Study And Application Of Two Types Of Surface Enhanced Raman Spectroscopic Composite Substrates

With the continuous development of modern science and technology,the use of pesticides in agricultural production has become increasingly widespread,leading to the possibility of pesticide residue in agricultural products,which can be harmful to human health.Therefore,pesticide residue detection is crucial for people’s livelihoods.Traditional pesticide detection methods,such as HPLC-UV（high-performance liquid chromatography-UV detection）method,CL-ELISA（chemiluminescence enzyme-linked immunosorbent assay）and capillary electrophoresis,require complex sample pretreatment and are time-consuming.Surface-enhanced Raman spectroscopy（SERS）technology can perform non-destructive detection of substances without sample processing,and has the advantages of high detection sensitivity and fast speed.Currently,this method is widely used in pollution detection,water quality detection,medical drug detection,and biological analysis.In recent years,most research on improving the detection accuracy of SERS has focused on preparing different structured substrates.However,traditional SERS substrates have short preservation time,poor reproducibility,and low selectivity.To address these issues,this study innovatively proposes the combination of the advantages of carbon nanotubes,gold,and silver to prepare two types of novel SERS composite substrates.This paper investigates their enhancement mechanism and their applications in pesticide residue detection.The main research contents are as follows:Using hydrothermal method,uniform silver nanoparticles（AgNPs）were prepared on the surface of multi-walled carbon nanotubes（CNTs）to form a CNTs/Ag composite structure.Elongated silver nanowires（AgNWs）were also prepared using hydrothermal method.The CNTs/Ag and AgNWs were mixed and the resulting mixture was dropped onto SiO₂ surface and allowed to dry to form a CNTs/Ag/AgNWs/SiO₂ composite substrate with high sensitivity and good uniformity.R6G was used as a probe molecule to evaluate the performance of CNTs/Ag/AgNWs/SiO₂,and the detection limit for R6G was 10^-12mol/L with an enhancement factor of 8.947×10⁸.The substrate showed good uniformity and stability.The enhancement mechanism was investigated using experimental and FDTD methods.A seed-growth method was used to generate a gold shell on the surface of both AgNPs and AgNWs to form a core-shell structure.The resulting SiO₂ was then combined to form CNTs/Ag@Au/SiO₂ and CNTs/AgNWs@Au/SiO₂ composite substrates with high sensitivity and good stability.R6G was used as a probe molecule to evaluate the performance of CNTs/Ag@Au/SiO₂ and CNTs/AgNWs@Au/SiO₂,and both substrates showed a detection limit for R6G of 10^-11mol/L with enhancement factors of 2.63×10⁶and 4.726×10⁷,respectively.Both substrates showed good uniformity and high stability.The enhancement mechanism was investigated using FDTD methods.The performance of the two types of SERS substrates were compared:the stability of the CNTs/Ag/AgNWs/SiO₂ composite substrate was relatively poor compared to the core-shell structure substrate.However,considering the lower detection limit and higher enhancement factor for R6G,the CNTs/Ag/AgNWs/SiO₂ composite substrate was chosen to detect two pesticides,Furadan and Diquat,and the relationship between the concentration of the two pesticides and the Raman signal was investigated.In order to achieve quantitative detection of Furadan and Diquat pesticides,a model for quantitative analysis of the concentration of the two pesticides was established,and a genetic algorithm was used to optimize the BP neural network,enabling the network to adaptively calculate the learning rate and the number of hidden layer nodes.The results showed that the prediction accuracy of the model for the quantitative detection of Furadan was 92.5%,and for Diquat was 92%.This method has superior performance and great potential in the detection of toxic chemicals,environmental pollutants,food additives,and other applications.