs originates from ligand-metal-metal charge transfer（LMMCT）,indicating that the charge transfer leaps from the carbonyl oxygen on the carboxyl group of ligand on the cluster surface to monovalent Au ions and then to Au nuclei.By systematically investigating the functional groups of histidine ligands,it is found that the imidazole group plays a reducing role in the synthesis of His-Au NCs,the side-chain amino group is essential for the fluorescence generation of His-Au NCs,and the carboxyl group is the key factor for the high fluorescence quantum yield.3.His-Au NCs exhibited sensitive and selective fluorescence response to ROS,and Cl O^-showed a good linear relationship with the degree of fluorescence quenching of Au NCs in the concentration range of 1-100μM,with a limit of detection of 0.36μM.With the advantages of good water-solubility and low cytotoxicity,His-Au NCs have been successfully applied to cellular ROS imaging.