Synthesis And Luminescent Sensing Application Of Gold And Silver Nanoclusters

Noble metal nanoclusters(MNCs)are ultrasmall particles with a core size of?3nm,featuring a core-shell structure composed of noble metal core and organic ligand shell.Owing to the unique molecule-like properties such as precise molecular structure,discrete electron transition,magnetism,molecular chirality,luminescence,etc.,MNCs especially those Au/Ag NCs have become a research hotspot in the field of nanomaterials.Among these molecule-like properties,the luminescence property of Au/Ag NCs is the most attractive,and have been widely used in heavy metal ion/biomolecule sensing,bio-imaging,disease theranostics,catalysis,energy conversion,photoelectric devices,etc.However,there are still some problems in the synthesis and application of MNCs,which greatly limit the further development of this field.For example,in terms of water-soluble MNCs synthesis,the good solubility of both the reducing agent and metal complexes in water makes the controllable reduction kinetics of MNCs impossible,and the complicated ionic environment could affect the stability of MNCs,leading to the formation of poor-quality MNCs.This phenomenon actually hampers the fundamental and applied studies by employing atomically precise MNCs as research models;In addition,the correlation of the size and composition of MNCs to their luminescence is not completely clear,and the luminescence mechanism and size growth control mechanism of MNCs are still undisclosed;Regarding the luminescent MNCs-based sensing,the luminescence of MNCs is still relatively weak,so how to further improve the luminescence intensity of MNCs and improve their sensing performance are challengeable in the field.In view of the above mentioned three issues,the main research content of this thesis is as follows:(1)To solve the issues including uncontrollable synthesis kinetics and the negative impact of complex ionic environment on the MNCs synthesis,a two-phase method is designed to regulate the synthesis kinetics of Au NCs based on the interfacial diffusion of weakly reductive TBAB(methylborane tert-butylamine complex),achieving the high-quality synthesis water-soluble glutathione(SG)-protected Au₁₅(SG)₁₃,Au₂₂(SG)₁₈and Au₂₅(SG)₁₈ NCs with good size monodispersity.This study provides suitable MNCs models for fundamental understanding on the correlation of MNCs'luminescence and size/composition as well as the applied study in the design of MNCs-based luminescent sensors.(2)In order to evaluate the influence of MNCs'size and composition on their luminescence,Au₁₅(SG)₁₃ NCs are used as a seed model,and successfully transformed into(Au Ag)₁₅(SG)₁₃ and(Au Ag)₁₈(SG)₁₄ NCs under Ag⁺induction by heterogeneous metal doping and environmental regulation.Then,(Au Ag)₁₈(SG)₁₄ NCs are successfully converted to Au₂₆Ag(SG)₁₇(Cl^-)₂ under the condition of Au³⁺ion induction.In this process,the regulation mechanism of MNCs'size and composition is revealed.Subsequently,the positions of Ag atoms in(Au Ag)₁₈(SG)₁₄ and Au₂₆Ag(SG)₁₇(Cl^-)₂ NCs and their influence on luminescence are investigated.It is found that the presence of Ag atoms in(Au Ag)₁₈(SG)₁₄ NCs causes ligand-metal-metal charge transfer(LMMCT),thereby promoting their red luminescence;By contrast,the presence of Ag atoms in Au₂₆Ag(SG)₁₇(Cl^-)₂ could bind the electron-rich Cl^-,leading to the enhancement of their red luminescence via the ligand-metal charge transfer(LMCT).(3)With the purpose of improving the sensing performance of MNCs-based sensors caused by their weak luminescence,a novel MNCs-based luminescent sensor featuring luminescence energy resonance transfer,is developed for Cu²⁺detection by crosslinking the red luminescent Au₂₂(SG)₁₈ NCs with the blue luminescent carbon dots(CQDs).Based on the principle of luminescence resonance energy transfer,the blue luminescence of CQDs can effectively enhance the red luminescence of Au₂₂,and then the specific interaction between Cu²⁺and Au₂₂ causes the luminescence quenching of the probe,resulting in the detection of Cu²⁺with a low detection limit of 4.5?M.