Research And Application Of Detection Methods For Organophosphorus Pesticide Residues In Vegetables Based On Aptasensor

Pesticides play a very important role in ensuring crop quality,but also bring potential threats to environmental protection and food safety of agricultural products.Organophosphorus pesticides（OPs）are the most widely used and the most significant amounts of pesticides in China,and the problem of their excessive residues has become a significant potential risk to vegetable safety.At present,the instrumentation methods are often used to detect OPs residues,but these methods need take a long time and cannot meet the needs of rapid detection.Therefore,it is necessary to establish a series of rapid detection methods to detect OPs residues in agricultural products.Electrochemical aptasensor has attracted much attention due to their high sensitivity,low detection limit,fast detection speed,and simple operation.Traditional electrochemical aptasensor uses single-chain aptamer,but single-chain aptamer tends to intertwine on the electrode surface,hindering the combination of the aptamer and the target substance.The DNA strands selected in this study were designed into two three-dimensional nano aptamer structures for the construction of two electrochemical aptasensors to solve the above problems.At the same time,different nanomaterials were used as signal amplification strategies in the construction of the two aptasensors.In addition,the effects of several main components of common vegetables on aptasensor were also studied.The main research contents and results are as follows:（1）Gold nanoparticles（Au NPs）of about 15 nm were prepared and used to modify the aptamer.Au NPs-three-dimensional nano aptamer structure（TDN）was designed and self-assembled by the base complementary pairing principle.Au NPs-TDN was used to construct an electrochemical aptasensor based on the composite materials of graphene oxide（GO）and polyaniline（PANI）to detect profenofos residues rapidly in vegetables.Due to the mechanical rigidity of TDN,the aptamer was kept in a highly ordered upright state,and an independent probe was designed at each vertex of TDN,which could effectively improve the binding efficiency of the aptamer and profenofos.GO@PANI could improve the electrical conductivity of the electrode surface,which could also improve the sensitivity of the aptasensor.The results showed that the detection limit of the aptasensor was 33.30 pg/m L（S/N=3）,the linear range was1.00×10²ï½ž1.00×10⁷ pg/m L,and the recoveries of the profenofos in vegetables was93.52%～103.21%.In addition,it was found in this study that Vitamins in vegetables had more significant interference with the aptasensor.Among the minerals in vegetables,Fe Cl₃ had little influence on the system,while Ca Cl₂ and Na Cl had a great influence on the system.Peroxidase in vegetables interfered greatly with the aptasensor.（2）The above three-dimensional nano aptamer structure was extended to construct an aptasensor for the simultaneous detection of OPs residues in vegetables.Two kinds of probes were prepared using thionin and 6-（Ferrocenyl）hexanethiol,aptamers and Au NPs.Three-dimensional nano DNA structure（TDS）was synthesized with non-specific DNA chains.Based on these,an electrochemical aptasensor was constructed to detect profenofos and diazinon simultaneously.The partial complementary base sequences of profenofos aptamer and diazinon aptamer formed a single-stranded structure on the TDS.This single-stranded structure was called a complementary chain.When there were no target pesticides,the probes bound with the complementary chain.In the presence of the target pesticides,the probes could bind to the target pesticides and were separated from the TDS,which was because the binding force of the probes with the target pesticides was stronger than that of the probes with the complementary chain.Then the concentration of target pesticides was quantitatively analyzed by the change of peak current.In addition,the composite of carboxylated multi-walled carbon nanotubes and ferroferric oxide nanoparticles was used as a signal amplification strategy to improve the sensitivity of the aptasensor.Under optimal conditions,the detection limits of the aptasensor were both 3.33 pg/m L（S/N=3）,and the linear ranges were both 1.00×10¹ï½ž1.00×10⁷ pg/m L.The aptasensor could simultaneously detect the residues of profenofos and diazinon in vegetables.The recoveries were 87.15%～117.34%and 91.20%～114.19%,respectively.The above research provided a variety of detection methods for the rapid detection of OPs,and also studied the influence of vegetable components on aptasensor,which could meet the needs of different people in different scenarios for the rapid detection of OPs residues in vegetables.