| Copper nanoclusters(CuNCs),consisting of a few to tens of copper atoms,have gained great attention in recent years because of its inherent merits including excellent luminescence,straightforward synthetic accessibility and significantly low cost in comparison to silver and gold nanoclusters.A variety of biomacromolecules as the stabilizing ligands,such as DNA oligonucleotides,proteins and peptides,have been used to prepare CuNCs for monitoring biomolecules of interest.Several polymers were also utilized to synthesize colorful CuNCs with the assistance of some specific reductants for sensing metal ions.However,these CuNCs capped with macromolecules or polymers generally possess low emission efficiency,and are not readily accessible to external stimuli like pH and heat.Recent advances on thiol-containing small molecules stabilized CuNCs demonstrated that these CuNCs can be synthesized in a straightforward and facile fashion,and possess unique aggregation-induced emission(AIE)property and specific response to environmental changes.However,the synthesis of CuNCs are still at an early stage in the application and analysis.In this paper,we try to prepare copper nanoclusters with aggregation-induced emission properties by using different thiolcontaining small molecules compounds as ligands.Through the selection of ligands and optimization of synthesis conditions,the synthesized CuNCs for the biological enzyme sensing and detection of trace water in organic solvents.Through a serie of ligand screening,it is known that penicillamine,4-methylthiophenol and 3-mercaptoethyltrimethoxysilane as ligand can be used to prepared CuNCs with aggregation-induced emission property.CuNCs with aggregation-induced emission property is used as a luminescence sensing platform,to detect ultra-low water content in organic solvents,and monitor the activities of acid phosphatase and β-galactosidase in real time.The main contents are as follows:(1)D-Penicillamine was adopted to synthesize CuNCs as both the reductant and capping ligand,and as-prepared CuCNs possess unique aggregation-induced emission(AIE)property.The luminescence of CuNCs is responsive to the change in pH or external temperature.Brightly luminescent CuNC aggregates at low pHs sensitively respond to the presence of oxidative stimuli including high oxidizing potentials and commonly used oxidants such as Fe3+,Ag+ and H2O2.In terms of this specific redox-responsive nature of CuNC aggregates,a novel redox-mediated ACP assay was established.The complex Fe(PPi)2-formed from Fe(Ⅲ)and pyrophosphate ions,which exerts no impact on the luminescence of CuNC aggregates due to its low oxidizing potential,was used as the substrate of acid phosphatase.The presence of acid phosphatase enables pyrophosphate ions in Fe(PPi)2-to rapidly hydrolyze into phosphate and free ferric ions,and the accumulation of free ferric ions prompts the oxidization of copper atoms in CuNC aggregates by ferric ions,where an electron transfer from CuNC aggregates to Fe(Ⅲ)takes place as a redox reaction.The following luminescence quenching occurs because parts of copper atoms in the aggregate are oxidized to Cu(Ⅱ)with higher valence.The ACP level is indirectly correlated to the luminescence quenching efficiency of CuNC aggregates,which is used to establish a quantitative detection assay for ACP activity.(2)a facile synthesis of 4-methylthiophenol protected copper nanoclusters with aggregation-induced emission enhancement characteristic was achieved,and stable and bright luminescent particles were prepared by hydrophobicity-controlled assembly of copper nanoclusters.To overcome the drawbacks of preceding CuNCs capped with hydrophilic ligands that the luminescence can not be retained in neutral and alkaline solutions,we adopted a hydrophobic ligand,4-methylthiophenol,to synthesize hydrophobic copper nanoclusters with the assistance of a reducing agent NH2NH2.Hydrophobicity of the protecting ligand of CuNCs makes it possible to self-assemble into brightly luminescent AIE particles.Weakly emissive CuNCs were first assembled into bright luminescent CuNC particles via hydrophobic interaction.4-Nitrophenyl-β-D-galactopyranoside(NPGal)was selected as the substrate of β-galactosidase.The presence of P-galactosidase triggers the rapid hydrolysis of the substrate into galactose and 4-nitrophenol which could adsorb on CuNC particles and efficiently quench its luminescence.The evaluation of P-galactosidase level can be conducted in this continuous and real-time way.(3)We achieved the ultralow-level water detection in organic solutions through bonding-induced emission(BIE)characteristic of silyl-protected CuNCs in the desirable signal turn-on mode using simple and commercially available reagents.It is interesting found that simply mixing of simply mixing of(3-mercaptopropyl)trimethoxysilane and copper nitrate at room temperature can produce silyl-protected CuNCs where(3-mercaptopropyl)trimethoxysilane serves as the reductant,capping ligand and functional group.This silyl-capped CuNCs show significant aggregation-induced emission(AIE)property,but it is more important to discover its bonding-induced emission behavior(BIE).The luminescence enhancement caused by bonding is more efficient than that induced by physical aggregation.Ultrasensitive detection of water in five organic solvents were achieved combining the hydrolysis reaction of silyl-CuNCs by water and bonding-induced luminescence caused by the following polymerization of generated silicic acid on the surface of CuNCs.In conclusion,we have successfully realized the detection of acid phosphatase by using CuNCs oxidation property.Then,based on CuNCs,a novel method for monitoring β-galactosidase activity under the control of p-nitrophenol was developed by using hydrophobic interaction.Finally,according to the fact that bonding-induced emission is better than the physically aggregation-induced emission,the silyl-capped CuNCs are prepared,the detection of water is based on water-triggered hydrolysis and polymerization of silyl groups of CuNCs and the following bonding-induced emission,so that the luminous intensity is obviously enhanced,and finally the detection of trace water in an organic solvent is realized.This study not only established a detection strategy based on aggregation-induced emission mechanism,but also broadened the application of copper nanoclusters in biological analysis,and provided a reliable and sensitive method to detect hydrolase and trace water. |
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