Controllable Synthesis,Luminescence Tuning And Sensing Applications Of Metal Nanoclusters

In recent years,precious metal nanoclusters with luminescent properties have attracted wide attention in the scientific community.Compared to organic dyes and quantum dots,luminescent metal nanoclusters(MNCs)consist of several to dozens of metal atoms(gold,silver,copper,etc.)composition with small micro-grain size,good biocompatibility,low toxicity and its unique physical,optical and electrical properties,such outstanding advantages make it potential for suitable sensor and biomedical applications.The ideal material has become a research hotspot in the scientific research field in recent decades.Among these MNCs,especially metal nanoclusters(MNCs)with sulfhydryl small molecules as stabilizers and reducing agents,due to low biotoxicity,simple synthesis method,adjustable emission wavelength,high quantum yield and good photobleaching resistance,etc.The advantages have aroused great interest,and such potential nanomaterials are expected to play a huge role in the fields of sensing and analytical application.In this thesis,we synthesized three photoluminescent metal nanoclusters protected by mercapto small molecules as stabilizers and reductants,covering copper nanoclusters(CuNCs)protected by thiol-methoxysilane,silver clusters(AgNCs)protected by thiosalicylic acid,and gold clusters(AuNCs)protected by glutathione.Firstly,the quantum yield and oxidation resistance of copper nanoclusters(CuNCs)were improved by silica coating,and that Hydrogen sulfide was detected by disulfide exchange reaction.Secondly,silver nanoclusters(AgNCs)were guided by hydrophobicity to self-assemble into AIE particles in water for detection of heavy metal mercury ions and cell imaging.Finally,the luminescence property by multiple stimulations of gold clusters(AuNCs)was investigated,and GSH-AuNCs was a fluorescent probe for cytoplasmic imaging.(1)Copper nanoclusters have shown tremendous application perspective because of their outstanding luminescence properties,inherent biocompatibility,and easy accessibility;however,low emission brightness and poor resistance to ambient oxygen greatly limit their wide applications in long-term sensing and bioimaging.Herein,we develop an effective and general approach to enhancing the luminescence and stability of copper nanoclusters through in situ generation of a silica shell and further propose a versatile surface functionalization method to achieve functional copper nanoclusters via the formation of a second layer of a silica shell.The use of thiol-containing trialkoxysilane facilitates in situ generation of a silica shell on the surface of copper nanoclusters,and the existence of the first layer of a silica shell substantially improves the emission efficacy of copper nanoclusters.The introduction of a second layer of a silica shell not only greatly enhances the brightness and stability of copper nanoclusters but also provides versatile surface functional groups via hydrolysis and polymerization of trialkoxysilance derivatives with different functionals on the surface of a silica shell.Thiol-functionalized silica-coated copper nanoclusters as a demonstration are used to develop a novel detection strategy for hydrogen sulfide based on disulfide exchange reactions.The excellent analytical performance of the established method proves the feasibility and practicability of functional copper nanoclusters with a core-shell structure in long-term sensing and bioimaging applications.(2)Distinctive aggregation-induced emission(AIE)phenomenon of thiolateprotected silver nanoclusters(AgNCs)has been revealed and shown great potential for exploitation and utilization,but their applications in chemosensing and bioimaging areas serving as a bright luminogen are greatly limited by their ultralow brightness in aqueous solution.Herein,we report a facile fabrication of hydrophobicity-guided selfassembled particles of silver nanoclusters with aggregation-induced emission.A hydrophobic ligand,thiosalicylic acid,was adopted to prepare AgNCs in one-step way,and thiosalicylic acid-capped AgNCs show significant AIE behavior.This AIE property of AgNCs enables it to selectively respond to multiple external stimuli such as solvent polarity,pH and environmental temperature.Hydrophobic nature of thiosalicylic acid as the capping ligands of AgNCs drives a self-assembly process of AgNCs in aqueous solution,which results in formation of self-assembled particles of AgNCs with bright luminescence.Sensitive detection of mercuric ion based on highly luminescent AgNC AIE particles was achieved in terms of strong quenching effect of mercuric ion.Cellular cytotoxicity and luminescent imaging performance of AgNC AIE particles on living cells were also evaluated for the first time.This work demonstrates an example of fabricating AIE particles of silver nanoclusters with bright luminescence guided by a hydrophobic capping ligand,and reveals excellent biocompatibility and bioimaging performance of AIE particles in living cells.(3)Gold nanoclusters(GSH-AuNCs)synthesized with glutathione as ligands are not only water-soluble,but also own many advantages of good stability,low toxicity and good biocompatibility,so they can be used as ideal biosensors in biological systems.In this study,we first synthesized and studied the aggregation induced luminescence properties based on glutathione-gold nanoclusters(GSH-AuNCs)in response to multiple stimuli,such as pH and polarity of the solution.Secondly,the factors that affect the luminescence quenching of metal nanoclusters are explored,such as oxygen,temperature and viscosity.Besides,GSH-AuNCs was designed the luminescent probe aimed to response the minor changes of viscosity and temperature in the testing system.In addition,this material also was used for bioimaging in the human A549 cell,due to small changes in cytoplasmic viscosity.Due to the changes of the microenvironment(pH,temperature,and viscosity)in the biological cells are closely related to the normal operation of life activities,it is of great important for real-time detection of the changes microenvironment.In summary,we have prepared and explored three noble metal nanomaterials with aggregation-induced luminescence properties,and successfully made them the ideal probes in analytical detection and biosensing applications.First,we used the copper nanocluster(CuNCs)synthesized by the thiol methoxysilane as a capping ligand to form a silica shell on the surface by hydrolysis polymerization,thereby achieving an improvement in quantum yields and stability of the copper cluster.Secondly,silver nanoclusters(AgNCs)with aggregation-induced emission(AIE)phenomenon were synthesized by one-pot way and self-assembled into AIE particles by hydrophobic induction for detecting mercury ions and cell imaging.At last,GSH-AuNCs with aggregation-induced emission(AIE)properties synthesized using the water-soluble bio-small molecule glutathione(GSH).The change of the phosphorescence signal and a quantitative relationship can be established between luminescence signal and viscosity and temperature,making it it a reality for real time detecting the change of viscosity in cytoplasmic.