Preparation And Application Of Fluorescent Nano-sensors Based On Metal Organic Framework Packaging Luminescent Materials

Metal organic framework（MOFs）are porous crystal materials consisting of organic ligands and metal ions/metal clusters.MOFs possess both the flexibility of organic materials and the rigidity of inorganic materials.Moreover,MOFs have good biocompatibility,adjustable pore size and pore structure,and large specific surface area,so they are widely used in many fields,such as gas adsorption,heterogeneous catalysis,energy storage,biomedical imaging,drug delivery,etc.In addition,due to the special structure of MOFs,they can adsorb and enrich analytes,encapsulate nanomaterials,and undergo dissociation in specific environments.Currently,MOFs have also attracted extensive attention of researchers in the field of chemical sensing.In this paper,two fluorescent nano-sensors were designed and synthesized based on metal organic framework packaging luminescent materials.And we used them for the detection of molecules and ions.The specific researches are shown as follows:In the first work,a fluorescent sensor CQDs/AuNCs@ZIF-8 with dual-wavelength emission was designed and synthesized for the detection of phosphate.Gold nanoclusters（AuNCs）and carbon quantum dots（CQDs）were encapsulated into zeolitic imidazolate framework-8（ZIF-8）by self-assembly.After encapsulation,the fluorescence signal of AuNCs was enhanced due to the aggregation-induced emission（AIE）properties,while that of CQDs was weakened due to the aggregation-caused quenching（ACQ）characteristics.When phosphate was added,it could decompose ZIF-8,thus leading to the release of AuNCs and CQDs,weakening the fluorescence signal of AuNCs,while restoring that of CQDs.Therefore,with the addition of phosphate,the ratio of fluorescence intensities(F₄₅₈/F₅₈₀)of the two luminescent materials at their respective emission wavelengths changed.The relationship between the ratio and phosphate concentration was calculated to achieve quantitative detection of phosphate.The linear detection range of the fluorescent sensor was 1-120μmol L^-1,and the detection limit was0.27μmol L^-1（the correlation r was 0.998）.The sensor had the advantages of simple preparation,good dispersion,and fast response speed,and had been used for the detection of phosphate in actual water samples.In the second work,a fluorescent sensor AuNCs@ZIF-8 was designed and synthesized for the detection of iron ions.Qwing to the advantages of high adsorption and aggregation capability of MOFs,AuNCs were encapsulated into ZIF-8 to achieve the quantitative detection of the detected substances.After encapsulation,the fluorescence signal and fluorescence lifetime were of AuNCs were significantly enhanced due to its AIE properties.In addition,the fluorescence intensity and fluorescence life of AuNCs@ZIF-8 are significantly enhanced after encapsulation.ZIF-8 is a porous material.After the addition of iron ions,iron ions could enter ZIF-8.There are a large number of amino groups and carboxyl groups on the surface of AuNCs.The nitrogen atoms in the amino group and the oxygen atoms in the carbonyl group can coordinate with iron ions,resulting in the quenching of the fluorescence of AuNCs by iron ions.Therefore,as the addition of iron ions,the fluorescence signal of AuNCs@ZIF-8 gradually decreased.The change value of fluorescence intensity of AuNCs at 583 nm was calculated to achieve quantitative detection of iron ions.The linear detection range of the fluorescent sensor was 1-12μmol L^-1（the correlation r was 0.997）,and the detection limit was 0.61μmol L^-1.The sensor also had the advantages of simple preparation,good dispersion,and fast response speed,and had been used for the detection of Fe³⁺in actual water samples.