Research On Rapid Detection Of Pesticide Residues By Interface Self-assembly Enhanced Raman Spectroscopy

Residual of agrochemicals in agricultural goods,poses a fatal threat to human health and the eccosytem,thereby,reliable and rapid detection techniques are crucially needed.Surface-enhanced Raman scattering（SERS）,which fully combines the technical advantages of Raman spectroscopy and nano-optics,has attracted more and more attention in pesticide residue detection.Substrates with high sensitivity,good reproducibility,and high stability are critical for SERS detection of chemical contaminants in agricultural matrices.Therefore,aiming at the sensitivity,reproducibility and stability of SERS substrates,the bimetallic silver-coated gold nanoparticles（Au@Ag NPs）constructed in this paper were used as the research basis.The liquid-liquid interface co-assembly array behavior of Au NPs and Au@Ag NPs was explored.The detection effect of self-assembled substrates on low adsorption capacity targets was studied by chemical functionalization.The SERS performance of the Au@Ag-4MBA nanoarrays stabilized by the polymer film was investigated.The commonly used pesticides in agricultural production（thiram,thiabendazole and hexachlorocyclohexane）were used as model pesticides to study the response performance of the constructed SERS substrate on pesticide residues in agricultural products.（1）Fabrication and application of liquid-liquid interface co-assembled arrays of Au NPs and Au@Ag NPs.The 30 nm Au NPs were used as the inner core,and a certain thickness of Ag shell was grown on the surface of the Au NPs by the seed growth method to form Au@Ag NPs.COMSOL simulated the relationship between SERS electromagnetic field enhancement and Ag shell thickness.The optimal thickness of the Ag shell（8 nm）was determined using R6G as the signaling molecule.Chloroform as the organic phase and pesticides as the inducer could successfully assemble the Au NPs and Au@Ag NPs in the aqueous phase to form efficient three-dimensional nanoparticle arrays to form metalloid droplets.The gaps between adjacent nanoparticles were tight,which facilitate the feasible formation of numerous SERS"hot spots"between adjacent nanoparticles.The Raman intensity RSD value at 1384 cm^-1of the substrates prepared in different batches was 11.69%,indicating that the liquid sensor has good uniformity and signal reproducibility.The substrate was used for the detection of thiram and thiabendazole in apple puree with detection limits of 0.010 ppm and 0.025 ppm,respectively,with recoveries ranging fromand 97%to 128%.（2）4-Mercaptophenylboronic acid-modified bimetallic liquid sensor for highly reproducible and ultrasensitive detection of hexachlorocyclohexane.4-MPBA modified bimetallic liquid sensor was formed using 4-MPBA modified Au@Ag NPs.Experiments revealed that the 4-MPBA modified substrate was combined withδ-HCH through a cross-coupling reaction,which significantly enhanced the affinity of the substrate for HCH.The 4-MPBA functionalized Au@Ag NPs array exhibited good signal uniformity and repeatability,as demonstrated by 15 randomly collected Raman characteristic spectra with an RSD of 8.29%at the characteristic peak 633cm^-1.The Au@Ag NPs arrays functionalized without 4-MPBA showed a weaker affinity for HCH,while the Au@Ag NPs arrays functionalized with 4-MPBA had a significantly higher affinity for HCH.The detection range of the substrate for HCH was 6.25 to 625 ppb,the linear equation was Y=0.31017x+1.68464,and the R²was0.996.（3）Au@Ag-4MBA nanoarray substrates were constructed based on qPCR membranes and ethylene phthalate（PET）to realize the SERS sensing performance of thiram.The three-dimensional Au@Ag-4MBA nanoarrays in hydrophilic glass bottles were transferred to the qPCR membrane,and a layer of PET film was attached on the substrate surface to form the qPCR/Au@Ag-4MBA/PET substrate.The experimental results showed that the nanoparticle arrangement structure of the obtained qPCR/Au@Ag-4MBA substrate was still dense and uniform,and has excellent SERS sensitivity,uniformity and signal reproducibility.The enhancement factor was 1.16×10⁶,and the RSD value of the SERS characteristic peak intensity at1510 cm^-1between batches was 5.92%.The PET film could protect the inner Au@Ag-4MBA nanoarray from the external environment,effectively improving the storage stability of the qPCR/Au@Ag-4MBA substrate,and the substrate still had more than 90%SERS-enhanced performance after 28 days of storage.The obtained qPCR/Au@Ag-4MBA/PET substrate had good flexibility and could be used for the detection of common chemical contaminants（thiram）.The minimum detectable concentration of this substrate for thiram was 0.0125 ppm,the linear relationship of the linear equation Y=0.48558x+4.12354,and the R²was 0.983.