Dual-mode Probe Based Enzyme Cascade Reaction For The Detection Of Organophosphorus Pesticide Residues In Brown Rice And Tea

Brown rice and tea are highly susceptible to pesticide pollution during planting and processing,especially organophosphorus pesticides（OPs）pollution.OPs can effectively control pests and weeds and significantly improve crop yield,but OPs can inhibit the activity of acetylcholinesterase（ACh E）and cause abnormal acetylcholine（ATCh）catalysis,which poses a great threat to human health.Therefore,it is imperative to establish efficient,sensitive,fast and reliable analytical methods to detect OPs.Currently reported OPs analysis methods,such as fluorescence,colorimetry,molecular imprinting,etc.,are mostly single detection mode,and the detection performance is easy to be interfered by various environmental factors,while the dual-mode detection method can provide a variety of information,avoid interference from the external environment,and greatly improve the accuracy and reliability of target detection.Based on this,this thesis designed a ratiometric fluorescence and photothermal dual-mode probe based on enzyme cascade reaction for the efficient and rapid detection of OPs.The main contents are as follows:（1）Manganese dioxide nanosheets（Mn O₂ NSs）were prepared by ultrasonic chemical method based on the redox reaction of 4-morpholine ethanesulfonic acid with potassium permanganate.The physical and chemical properties of Mn O₂ NSs were characterized by transmission electron microscope,atomic force microscope,X-ray photoelectron spectrometer,Raman spectrometer and ultraviolet spectrophotometer.The results show that the prepared Mn O₂ NSs has a two-dimensional sheet structure,a large optical absorption range,good water dispersion and photothermal conversion ability.（2）Based on the oxidase-like activity and photothermal effect of Mn O₂ NSs,a ratiometricfluorescence and photothermal dual-mode probe based on enzyme regulation was constructed with thiamine as the fluorescence response signal and tripyridine ruthenium as the reference signal.OPs reduced the production of the reduction product thiocholine by inhibiting the activity of ACh E,thereby regulating the residual amount of Mn O₂ NSs.With the increase of OPs concentration,the color of probe solution gradually transitioned from red to blue,and the temperature gradually increased,so as to realize visual analysis and quantitative detection of OPs residues.（3）The feasibility of the dual-mode probe was qualitatively analyzed by transmission electron microscopy,ultraviolet spectrum and fluorescence spectrum,and the influence of Mn O₂ NSs concentration,thiamine concentration,p H and other conditions on the fluorescence signal of the probe was explored.Using dichlorvos and chlorpyrifos as OPs models,the detection performance of dual-mode probes was evaluated under optimal conditions.The results show that the developed probe exhibits a sensitive response in a wide linear range of 0.1～8000 ng/m L.The detection limits of dichlorvos and chlorpyrifos in fluorescent mode were 1.13×10^-3 ng/m L and 0.86 ng/m L,respectively,and those in photothermal mode were 1.01 ng/m L and 1.02 ng/m L,respectively.The probe showed good anti-interference and reliability in the recovery experiments of OPs residues in brown rice and tea.The recoveries of OPs in brown rice and tea were 95.00～107.25%and96.00～107.50%,respectively,with relative standard deviation less than 3%.The dual-mode probe with self-verification function is expected to provide more accurate and stable detection results than the single-mode probe,and has a broader application prospect.