New Methods For Detection Of Organophosphorus Pesticides Based On Ratiometric Fluorescence Sensor

China is a large agricultural country.In agricultural production,pesticides play a huge role in increasing crop output.Pesticide application is one of the important means of protecting crops.Food safety issues are closely related to our health.Because pesticides are toxic,improper use will bring pollution to the environment and affect human health.Acetylcholinesterase（ACh E）is a hydrolase,which mainly exists in the human central nervous system.It can catalyze the hydrolysis of the neurotransmitter acetylcholine and can also undergo a phosphorylation reaction with organophosphorus pesticides.Thus,organophosphorus pesticides can inhibit ACh E activity,which causes disordered production of neurotransmitter acetylcholine and affects human cognitive processes.As a result,human health and life will be harmed seriously.Therefore,the development of simple and rapid methods for detection of organic phosphorus pesticides is essential for preventing and solving food safety problems.The ratiometric fluorescence method can improve the accuracy of target detection by avoiding the interference of the external environment.In view of this,we designed a ratiometric fluorescence sensor for highly sensitive detection of acetylcholinesterase and organophosphorus pesticides.The main contents are as follows:Based on the peroxidase-like activity and redox capacity of manganese dioxide（MnO₂）nanosheets,we constructed a novel ratiometric biosensor for the determination of acetylcholinesterase and its inhibitor organophosphorus pesticides.MnO₂ nanosheets possess the peroxidase-like catalytic activity.Scopoletin（SC）is a fluorescent peroxidase-like substrate,while Amplex Red（AR）is a non-fluorescent peroxidase-like substrate.They are used as probe pairs with opposite responses to the manganese dioxide nanosheets,which can quench the fluorescence of SC and enhance the fluorescence of AR through oxidation.In the absence of organophosphorus pesticides,ACh E hydrolyzes the substrate acetylcholine chloride（ATCh）to produce choline（TCh）and acetic acid.Choline is reductive,leading to the decomposition of manganese dioxide nanosheets,then producing manganese ions(Mn²⁺).SC has a strong fluorescence signal at 465 nm,while AR has a weak fluorescence at 585 nm.In the presence of organophosphorus pesticides,the activity of ACh E is inhibited and the decomposition of manganese dioxide nanosheets is hindered.Therefore,the fluorescence intensity of SC decreases at 465 nm and the fluorescence intensity of AR increases at585 nm.Under the optimal experimental conditions,with the increase of the organophosphorus pesticides concentration,the fluorescent intensity of SC gradually decreases and the fluorescent intensity of AR gradually increases.Moreover,under the irradiation of ultraviolet light,the color of its corresponding solutions changes from blue to red gradually.So,the organophosphorus pesticides can be quantified visually according to the color change of the solutions.Quantitative analysis of organophosphorus pesticides is realized by calculating the ratio of AR and SC fluorescence intensity.This method has a wide linear range from 5.0 pg/m L to 500 ng/m L with a detection limit down to1.6pg/m L,which is superior to the previously reported methods.In addition,this method is more sensitive and rapid,showing a good selectivity for organophosphorus pesticides.It has been also successfully applied to the detection of environmental actual samples,obtaining satisfactory results.The above results indicate that the dual-signal ratiometric fluorescence strategy can improve the accuracy of organophosphorus pesticides analysis,greatly reduce the interference of the external environment,and provide new insight for constructing ratiometric fluorescence biosensors.