Research On A New Sensor Method Based On Porphyrins And Its Array For Pesticides Residues Detection And Its Mechanism

As the most effective, convenient and economical control, pesticides play key rolesin agriculture. However, large-scale use of pesticides seriously threaten ecologicalenvironment, personal health and even social security. Although traditional detectiontechniques show the advantages of high sensitivity and reliability, they requiretime-consuming analysis, expensive instruments and highly trained personnel, which isunsuitable for field analysis. Therefore, rapid and sensitive detection methods ofpesticides become more and more important. In this thesis, the study was not onlyfocused on the selection of porphyrins and the interaction of porphyrins with pesticides,but the preparation and application in the detection of pesticides of nano-porphyrinswere also explored to prepare a novel array sensor based on nano-porphyrins array andrealize the qualitative and quantitative detection of pesticides finally. Researches werecarried out as follows:(1) The responses of porphyrins for five common pesticides were investigated withUV-Vis absorption spectroscopy. As the results showed, ZnTPP was sensitive tolindane, carbendazim, and deltamethrin. CoTPP was sensitive to triadimefon, lindane,carbendazim, and deltamethrin. But there was not any apparent response in theCoTPP-chlopyrifos system. MnTPPCl was sensitive to chlopyrifos, carbendazim, anddeltamethrin. Considering the cross reactivity of sensor array, ZnTPP, CoTPP andMnTPPCl could be used as sensing material for the preparation of visualized sensorarray.(2) According to the optical properties of porphyrins, the colorimetric array sensorwas created. Cross-reactivity of multiple sensing elements can improve the ability todiscriminte several different pesticides. The6×6sensor array was prepared byhandiwork spotting to detect pesticides. Owing to the obvious colour changes of thesensor arrays, the characteristic difference maps of every analyte were gained. RGBdata from the sensor array was analyzed with pattern recognition methods, includingprinciple component, hierarchical cluster and discriminant analysis. As a result, that thedetection of pesticides with the sensor array showed good repeatability, and the fivepesticides can be completely distinguished. Qualitative detection of pesticides could beobtained with this sensor array. (3) To evaluate the detection mechanism with porphyrins, the interaction ofporphyrins with peticides were investigated with molecular docking method andUV-Vis absorption spectroscopy. Computational simulation demonstrated that π-πinteraction, which resulted from the macro-structure as well as the substituted benzenering in the porphyrin systems with the benzene structures of the pesticides, contributed alot to their affinity. In addition, it was found that the strongest binding occurred in thesystems of MnTPPCl-chlopyrifos, MnTPPCl-triadimefon, CoTPP-lindane,ZnTPP-carbendazim, and MnTPPCl-deltamethrin. The binding constant was5.73×108,8.51×107,3.04×108,8.02×107and1.53×108, respectively. These results were consistentwith the detection results.(4) Based on the principle of self-assembly, nano-MnTPPCl and nano-CoTPP weresuccessfully prepared by the mixed-solvent method, and nano-ZnTPP was prepared bysurfactant-assisted self-assembly method using poly (ethylene glycol) as surfactant.Three porphyrin nanomaterials were characterized using FE-SEM. Nano-MnTPPCl wasdisc-shaped nanoparticles, and the average particle size was150nm. Nano-CoTPP wasrod-like nanoparticles, with the average width of100nm and the length of700nm.Nano-ZnTPP was irregular nanoparticles, and the average diameter was300nm.Because of the nanometer effect of nanoparticles, the fluorescence intensity of threenano-porphyrins (MnTPPCl, CoTPP and ZnTPP) was stronger than that of porphyrinmonomer with2.37,2.13and5.22times, respectively.(5) The sensitivity of nano-porphyrins for five common pesticides, were studiedwith UV-Vis absorption and fluorescence spectroscopies. The results indicated thatnano-CoTPP was sensitive to triadimefon and carbendazim. But there were not anyapparent responses in the CoTPP-three other pesticides systems. Nano-MnTPPCl andnano-ZnTPP showed good sensitivity to all the five pesticides. Expect the systems ofnano-MnTPPCl-triadimefon and nano-ZnTPP-deltamethrin, there were good linearrelationship in other nano-porphyrins-pesiticides systems. Therefore, nano-porphyrinswere considered to be sensing material for quantitative detection of pesticides.