Application Of Copper And Manganese Metal-organic Gel Derivatives In Alkaline Phosphatase Colorimetric Analysis

Metal-organic gel（MOG）is a new kind of smart soft material,which has attracted more and more researchers’attention.MOG is widely used in many fields because of its high porosity,high specific surface area,low molecular weight and excellent thermal stability.In addition,MOG-derived materials can be obtained by simple physical and chemical treatment of MOG precursors,and MOG-derived materials exhibit excellent physical and chemical properties.For example,MOG-derived materials have rich specific surface area,porous structure,excellent conductivity,highly dispersed active center and other characteristics,which make them have potential application prospect in chemical sensing,adsorption,drug loading,catalysis and biomedicine.Hence,it is a new trend to develop MOG derivatives.At present,the oxides or carbon derived from MOG materials are in the initial stage of development,and the types and characteristics of the derivatives are relatively simple.As a new type of functional nanomaterials,nanozymes are widely used in analytical sensing field.However,complex preparation process and low activity of conventional metal oxide nanozymes and carbon-based nanozymes limited their applications in practical fields.The construction of defect engineering can effectively regulate the catalytic activity of these nanozymes.Therefore,MOG materials are used as precursors to prepare transition metal oxides and carbon-based materials,and defects are introduced during the preparation process,different kinds of enzyme-like materials with different catalytic properties can be obtained.Based on this,the defects-rich metal oxides and metal-doped carbon materials were obtained by pyrolyzing the precursors of Mn-MOG and Cu-MOG.We then explored their catalytic mechanism.As a marker of many diseases,there are many methods to detect the activity of alkaline phosphatase（ALP）,such as electrochemical detection,photoelectrochemical sensing,surface-enhanced raman scattering（SERS）,fluorescence immunoassay.The complexity and high cost of these methods limit their further application,the colorimetric sensor based on nanozymes have attracted much attention owing to their low cost,simple operation and visualization.We have successfully applied MOG-derived materials to the colorimetric analysis of ALP.The detailed research content are as follows:1.Application of oxygen-rich vacancy manganese oxide derived from manganese-based metal-organic gel in ALP colorimetric analysis.The organic ligand was pyromellitic acid（H₃BTC）,and the metal node was manganese ion（Ⅱ）.A white Mn-MOG was obtained by simple mixing of Mn²⁺solution with H₃BTC solution at room temperature.Xerogel（Mn-MOX）was further obtained after removing the aqueous solvent of Mn-MOG with freeze-drying treatment.A series of oxygen-rich vacancy manganese sesquioxide（OVs-Mn₂O₃-X）were obtained by pyrolysis of Mn-MOX as precursor at different temperatures.The results showed that the manganese sesquioxide obtained by calcination at 400℃（OVs-Mn₂O₃-400）had strongest oxidase-like activity.Both the steady-state kinetic constant（K_m）and the catalytic kinetic constant（E_a）of the OVs-Mn₂O₃-400 suggested very strong affinity towards the substrate 3,3’,5,5’-tetramethylbenzidine（TMB）and excellent catalytic activity.The participation of superoxide radicals in the catalytic oxidation of TMB was verified by the free radical inhibition experiment and ESR experiment.In addition,we traced the source of superoxide radicals through hydrogen peroxide probe experiments and Raman spectroscopy,which showed that the superoxide radicals are derived from the decomposition of hydrogen peroxide in the metal active center and the formation of oxygen vacancy triggered by Mn-O bond breaking.Based on the fact that ALP can hydrolyze the substrate ascorbic acid phosphate（AAP）to produce ascorbic acid（AA）,and AA can react with manganese sesquioxide.In addition,AA has the ability to scavenge free radicals,and the oxidase-like activity of OVs-Mn₂O₃-400 is inhibited.A sensitive,selective and visual colorimetric sensor has been successfully applied to the detection of ALP in serum with a linear range of 0.1-12 U/L and a detection limit as low as 0.054 U/L.2.Application of copper-based metal-organic gel/melamine-derived highly active carbon nanozymes in ALP colorimetric sensing.Cu-MOG was synthesized in one step mixing at room temperature by using H₃BTB as ligand and copper ion as metal active center.With melamine as template,Cu-MOX and melamine were mixed,ground and calcined to produce copper-doped carbon materials（Cu-C₃N₄-550）with excellent peroxidase-like activity.On the one hand,the defects of carbon materials are effectively regulated by element doping.On the other hand,the good conductivity of copper is more conducive to electron transfer,and the addition of copper increases the specific surface area of the original C₃N₄ by three times.Hence,the peroxidase-like activity of Cu-C₃N₄-550 increased by 32-fold and 3-fold compared with C₃N₄ and CuO respectively.Based on the principle that ALP hydrolyzed AAP to produce AA,and AA can inhibit the oxidation of TMB.Cu-C₃N₄-550 was successfully applied to the colorimetric analysis of ALP in serum.The linear range was 0.4-20 U/L and the detection limit was 0.32 U/L.This thesis takes MOG as the research point,metal oxides and metal-doped carbon materials with excellent enzyme-like activity were obtained by calcining MOG precursors directly.The enzyme-like activity and catalytic mechanism of MOG-derived materials were discussed in detail,it was found that oxygen vacancy and metal element doping could regulate the catalytic activity of MOG derivative materials.Finally,it was applied to the colorimetric analysis of ALP.These experimental studies not only show that MOG-derived materials have excellent enzyme-like activity,but also provide a new idea for designing activity-enhanced nanozymes.