Analytical Application of Copper Nanoclusters and Their Composites

Author:Hu Xue

Supervisor:huang yu ming


Degree Year:2019





Copper nanoclusters(NCs),composing of few to hundred atoms,display unique fluorescent properties.Cu NCs have advantages of photostability,nontoxicity,water-dispersibility,biocompatibility,and long Stokes shift over other fluorescent materials such as organic dye and quantum dots,which are attractive for fluorescent sensing and bioimaging.However,there are several problems for Cu NCs in synthesis and analytical application.For example,compared with other fluorescent nanomaterials,Cu NCs display relatively low quantum yield;Cu NCs are susceptible to pH and salt-concentation,showing poor stability;it is still difficult to seek a simple and controllable strategy for tuning the emission of Cu NCs;the sensitivity and selectivity of Cu NCs-based analytical methods are not satisfied.To address these issues,the synthesis,fluorescent properties tuning of Cu NCs and their application in fluorescent sensor were investigated.The detailed contents of this paper were listed as follow:Ligand-assisted synthesis of Cu NCs with excellent fluorescent properties for fluorescent sensing1.The Cu NCs were prepared by a simple and green hydrothermal method in the presence of GSH serving both as a reducing and protecting agents,and characterized by UV-vis absorption,HRTEM,FT-IR,and XPS.The GSH-Cu NCs displayed a small size,excellent water-dispersibility,good storage stability,good photostability and were stable in the presence of high concentrations of salt.In addition,the GSH-Cu NCs possessed strong blue fluorescence with a quantum yield of 10.6%and exhibited an excitation-independent fluorescence behavior.The zeta potential,TEM,resonance light scattering and dynamic light scattering measurements demonstrated that the Hg2+-induced aggregation of the Cu NCs contributed to the fluorescence quenching of the dispersed Cu NCs.On these findings,a sensitive and selective fluorescent probe was developed for detecting Hg2+in the linear range from 10 nM to 10μM with a detection limit of 3.3 nM.The proposed method has been successfully applied to determine Hg2+content in water sample and food stuff.The results of the proposed method were in good agreement with those obtained by a hydride generation atomic fluorescence spectrometry.2.One-step approach was developed for the fast synthesis of Cu NCs by using dithiothreitol(DTT)as reducing and protecting agents at room temperature.The synthetic process was fast,simple and easy.The DTT-CuNCs were characterized by UV-vis absorption,FT-IR,TEM,XPS,and so on.The DTT-Cu NCs displayed orange fluorescence with a maximum emission at 590 nm while excitation at 360 nm.The aggregation-induced fluorescence enhancement property of DTT-Cu NCs in presence of Al3+was found.On this basis,we developed a simple,sensitive,selective turn-on fluorescent sensor for the detection of Al3+in food samples.Under the optimized conditions,this fluorescent probe displayed a linear range of 0.01-7μM with a detection limit of 0.01μM.The DTT-Cu NCs-based fluorescent probe has been successfully used to assay the content of aluminum in real food samples such as the fried food and pasta.Tuning the fluorescent properties of Cu NCs and improving sensitivity of sensing by forming composites or metal doping3.To further improve the fluorescent properties of Cu NCs,the CuNCs/ZIF-8nanocomposites were facilely prepared by mixing the PEI protected CuNCs with the precursors of ZIF-8.The CuNCs/ZIF-8 possessed better stability and higher fluorescence intensity due to protective and confinement effects of MOFs,which quantum yield was 15 times that of the PEI-CuNCs.It was found that H2O2 could cause much more quenching of fluorescent CuNCs/ZIF-8 than that of PEI-CuNCs,which might result from enriching H2O2 by ZIF-8.The CuNCs/ZIF-8 could be designed as fluorescence probe to selectively and sensitively detect H2O2 with a linear range from0.01 to 1.5μM and a detection limit of 0.01μM,while those with PEI-CuNCs were0.5-30μM and 0.50μM,respectively.Through formation of CuNCs/ZIF-8 hybrid,the sensitivity for the detection of H2O2 increased by nearly 50-fold.Further,we successfully demonstrated the potential application of the CuNCs/ZIF-8 for screening and evaluating activities of oxidase using glucose oxidase as a model.4.Besides improving the fluorescent properties,the process of encapsulating Cu NCs into metal-organic frameworks was also an effective way to modulate the emission of Cu NCs.Several CuNCs/ZIF-8 core-shell nanocomposites with different fluorescent properties were prepared by introducing precursors of ZIF-8 into penicillamine(DPA)protected Cu NCs.It was worthy noted that with the amounts of 2-MIM increasing in the process of the ZIF-8 forming,the original emission of Cu NCs at 627 nm decreased gradually,and the new emission at 450 nm appeared with quantum yields increasing from 7.77%to 17.07%due to the size-dependent quantum limit effect.Moreover,the aggregated states of Cu NCs turned into dispersive state and the sizes decreased gradually.The changes of emission were attributed to Cu-centered energy state increasing from triplet state to singlet state with the sizes decreasing,which resulted in the blue shift of the emission and fluorescence enhancement of Cu NCs/ZIF-8.In basis of Ag+-induced fluorescence quenching of Cu NCs/ZIF-8,a fluorescent sensor has been fabricated for detecting Ag+,which successfully applied to real samples test.5.Metal doping is also an effective way to improve the fluorescent properties and modulate the emission of Cu NCs.Alloy Cu/Ag NCs were facilely synthesized by introducing Ag+during the aggregating process of Cu NCs.The blue shift of the emission from 625 nm to 560 nm occurred in Cu/Ag NCs due to the formation of new excited states from bimetal center.In addition,Ag doping significantly enhances the quantum yield(about 2-fold enhancement),oxidation resistance to air,storage stability,photostability and salt stability of the resultant Cu/Ag NCs.Impressively,MnO2nanowires quench the fluorescence of Cu/Ag NCs,while they enhance the fluorescence of nonfluorescent VB1 via oxidation reaction between VB1 and dissolved oxygen to produce oxVB1 as a nanozyme catalyst.Upon introduction of GSH as a target,the MnO2 nanowires are reduced to Mn2+and lose their quenching capacity and oxidase-like activity,resulting in fluorescence recovery of Cu/Ag NCs and fluorescence decrease of oxVB1.Hence,a ratiometric luminescence signal is obtained,providing a novel ratiometric fluorescent strategy for sensitively detecting GSH.The sensor exhibited a wide linear concentration range from10 n M to 70μM for GSH with a detection limit of 6.5 nM.The ratiometric sensor was successfully used for GSH detection in biological samples.In summary,several Cu NCs with excellent fluorescent properties were prepared in present of different ligands both as reducing and protecting agents.Encapsulating into MOFs and metal doping as effective strategies were utilized to improve the fluorescent properties of Cu NCs and tune the emission of Cu NCs.In addition,several sensitive and selective fluorescent probes were constructed based on the prepared Cu NCs and their composites for practical tests.Therefore,the main contribution of this work is that provide effective way to tune the fluorescent properties of Cu NCs for constructing sensitive fluorescent sensor.These studies would provide new idea for the synthesis of Cu NCs with high quality and extend the analytical application of Cu NCs.