Detection Of Hazards In Grain By Electrochemical Sensor Based On Curcumin Nanocomposites

Grain is a major food crop in China,but it is contaminated during production,processing,transport and storage,and it is important to establish rapid and sensitive methods for the detection of hazards in grain.Electrochemical methods are commonly used for the detection of hazards in grain and have the advantages of fast response time,ease of operation and high sensitivity,enabling effective detection of hazards in grain.The detection of hazardous substances in grain has the problems of low target concentration and strong matrix interference.It is particularly important to find stable signal markers to make the detection results stable and signal amplification,and improve the sensitivity of detection.Curcumin（CCM）is a natural pigment with good electrochemical activity and chemical stability,which can be combined with nanomaterials to improve the sensitivity of electrochemical detection.In this thesis,electrochemical sensors for the detection of the heavy metal cadmium ion(Cd²⁺)and lead ion(Pb²⁺),methyl parathion（MP）and aflatoxin B₁（AFB₁）were constructed by modifying electrodes with curcumin nanocomposites.The details of the study and the results are as follows:1.A ratiometric electrochemical sensor based on curcumin for the detection of cadmium and lead in grainElectrochemical polymerization of CCM on the surface of glassy carbon electrodes modified with multi-walled carbon nanotubes（MWCNTs）/layered hydrotalcites（LDHs）to construct a ratiometric electrochemical sensor for the detection of Cd²⁺and Pb²⁺in grain.LDHs are rich in hydroxyl groups and various interlayer anions,which can enrich heavy metal ions.MWCNTs have a large specific surface area and good electrical conductivity,and the synergistic effect between MWCNTs and LDHs can provide more binding sites for heavy metal adsorption on the electrode surface,thus improving the sensitivity of detection.The introduction of CCM as an electrochemical built-in reference probe reduces matrix interference and impurity interference,resulting in improved electrochemical sensor stability,accuracy,and interference resistance.Based on this,a ratiometric electrochemical sensor was constructed for the detection of Cd²⁺and Pb²⁺based on the ratio of I_Cd²⁺/I_CCM to I_pb²⁺/I_CCM.Under optimal conditions,the limit of detection（LOD）of Cd²⁺and Pb²⁺were 0.61μg/m L and 0.74μg/m L,respectively.We further applied the method to the determination of Cd²⁺and Pb²⁺in rice flour and flour samples and obtained satisfactory recoveries.2.Curcumin-MOF-based electrochemical sensor for the detection of methyl parathion in grainHydrothermal synthesis of metal-organic framework Ui O-66 and preparation of CCM/Ui O-66 nanocomposites by the adsorption of Ui O-66 on CCM.Based on the adsorption and enrichment of MP by Ui O-66 and theπ-πinteraction between CCM and MP,the CCM/Ui O-66 nanocomposite can significantly enhance the sensitivity of electrochemical detection.Based on this,a non-enzymatic electrochemical sensor for the rapid and sensitive detection of MP was constructed.Under optimal conditions,the method was able to detect MP in the range of 20 ng/m L to 20000 ng/m L with a LOD of 0.98 ng/m L.The electrochemical sensor had excellent specificity,stability,reproducibility,and repeatability with recoveries of 97.00%to 110.73%and 97.70%to 114.30%in rice flour and flour spiking experiments,respectively.3.Electrochemical sensor based on curcumin encapsulated with zeolitic imidazolate framework-8 for sensitive determination of aflatoxin B₁in grainThe CCM@ZIF-8/PDA was prepared by embedding CCM in a zeolitic imidazolate framework-8（ZIF-8）structural material using a biomimetic mineralization method and modifying a polydopamine（PDA）layer on its surface.The CCM@ZIF-8/PDA was coupled with Immunoglobulin G（Ig G）to synthesize CCM@ZIF-8/PDA/Ig G.The electrochemical detection of AFB₁was performed by an indirect competitive immunoassay using the signal amplification of the material and the immune recognition of Ig G.Under optimum conditions,with an increase in AFB₁concentration,the electrochemical response values decreased linearly from0.0005 ng/m L to 10 ng/m L,and the LOD was 0.11 pg/m L.Meanwhile,the specificity,stability,repeatability and reproducibility of this electrochemical immunosensor reached an acceptable level,and the spiked recoveries of AFB₁ in rice flour and flour were 86.65%-105.20%and 92.60%-104.60%,respectively.The results of high-performance liquid chromatography（HPLC）were compared with those of the proposed method.The results were consistent with those of the proposed method,which proved the accuracy and practicability of the proposed electrochemical method.