SERS Substrate Construction Of Silver Nanoparticles And Its Detection Of Bipyridine Herbicides

In 1974,Fleischmann et al.excavated that the surface-enhanced Raman scattering（SERS）spectrum of pyridine molecules attached on the surface of coarse silver electrode.Surface enhanced Raman technology has been extensively applied for the detection of agricultural and food products,biochemical analysis and other fields because of its high accuracy,low detection limit,high detection efficiency and loss free quantitative analysis.In this paper,bipyridine herbicides were selected as representative substances to establish relevant SERS analysis and detection methods.Firstly,this thesis primarily presents the mechanism,preparation,and the utilization of SERS effect and the performance of bipyridine herbicides.Secondly,based on density functional theory（DFT）and Gaussian 09 software,the molecular structures of paraquat and diquat were optimized by B3LYP method,and their Raman spectra were calculated.And then,the theoretical arithmetic Raman signal is consistent with the standard Raman and SERS signal,and their Raman diagnostic peaks came under the jurisdiction of the vibration modes.The change of electric field distribution in metallic nanoparticles was simulated by finite difference time domain（FDTD）algorithm.The data display the electric field intensity in the local surface plasmon resonance region of ellipsoidal silver nanoparticles increases not only with the decrease of particle gap,but also with the increase of the amount of clustered particles.Thirdly,SiO₂@Ag nanoparticles were prepared by reducing agent polyvinylpyrrolidone through electrostatic attraction between silanol groups and silver ammonia ions on the surface of silica microspheres.The particle size and coverage of silver nanoparticles on silica microspheres were adjusted by changing the concentration of precursor[Ag（NH₃）₂]⁺ions.The morphology,size and UV absorption spectrum of SiO₂@Ag SERS substrate were characterized by SEM,UV-vis and XRD.SiO₂@Ag nanoparticles can degrade the target analyte by using the inherent photocatalytic activity of Ag on the surface of SiO₂.The prepared SiO₂@Ag nanoparticles were used as Raman active substrate for the detection limit of the target analyte as low as 10^-9mol/L.Under simulated natural light conditions,paraquat concentration decreased to7.7%of the initial concentration,the concentrations of paraquat free radical,diquat and diquat free radical decreased to 32.7%,36.4%and 17.9%,respectively.Then,the titanium alkanol group（Ti-OH）on the surface molecular chain of TiO₂was opened by chemical reaction,and then the silver ammonia ion was loaded by ion exchange.After chemical reduction,the Ag NPs were anchored in situ on the frame of TIO film.The Ag nanoparticles prepared by this method can be fully exposed on the surface of the film and adhere firmly to the TIO film.By controlling the amount of silver ammonia ion and chemical reduction rate,the spacing,particle size and distribution of Ag NPs can be usefully regulated,and the matters of non-repeatability and instability in the utilization of noble metal materials are usefully avoided,which has great advantages in practical application.The prepared TIOAg SERS substrate was used to detect paraquat,diquat,paraquat free radical,diquat free radical,L-cysteine,pyrene,crystal violet,malachite green,melamine and rhodamine 6G,respectively.The detection limit was as low as 10^-10 mol/L.In the nanostructure of TIOAg,the photocatalytic activity of LSPR is enhanced with the space charge separation and transfer from TiO₂to Ag.The concentrations of paraquat,diquat,paraquat free radical and diquat free radical decreased gradually with the increase of time to 65.5%、64.8%、81.0%and 70.4%,respectively.Finally,silver nanoparticles were synthesized by Lee-Meisel method,and BSA was added to form Ag@BSA core-shell structure.Combined with SEM,TEM and UV-vis,it was found that BSA was effectively wrapped in the outer layer of silver nanoparticles and had good monodispersity.The detection ability of Ag@BSA SERS substrate for paraquat,diquat,paraquat and diquat free radicals was 10^-6 mol/L.When the concentration of paraquat and diquat is as low as this concentration,their characteristic peaks appear simultaneously in SERS spectra,which can be qualitatively analyzed.In this thesis,combined with SERS theory and LSPR mechanism,three kinds of nano silver SERS substrates were constructed,which were SiO₂@Ag nanoparticles,TIOAg films and Ag@BSA core-shell structures.by calculating the optimal configuration,exploring the theoretical spectrum and optimizing the experimental scheme,the trace detection of 10 target analytes such as bipyridine herbicides was realized.