Rapid Detection Of Organophosphorus And Carbamate Pesticide Residues Based On Microfluidic Paper-based Analytical Devices

Concerns over pesticide residues in food are dramatically increasing with the prevalent usage of pesticides.The detection of these toxic and pollutant organic chemicals commonly relies on chromatographic methods.However,these methods are generally located in central labs,and are difficult to be applied for rapid and highthroughput screening samples in food circulation area.Therefore,it is significant to develop effective rapid detection methods to support on-site pesticide residue analysis for food safety control.Enzyme inhibition assays with fundamentally simplified operation and distinctly reduced cost and time were widely used in the field of rapid detection of organophosphorus and carbamate pesticide residues.The conventional enzyme inhibition assays generally use an aqueous phase solution as the extraction solvent to avoid the influence of the experiment conditions on the performance of the enzyme behavior.It is well known that most organophosphorus and carbamate pesticides show poor water solubility,but are highly soluble in many organic solvents.Therefore,the low extraction efficiency of pesticide residues by aqueous solutions fundamentally restricts the practical performance of enzyme inhibition assays in real world sample analysis.A novel enzyme inhibition assay which was compatible with organic solvents was established to detect organophosphorus and carbamate pesticide residues in food samples.The developed method ultilized the intrinsic large specific surface area of ?PADs to accelerate the spontaneous evaporation of organic solvents which avoided the solvent contaction with AChE.The main contents are lisited as follows.(1)A method which could be compatible with organic solvents and enzyme inhibition assays was established for rapid detection of organophosphorus and carbamate pesticides.The detection conditions of enzyme inhibition assays was firstly optimized.After that,with precise management of reagent introducing procedure,the solvent effect was fundamentally eliminated.By this means,a rapid pesticide detection method which could be compatible with organic solvents and enzyme inhibition assays was established.With the developed method,individual standard solutions of six representative organophosphorus and carbamate pesticides including chlorpyrifos,phoxim,carbaryl,triazophos,carbofuran and methamidophos(all prepared in the organic solvent)were detected respectivey and the corresponding calibration curves were set up.The LODs of the six pesticides in our method were calculated to be 0.77,0.39,0.25,1.29,0.006 and 1.39 mg/L,respectively.These LOD levels were comparable to those from previous reports with aqueous solutions,which demonstrated a completely eliminated influence of solvents on AChE behavior in our method.(2)Organophosphorus and carbamate pesticide residues in typical food samples were successfully detected with the method established.Four pesticides(including phoxim,carbaryl,carbofuran and methamidophos)individually spiked in head lettuce samples were extracted by acetonitrile and measured by the developed method,respectively.The results were compared with the detection results of the conventional enzyme inhibition assays which used aqueous solution as the extraction solvent.The recovery was found to decrease as log P of the pesticide increased when the spiked samples were extracted by water.Significant discrimination effect emerged among the tested pesticides.When acetonitrile was used to extract the spiked samples,the recoveriess of the four pesticides were all in the range of 75.2%~111.7%.And there was no obvious correlation between the recoveries and pesticides' property.The accuracy and reliability of the method were remarkably improved.(3)Rapid screening of liquid samples with pesticide residues far below the LODs of conventional enzyme inhibition assays was realized.By means of pesticide residue extraction with immiscible-water organic solvents,water and apple juice samples spiked with carbaryl concentration of as low as 0.02 mg/L were visually identified.(4)The matrix interference in the analysis of tea samples,as well as its respective solutions,were investigated.The influence of EGCG,caffeine and Vc on the substrate(IPA),product(indophenol)and enzyme(AChE)were assessed,respectively.The results showed that caffeine had no significant interference with IPA and indophenol,while EGCG and Vc could rapidly fade the color of IPA and indophenol.In addition,it was found that Vc had no obviously influence on AChE activity,but even trace amounts of EGCG and caffeine could significantly inhibit AChE activity.Based on these results,tea sample pretreatment conditions were optimized.By comparing the extraction effect of tea matrix coextracted with different extraction solvents,acetonitrile was chosen as the extraction solvent.After investigating the purification efficiency of different adsorbents on tea matrix,200 mg/mL PVPP and 50 mg/mL GO were chosen as the purification materials,which could effectively eliminate matrix effect of tea samples.Combined with the optimized sample pretreatment conditions,qualitative detection of tea samples spiked with 2 mg/kg of carbaryl was primarily achieved by the developed method.