Fabrication Of Quantum Dots@ZIF-8 Composites And Their Fluorescence Sensing

Quantum dots(QDs),with their tunable luminous position and fluorescence stability,have become the most interesting fluorescent sensing materials in the new century.In recent years,fluorescent sensors based on quantum dots have become a hot topic for researchers to pursue.In many emerging porous nanomaterials,the regular arrangement of metallic organic frameworks(MOFs)materials with metal ions or metal clusters as the center and connected by organic crosslinking ligands has become the focus of research.MOFs materials are considered as promising carrier materials because of their tunable pore structure,large specific surface area and high porosity.Therefore,combining QDs with metal-organic framework materials(MOFs)by chemical methods to prepare composite materials brings a new idea for expanding the application range of quantum dots and improving the fluorescence detection performance of QDs.This composite material retains the excellent fluorescence properties of QDs,and has good adsorption properties of MOFs,which is easy to be processed and subsequent experiments.Therefore,the application of QDs@MOFs composites as novel fluorescent probes is of great significance.In this paper,a series of QDs@MOFs composites were prepared by simple and rapid synthesis method,and the detection effect of fluorescence properties of these composites on various harmful substances was explored.The specific research work was as follows:(1)We first synthesized Cd:ZnS QDs according to the literature,than Cd:ZnS QDs@ZIF-8 composites were prepared by in-situ growth method for the determination of copper ions in water system.The shell of ZIF-8 enrich copper ions,which enhance the selectivity of fluorescence detection.In this experiment,Cd:ZnS QDs exchange with Cu²⁺,resulting in fluorescence quenching,and this phenomenon can also be observed in the presence of Mn²⁺,Co²⁺and Ni²⁺.In contrast,due to the specific interaction between Cu²⁺and ZIF-8,only Cu²⁺induced fluorescence quenching of Cd:ZnS QDs@ZIF-8.The rapid response time of Cd:ZnS QDs@ZIF-8to Cu²⁺is 1 min,and the detection limit is 16 n M.It can be used for the detection of Cu²⁺in water samples.The spiked-standard recoveries are 90.1?109.8%.These results indicate that the integration of QDs in ZIF-8 is an effective strategy to improve the selectivity of the fluorescent probe to Cu²⁺.(2)We first synthesized CdTe QDs capped with thioglycolic acid,than CdTe QDs were coated into ZIF-8 material by in situ growth method,and used for the detection of tetracycline antibiotics in the environment,and the fluorescent test paper was also made.In this work,a dual wavelength ratio fluorescent probe was constructed by using the sensitization effect of Zn²⁺and the fluorescence internal filtration effect of tetracycline and CdTe QDs.In the following experiment,chlortetracycline(CTC)was used as the representative to study the sensing behavior of tetracycline antibiotics.After the addition of CTC,the red fluorescence quenching of CdTe QDs was attributed to the internal filtration effect,while CTC showed enhanced green fluorescence under the sensitization effect of Zn²⁺.On this basis,CTC can be detected rapidly and sensitively with a response time of 1 min and a detection limit of 37 n M.CdTe QDs@ZIF-8 has been successfully applied to the detection of CTC in fish and milk samples,and further made into fluorescent strip for easy use.(3)Glutathione(GSH)-capped CdTe QDs were prepared by changing the surface ligation system,and then coated with ZIF-8 to form a composite material similar to the previous work.In contrast to previous work,the interaction of glutathione ligands and uric acid molecules on the surface of CdTe QDs constructs a fluorescently quenched fluorescent probe that specifically recognizes uric acid.In other words,the fluorescence intensity of CdTe QDs@ZIF-8 decreased significantly in the presence of low concentration of uric acid in the environment.After the addition of uric acid,the fluorescence quenching of CdTe quantum dots is attributed to the photoinduced electron transfer effect,that is,after the quantum dots are excited,electrons transfer from the surface ligands to uric acid molecules,which reduces the fluorescence intensity.Under this mechanism,uric acid can be quickly and sensitively detected...