A New Method Of Fluorescence Detection Based On Two-dimensional Metal-organic Framework Nanosheets Peroxidase Mimics

Due to the limitations of natural enzymes such as the high cost,low stability,and storage difficulties,the research of artificial enzymes has been concerned.Metal-organic frameworks(MOFs)are porous crystalline materials formed with the coordination bonds between metal/metal clusters and organic ligands.They have large specific surface areas,adjustable pore sizes,modified pore chemical environments,and good thermal stabilities.However,for the application in the aqueous phase,such as enzyme mimics,the water solubility of bulk MOFs is poor,and the catalytic reaction often occurs on the surface of bulk MOFs.Two-dimensional MOFs nanosheets are emerging research frontiers in the MOF field.The ultra-thin two-dimensional structure makes the catalytic sites of MOFs almost completely exposed to the surface.Therefore,we applied two-dimensional MOFs nanosheets as peroxidase mimics.The detailed research contents and the mainly results in this dissertation are as follows:1.Copper-based two-dimensional metal-organic framework nanosheets as horseradish peroxidase mimics for glucose fluorescence sensingUltrathin two-dimensional(2D)metal-organic framework(MOF)nanosheets have attracted numerous attention due to their unparalleled advantages sueh as unique structures,large surface areas,good stability and high catalytic efficiency.In this paper,2D Cu(bpy)2(OTf)2 nanosheets(Cu-MOF,bpy?4,4-bipyridine,OTf=trifluoromethanesulfonate)are first utilized to achieve the fluorescent detection for H2O2 and glucose with their intrinsic peroxidase-like activity.The fluorescent biosensor Cu-MOF nanosheets were achieved by the efficient catalysis of non-fluorescent thiamine(TH)to strong fluorescent thiochrome in the presence of H2O2.With the combination of glucose oxidase,highly selective and sensitive fluorescent detection for glucose could be established with a detection limit of 0.41 jiM and two separate linear ranges of 10-100 ?M and 100-1000 ?M,respectively.Furthermore,the developed method has been applied to hmnan serum for the quantitative determination of glucose as a diagnosis indicator of diabetes mellitus.2.Copper porphyrin anchored two-dimensional zirconium metal-organic framework nanosheets for vitamin B1 detectionIn this study,we modified Zr-based two-dimensional MOFs nanosheets(Zr-BTB)with porphyrin ligands containing different metals(Cu,Mn and Ni).The fluorescence detection of vitamin B1 was carried out by using MOFs nanosheets based on ligand active centers as peroxidase mimics.The three porphyrin-metal MOFs nanosheets demonstrated superior catalytic activities to the metal-free MOFs nanosheets,while the nanosheets containing Cu porphyrin ligands are the best amongst three of them.Under alkaline conditions,Zr-based MOFs nanosheets containing Cu ligands could catalyze the oxidation of vitamin B1 to thiochrome under the presence of H2O2.The optimal pH,reaction temperature and reaction time were pH=10,50? and 3 min,respectively.The kinetic measurements showed that the enzyme mimics followed Michaelis-Menten equation,and the fastest reaction rate Fmax was 5.75 yM.s-1 and Km was 0.09 mM.The enzyme activity Fmax is two orders of magnitude higher than the three-dimensional MOF HKUST-1 and is one order of magnitude higher than the natural horseradish peroxidase(HRP),demonstrating good catalytic activity.Km is lower than HKUST-1 and HRP,demonstrating good substrate binding affinity.Based on these feature,we have developed a highly selective and sensitive fluorescence method with this Cu two-dimensional MOFs nanosheets for the determination of vitamin B1.The standard curve is S-shaped,and the linear range were 5 to 100 ?M,100 to 300 ?M,and 300 to 600 ?M,respectively.The detection limit is 0.85 ?M.The vitamin B1 in the multivitamin tablets was determined.Interference experiments showed that the sensor was only specific to vitamin B1,and other small molecules and salts had little effect on the analytical processes.3.Composites of Au nanoparticles and two-dimensional zirconimn metal-organic framework nanosheets as tandem enzyme mimics for glucose detectionIn this study,we synthesized Au nanoparticles onto Cu porphyrin ligand-modified Zr-based two-dimensional MOFs nanosheets to construct the composites of Au nanoparticles and MOFs nanosheets.The TEM images confirmed Au nanoparticles were successfully attached to the surface of Zr-based two-dimensional MOFs nanosheets with an average particle size of 6.5 nm.This composite could successfully realize glucose fluorescence detection based on tandem enzyme mimics.