Construction Of Ratio Fluorescence Biosensor Based On MnO₂ Nanosheets And Detection Of Chlorpyrifos

Organophosphorus pesticides have been widely used in agriculture because of their high insecticidal efficiency,increased crop yield and easy degradation.In this essay,chlorpyrifos is selected as the model analyte for organophosphorus pesticides.Chlorpyrifos（CPF）is a high-efficiency and broad-spectrum organophosphorus pesticide.However,studies have found that it can inhibit the activity of acetylcholinesterase in organisms.This can lead to adverse reactions such as asthma,teratogenicity,and even death in severe cases.Traditional methods for detecting chlorpyrifos include colorimetry,chromatography,mass spectrometry（MS）,enzyme-linked immunosorbent assay（ELISA）,etc.Although it has the characteristics of high sensitivity and strong reliability,it has some shortcomings.For example,it requires expensive equipment,high testing cost,long time,is not conducive to on-site inspection,and requires professional laboratory personnel.In recent years,the rapid development of bio-enzyme sensors has provided alternative solutions to this problem.Compared with the traditional method,the biological enzyme sensor analysis method has the advantages of short time-consuming,simple operation,low cost,and direct on-site detection.In this paper,inspired by the biological enzyme sensor,based on the inhibitory effect of organophosphorus pesticides on acetylcholinesterase,combined with the unique properties of the two-dimensional nanomaterial manganese dioxide,a biological enzyme sensor for the detection of organophosphorus pesticide chlorpyrifos was designed.The experimental results obtained are as follows:（1）Preparation and characterization of MnO₂ nanosheets and copper-silver nanoclusters（Cu-Ag NCs）.In this paper,the template method was used to successfully prepare MnO₂nanosheets and carry out related structural characterization.It was verified that MnO₂nanosheets have oxidase-like activity and fluorescence quenching ability.MnO₂nanosheets can simultaneously adjust the fluorescence intensity of VB₁ and Cu-Ag NCs.Specifically,MnO₂ nanosheets can enhance the fluorescence of ox-VB₁ at 432 nm,and at the same time quench the fluorescence of Cu-Ag NCs at 568 nm to form a ratio fluorescence signal(F₅₆₈/F₄₃₂).Cu-Ag NCs was successfully synthesized by silver doping,and its structure and properties were characterized.Compared with copper nanoclusters（Cu NCs）,Cu-Ag NCs has higher fluorescence emission intensity.At the same time,the salt tolerance and antioxidant capacity are better,and the storage time can be up to two months.（2）Detection of the organophosphorus pesticide chlorpyrifos.Combine MnO₂nanosheets with acetylcholinesterase to construct a biological enzyme sensing system.Acetylcholinesterase hydrolyzes thioacetylcholine to generate thiocholine,which triggers the decomposition of MnO₂ nanosheets.It loses its ability to oxidize and quench fluorescence.After adding chlorpyrifos,the activity of acetylcholinesterase is inhibited,and the decomposition of MnO₂ nanosheets is blocked,which causes the fluorescence of the sensor system to change.By measuring the changes in the fluorescence intensity of Cu-Ag NCs and ox-VB₁ before and after the addition,the results show that the fluorescence intensity ratio of Cu-Ag NCs and ox-VB₁(F₅₆₈/F₄₃₂)has a linear relationship with the concentration of chlorpyrifos.The linear response range is 0-100 ng/m L,and the detection limit is 29.42 ng/m L.Finally,the anti-interference experiment and the standard addition method detect chlorpyrifos pesticides in river water,tap water and vegetables.The recovery rate of addition was 93%-106.2%,which showed that the established sensor had good anti-interference and accuracy.This provides a new way of thinking for the detection of organophosphorus pesticides.