Colorimetric And Electrochemical Sensing For Glyphosate Based On Copper Porphyrin Metal Organic Frameworks

Glyphosate is a non-selective broad-spectrum herbicide and widely used in the world.In agriculture,glyphosate is often used in combination with genetically modified crops to suppress the growth of competitive weeds,achieving high yields and efficiency at low cost.Overuse of glyphosate poses threat to ecosystems and human health.Therefore,it is of great significance to develop a sensitive and simple method for the determination of glyphosate.Metal organic frameworks（MOFs）,as a kind of new porous crystalline materials formed by metal nodes and organic ligands,has attracted people’s interest.It has adjustable unique structure and function,rich active sites,ultra-high porosity,which has a good application prospect in catalysis,electrochemical sensing.In this paper,a colormetic sensing method for glyphosate in food was established by combining copper porphyrin metal organic frameworks Cu-TCPP with silver nanoparticles（Ag NPs）.In order to improve the sensitivity of the method,Cu-TCPP was modified on carbon paper（CP）electrode and a three-electrode system was used to determine glyphosate,and a fast and sensitive electrochemical sensing method was established.The main content and results are as follows:Firstly,silver nanoparticles modified copper porphyrin metal organic framework nano-enzyme（Ag NPs/Cu-TCPP）was synthesized by solvothermal method and in-situ reduction method,thus a colorimetric sensing method for glyphosate was constructed.The morphology,functional groups,crystal form and elements of Ag NPs/Cu-TCPP were characterized by scanning electron microscopy,transmission electron microscopy,fourier transform infrared spectroscopy,X-ray diffraction and X-ray photoelectron spectroscopy.The excellent peroxidase activity of Ag NPs/Cu-TCPP was investigated by UV-vis spectrophotometer.In the presence of H₂O₂,it would catalyze the oxidation of 3,3’,5,5’-tetramethylbenzidine and the solution turned blue The addition of glyphosate inhibited the nano-enzyme activity and turned the solution from blue to colorless.The catalytic mechanism of Ag NPs/Cu-TCPP was investigated by kinetic experiments.The typical Michaelis-Menten curve of Ag NPs/Cu-TCPP nano-enzyme can be obtained,which is consistent with enzyme kinetics.Under the opitimized conditions,the linear range of glyphosate concentration was from 2 to 400μmol·L^-1,and the detection limit was 0.67μmol·L^-1（S/N=3）.The constructed method has good selectivity and reproducibility.It was successfully applied to the detection of drinking water and cucumber and the recoveries were98.3%～103.5%.Secondly,an electrochemical sensing method for glyphosate based on Cu-TCPP modified CP was constructed.Cu-TCPP has large specific surface areas and excellent catalytic activity,which increases the reaction sites of copper combined with glyphosate for selective determination.The conductivity and active area of different modified CP electrodes were characterized by cyclic voltammetry,electrochemical impedance spectroscopy and differential pulse voltammetry.What’s more,the electrochemical behavior of glyphosate on Cu-TCPP/Au NPs/CP was investigated.p H,Cu-TCPP concentration,enrichment voltage and enrichment time were optimized.Under the optimized conditions,glyphosate was detected by differential pulse voltammetry for 2 min.The detection limit of the sensor is 0.03μmol·L^-1（S/N=3）,and the recoveries of the real samples were 97.5%～110.7%.After two weeks of storage at 4^oC,the peak current of the sensor remained 86.6%of its original value,successfully applied to soybean,wheat,carrot and drinking water.