Novel Fluorescent Biosensing Methods Based On Self-Assembled Copper Nanoclusters

Aggregation induced emission materials overcome the quenching effect caused by aggregation of traditional luminescent materials and have a broad application prospect in the fields of biochemical analysis,biosensors and biological imaging.Fluorescent metal nanoclusters not only can effectively overcome the shortcomings of poor stability of organic dye markers and potential toxicity of semiconductor quantum dots,but also have many excellent properties,such as excellent luminescence performance,adjustable emission wavelength,large stokes displacement,good biocompatibility and optical stability.Compared with gold and silver nanoclusters,the raw materials used to synthesize copper nanoclusters are relatively cheap,abundant and easy to obtain.Combination aggregation induced emission excellent luminescent properties,this paper adopts thiophenol compounds as protection of distribution system for the self-assembly fluorescent nanometer copper clusters,using self-assembly fluorescent copper nanoclusters as a fluorescence probe signal,to build a series of high sensitivity,simple,novel method of chemical biology sensing,used for metal ions(such as mercury ions)and biological molecules(such as glutathione,tetracycline)sensitive detection.The main innovations and research contents are as follows:(1)A novel fluorescence strategy and test strips have been demonstrated for the determination of Hg(Ⅱ)ion by using the excellent luminescence properties of the self-assembled fluorescent copper nanoclusters.The self-assembled copper nanoclusters with high stability were synthesized by using 4-chlorophenol as the protective ligand.The fluorescence signal of the copper nanocluster can be quenched by Hg(Ⅱ).Quenching is mainly ascribed to the formation of stable complex formed via Hg-S bonding between the Hg(Ⅱ)ions and the ligand,which destroyed the ordered architectures of self-assembled copper nanoclusters.The assay enables Hg(Ⅱ)to be determined with good sensitivity and a linear response ranging from 1 to 500 nmol/L,and the detection limit of 0.3 nmol/L.In addition,the method was implemented in a test strip((the color of the paper changes from red to blue)that can be used for visual determination of Hg(Ⅱ)in complex environmental water samples.(2)Based on the characteristics of fluorescence enhancement induced by self-assembled fluorescent copper nanoclusters,a novel signal-enhanced fluorescence biosensor was developed for the sensitive detection of intracellular glutathione.The self-assembled copper nanoclusters were synthesized by using 4-methylthiophene as the protective ligand and hydrazine hydrate as the reducing agent.When glutathione was present in the sensing system,the fluorescence signal was significantly enhanced.Due to glutathione regulating the aggregation of self-assembled copper nanoclusters,resulting in aggregation induced emission enhancement.The turn-on fluorescent strategy determined the glutathione concentration in the range from 1 to 100 μmol/L with the limit of detection of 300 nmol/L.In addition,the method can be applied to the determination of intracellular glutathione levels in three parallel measurements with a relative standard deviation of less than 5%.(3)Using the special spatial structure of self-assembled fluorescent copper nanoclusters,a novel non-labeled fluorescent biosensor method was developed for the highly sensitive detection of tetracycline.When self-assembled fluorescent copper nanoclusters were present in the sensing system,the fluorescence signal of tetracycline was significantly enhanced.The fluorescence enhancement phenomenon is mainly attributed to the fact that tetracycline can diffuse into the compatible space of the self-assembled fluorescent copper nanoclusters,the free intramolecular vibration and rotation of tetracycline molecules could be restricted and the non-radiative relaxation decreased,leading to fluorescence emission enhancement of tetracycline.The linear range from 0.2 to 50 μmol/L,and the detection limit is 40 nmol/L.In addition,the method can be applied to the determination of tetracycline antibiotics in urine samples,and the standard recovery rate is 97.4% ～ 105.0%.