Detection Of Organophosphorus Pesticides By Surface-enhanced Raman Spectroscopy Combined With Electrochemistry Based On Nucleic Acid Aptamer Sensor

Deoxyribonucleic acid（DNA）is an organic compound with a complex molecular structure,which is the genetic material of most living organisms.Aptamers are single-stranded DNA or RNA that can specifically bind to a target substance with high affinity.Pesticides have obvious biological effects and do great harm to human body and environment.Surface-enhanced Raman spectroscopy（SERS）has the advantages of simple operation,high sensitivity,fast and non-destructive,which can be used for the rapid detection of pesticide residues.Electrochemical method（EC）is an effective method for pesticide residue detection due to its advantages of low cost,fast response and environmental friendliness.However,a single analysis method has certain limitations and can’t satisfy the research of complex system.In this study,SERS and EC were used to prove the specific recognition of organophosphorus pesticides by aptamers;DNA base insertion and deletion mutations were detected using our improved enhanced substrate.It mainly includes the following three contents:1.Aptamer-based sensor for specific recognition of malathion in fruits and vegetables by Surface-enhanced Raman spectroscopy and electrochemistry combinationSERS and EC were used to prove the specific recognition of malathion by aptamer.The aptamer sensor directly detected the aptamer,malathion,and aptamer-malathion through the SERS method.Differential pulse voltammetry（DPV）and cyclic voltammetry（CV）were used to recognize malathion.Based on the differences in SERS characteristic peaks before and after the combination of malathion and aptamer,a detection method for Malathion specific recognition in complex systems was established.The identification mechanism was discussed.The method was applied for the detection of malathion in spiked apple and bell pepper samples.The results showed that the recoveries were 89.8%～106.5%and the relative standard deviations were 2.5%～6.9%.The method has good reproducibility and the minimum detection limit is 1.6×10^-6mol/L.The method is simple,accurate and reliable,and can be used for the determination of malathion residues in food and environment.2.Detection of chlorpyrifos residue in apple and rice samples based on aptamer sensor:Improving quantitative accuracy with partial least squares modelIn order to improve the accuracy of quantitative analysis,The main goal of this study was to develop an aptamer sensor,SERS and EC methods were used to prove the specific recognition of chlorpyrifos by an aptamer.The partial least squares（PLS）model is introduced in the spectral data analysis to solve the interference problems,so that the developed aptamer can achieve fully selective quantitative analysis.The model is applied to the labeled samples of apple and rice.The results showed that the recoveries were 92.6%～112.5%,the relative standard deviations were 3.2%～9.6%,and the predicted root mean square errors of samples were 5.75 and 5.35,respectively.With the content of real pesticides as reference,t test showed that the method had no significant difference at the level of 1%significance.The developed aptamer sensor can serve as an unlabeled method for detecting pesticides in samples,effectively controlling the quality and safety of food.3.Label-free detection of ss DNA base insertion and deletion mutations by Surface-enhanced Raman spectroscopySERS as a label-free,highly sensitive analytical method,has become an important tool for providing substance fingerprints.In this study,silver nanoparticles containing thiosulfate ions and calcium ions（Ag@SCNPs）have been used as an enhanced substrate to eliminate the interference of impurities on DNA signals.Intrinsic structural information on single-strand DNA（ss DNA）was directly obtained through SERS.The improved enhancement system was used to explore the base-stacking rules of ss DNA in a solution environment.The insertion mutation and deletion mutation of single base and their exact mutation sites were detected.Raman spectra with high stability,repeatability and high signal-to-noise ratio were obtained.The method is fast,accurate and the detection process is nondestructive.It has potential to be applied in the fields of medical diagnosis and genetics research.