Construction And Analytical Application Of Aggregation Induced Fluorescence Enhanced Copper Nanoclusters

Copper nanoclusters(CuNCs),typically consisting of a few to several hundreds copper atoms,exhibit ultra-small sizes generating the molecular-like fluorescence(FL)properties and widely used in optical sensing,biological imaging,environmental monitoring,optical catalysis and other fields.Compared with other fluorescent materials(such as organic dyes and quantum dots),CuNCs have the advantages of unique luminescence properties,large Stokes shift,good biocompatibility and simple synthesis methods.Relative to its excellent optical properties,the stability of CuNCs is a shortage that needs to be solved urgently for its susceptiblely oxidized surface.In addition,due to the effective non-radiative relaxation of the surface ligands and the internal relaxation motion of the metal resulting the low fluorescence quantum yield of CuNCs,which seriously affects its application performance.Aggregation induced emission(AIE)is an effective and simple way to improve both the quantum yield and chemical stability of metal nanoclusters by limiting the intramolecular motion as well as promoting the excited state relaxation kinetics.At present,CuNCs with AIE effect are mainly obtained by changing the organic solvent,p H value and thiol ligand.However,most of the CuNCs obtained have disordered and uncontrollable morphology,which is not conducive to regulating its optical performance.Therefore,using AIE strategy to acquired CuNCs with high fluorescence quantum yield,favourable stability and controllable optical properties is of great significance for expanding its applications.In this paper,we take the research subject as"Construction and analytical application of aggregation induced fluorescence enhanced copper nanoclusters",with the main research work of building an AIE analysis sensor platform around red-emitting thiol-modified CuNCs.It aims to solve the problems of low quantum yield,weak FL intensity,poor stability of CuNCs and the selectivity and sensitivity in analytical applications.Based on the unique AIE properties of thiol-modified CuNCs,the AIE system is constructed through ion induction and electrostatic attraction to obtain CuNCs with high luminescence and high stability at the first.Immediately thereafter,combined with the fluorescence characteristics of the newly synthesized CuNCs,a new platform for fluorescence analysis applications was developed and successfully applied to actual sample detection.The specific research contents are as follows:1.Tb³⁺tuning AIE self-assembly of copper nanoclusters for sensitively sensing trace fluoride ionsHerein,we reported that Tb³⁺ions prompt a rapid synthesis of highly emissive CuNCs from weakly luminescent ones driven by AIE mediated self-assembly of CuNCs.The weakly emissive GSH-CuNCs were initially synthesized via a one-step route using glutathione(GSH)as reducing agent and stabilizer.The complexation between Tb³⁺and the carboxyl groups of GSH on the surface of GSH-CuNCs reduced the nonradiative relation of excited state by restricting the intramolecular rotation-vibrational motion,resulting in the formation of the highly red emissive Tb³⁺-CuNCs with over 260-fold emission amplification.Moreover,the Tb³⁺-CuNCs exhibited better storage stability and 14-fold increased in quantum yield relative to the GSH-CuNCs,which played a crucial role in the further application for F^-sensing.The FL of Tb(III)-CuNCs was remarkably quenched upon the addition of F^-due to its strong coordination with Tb³⁺.On this basis,a new assay was constructed for the selective and sensitive detection of F^-.The limit of detection for F^-was 10 nmol/L,which was far below the World Health Organization permissible minimum level of63.16?mol/L in drinking water.The Tb(III)-CuNCs-based FL assay had been successfully used to detect F^-in real samples with satisfactory result.2.Self-assembly of chitosan-mediated copper nanoclusters in hydrogel for ultra-sensitive detection of mercury(II)ions.Herein,we utilized the combination of AIE with self-assembly strategy to quickly synthesize the CuNCs immersed in a hydrogel with highly luminescence.Initially,GSH was used as the reducing agent and stabilizer to synthesis weak emitting GSH-Cu NC.The negatively charged GSH-CuNCs were cross-linked with the introduced cationic polymer chitosan(CS),following impregnated in CS hydrogel to form high luminescence and high stability CS-CuNCs.The intense electrostatic attraction between GSH-Cu NC and CS caused GSH-CuNCs to aggregate in the CS hydrogel,resulting in 18-fold magnification of the fluorescence emission of CS-CuNCs and 9-fold increases to the quantum yield.Moreover,the prominent oxidation resistance,unparalleled salt stability,and fascinating photobleaching properties were the fundamental guarantees of CS-CuNCs in practical applications.Interestingly,the FL of CS-CuNCs will be quenched sharply when Hg²⁺was present.On this basis,the FL probe was constructed for ultra-sensitive detection of Hg²⁺with ultralow detection limit of 0.09 nmol/L,which was well below the drinking water threshold levels(10 nmol/L)and other sensing methods.This proposed method exhibited high selectivity for different metal ions,and had been successfully applied to the detection of Hg²⁺in three different water samples with satisfactory results.