| Spinach is rich in nutritional profile with significant amounts of vegetable protein,dietary fibre and vitamins,which benefit to health care such as reduction of oxygenfree radical,prevention of cardiovascular diseases and anti-inflammatory.Organophosphorus pesticides are frequently and enormously applied for pest controlling during the cultivation of spinach.The safety and quality of spinach are the most important considerations for manufacturers and consumers.Phorate,profenofos and isocarbophos have been banned in the vegetable production,but their use is still common.Despite their accurate and sensitive performance,traditional techniques also suffer from several limitations,such as complicated sample preparation methods,timeconsuming procedures and interference from organic media.These shortcomings hinder their real-time analysis and quick produce screening.In this study,simple and efficient fluorescence spectroscopy,surface-enhanced Raman spectroscopy(SERS)with unique fingerprint recognition and highly sensitive,magnetic separation technology and aptamer detection system were combined to build highly specific and accurate pesticide molecular recognition detection systems,to realize the rapid qualitative and quantitative detection of pesticide residues.The main research contents and conclusions are as follows:(1)A fluorescence single-channel sensor based on FAM-labeled aptamer system and gold nanoparticles(AuNPs)was used to detect phorate.AuNPs with efficient fluorescence quenching properties were selected as quenchers.Depending on the efficient fluorescence resonance energy transfer between AuNPs and carboxyfluorescein(FAM),the competitive binding of aptamers(OBA)with complementary strand(F-ssDNA)and phorate and steric configuration change of the hairpin aptamer system,the qualitative and quantitative analysis of phorate was carried out by the change of fluorescence signal.The specific interaction between OBA and target phorate induced the change of spatial configuration and fluorescence signal of FssDNA.From 0.02 ?M to 10 ?M,the fluorescence intensity of the system decreased linearly with the increase of phorate concentration,and the limit of detection(LOD)was 15.5 nM.Meanwhile,the sensor has been successfully applied to the determination of phorate in spinach samples,and the recovery was 92.17%-108.87%.The results showed that the fluorescence single-channel sensor has potential application value in the detection of phorate in food.(2)A SERS single-channel sensor based on 4-(methylthio)benzonitrile(MMBN)and aptamer was used to detect profenofos.Using propanophos aptamers(PolyA-Apt)and MMBN modified AuNPs(13 nm)as signal probes and complementary chains(SHcDNA)as substrate,SERS signals were collected on silicon wafers with silver nanoparticles(AgNPs),The qualitative and quantitative analysis of profenofos was carried out by the change of SERS signal.In this chapter,MMBN with strong vibration in the cell silent region(1800-2800 cm-1)was selected as the Raman probe to effectively avoid the interference of other substances in complex biomolecules.Furthermore,it combined with the aptamer systems with strong selectivity and stable structure;The introduction of sequence of PolyA made the assembly of aptamers and metal nanoparticles more efficient and orderly.In the range of 0-50 nM,the SERS signal intensity of the system decreased linearly with the increase of profenofos concentration,and the LOD reached 1.68 nM.Meanwhile,the sensor has been successfully applied to the determination of profenofos in spinach samples,and the recovery was 99.32-102.54%.The results show that the SERS single-channel sensor could resist the interference of complex system,and had a great application prospect in the trace detection of pesticide residues.(3)A SERS-fluorescence double-channel sensor based on magnetic separation technology was used to detect isocarbophos.This chapter effectively combined the research results of the previous two chapters.The core-shell gold bipyramids@Ag nanoparticles(AuBP@Ag NPs)were polymerized with Raman probe MMBN and aptamers of isocarbophos(Apt)to form specific recognition probes.Core-shell Fe3O4@Au magnetic nanoparticles(Fe3O4@Au NPs)and aptamer complementary strands(cDNA)were prepared by thiol self-assembly to form Fe3O4@Au NPs-cDNA capture probes.The characteristic signals were extracted by magnetic separation technology,and the qualitative and quantitative analysis of Isocarbophos was carried out by the changes of fluorescence and SERS signals.The introduction of Fe3O4 could effectively improve the collection and enrichment performance of the system,strengthen the collection of detection signals and simplify the detection process.In the range of 0-60 nM,the Raman intensity of the system decreased linearly with the increase of the concentration of isocarbophos,and the LOD was 0.78 nM.In the range of 0.02-10 ?M,the fluorescence signal of the system decreased with the increase of isocarbophos concentration,and the LOD was 9.84 nM.Meanwhile,the sensor has been successfully applied to the determination of isocarbophos in spinach samples,and the recovery is 98.45-115.42%.Comparing the performance of the SERS-fluorescence double-channel sensor and the fluorescence single-channel sensor,the SERSfluorescence double-channel sensor had lower LOD and suitable detection range,and has broad application prospects.In this paper,based on the aptamer system and specific Raman probe,fluorescence/SERS sensors were constructed to detect phorate,profenofos and isocarbophos in spinach. |
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