An Aptamer-SERS Method For Trace Isocarbophos Based On Iron Metal Organic Framework Loaded Liquid Crystal Nano-catalytic

Organophosphorus pesticides have the advantages of high insecticidal efficiency,low cost and can significantly improve crop yield.They are widely used in modern agricultural production.However,organophosphorus pesticides can cause human poisoning through the digestive tract,skin and respiratory tract,and can remain in the environment for a long time.Based on this,the sensitive determination of organophosphorus pesticides in environment and food is particularly important for food safety and human health.The application of metal organic frameworks（MOFs）as nano enzymes in the field of chemical analysis is a research hotspot in recent years.MOFs not only have the rigidity of inorganic materials and the ductility of organic materials,but also have many functions,such as adjustable porosity,large specific surface area,excellent thermal stability and abundant metal sites.Post modification encapsulation of guest enzymes gives MOFs more extensive application value,which is favored by many researchers.Liquid crystals（LCs）is a special material with both liquid fluidity and crystal anisotropy.It is widely used in the development of optical sensors because of its excellent optical,electrical and thermodynamic properties.However,there are relatively few studies on the application of liquid crystal materials as nano enzymes and the combination of liquid crystal and metal organic framework to form composite nano materials with high catalytic performance.In this paper,iron-based metal organic framework（femof）supported liquid crystal nanocomposites were applied to catalyze the nano silver indicator reaction.The reaction product Ag NPs had significant SERS enhancement effect.Combined with the regulation of aptamer on the catalytic activity of nano enzyme,an analysis platform for the detection of parathion by SERS technology was designed and successfully applied to the analysis of environment and food.The details are as follows:At room temperature,trimesic acid,ferrous sulfate and four liquid crystals（CBT/5CB/MBBA/OCTB）were used as precursors to synthesize iron-based metal organic framework supported liquid crystals materials Fe MOF@LCs（Fe MOF@CBT/Fe MOF@5CB/Fe MOF@MBBA/Fe MOF@OCTB）with high catalytic activity.The loading amount of liquid crystal in Fe MOF was optimized.The addition of liquid crystal improves the structure of Fe MOF,exposes more metal active sites and introduces more electrons.Firstly,transmission electron microscopy（TEM）,energy dispersive spectroscopy（EDS）,X-ray diffraction（XRD）,particle size analysis,potential analysis,BET,molecular spectroscopy（SERS,RRS,Abs,FT-IR）and other techniques were used to characterize Fe MOF@LCs.The results show that Fe MOF crystals with high crystallinity have been synthesized and the liquid crystal has been successfully loaded.After,different alcohols have different degrees of reduction effect on silver nitrate.Eight common alcohols including ethanol/ethylene glycol/glycerin/PEG200/PEG400/PEG600/PEG1000/PVA were screened.The results show that PEG400 is the most sensitive reducing agent.Subsequently,Fe MOF,LCs and Fe MOF@LCs were used to catalyze the REDOX reactions of PEG400 and silver nitrate,respectively.By comparing the slope of the working curve,it was found that Fe MOF@OCTB₄ had the strongest catalytic activity.The yellow silver nanoparticles（Ag NPs）produced by the nanosilver indicator reaction have high surface enhanced Raman scattering（SERS）,resonant Rayleigh scattering（RRS）and surface plasmon absorption（Abs）signals.When Apt _IPS were added to the reaction system,Fe MOF@LCs and Apt IPS are bound by electrostatic adsorption.The catalytic activity of Fe MOF@LCs was significantly inhibited,resulting in a decrease in the output of Ag NPs and a significant weakening of SERS/RRS/Abs signal intensity.When the target molecule IPS was added,aptips preferentially binds to IPS,Fe MOF@LCs were released and the catalytic activity was restored,and the SERS/RRs/Abs signal was enhanced.Based on this,a highly selective and sensitive aptamer-SERS/RRS/Abs three mode analysis platform for the determination of isocarbophos by Fe MOF@LCs nano-catalytic amplification was established.The SERS analysis platform has the highest sensitivity,which can detect IPS in the concentration range of 0.02-1.2n M,and the detection limit is 0.015n M.In addition,the SERS analysis platform with changed aptamers can also be applied to the quantitative detection of glyphosate and malathion.Finally,the selectivity of the analytical platform was investigated with interfering substances,and the analytical platform was applied to the detection of IPS in real samples,which proved the feasibility of the analytical method in practical application,and provided a reference for the detection of trace organophosphorus pesticides in environment and food.