Synthesis And Application Of Functional SERS Substrates Based On Raspberry-like Gold

Food safety is related to people's livelihood.It has always been a key area of concern for the country and the people.However,the traditional detection methods are cumbersome,costly,and time-consuming,and cannot meet the growing demand for detection.A simple,low-cost and convenient detection method is urgently needed for the market.Surface-enhanced Raman spectroscopy(SERS)detection technology has the above characteristics.Whereas,the current functional SERS substrates are generally poor compatibility with portable Raman spectrometers,low detection sensitivity for water-insoluble molecules,and weak recognition ability to multi-component in complex environments.In this paper,raspberry-like gold(R-Au)with rough surface and partially hollow structure was prepared to match with the portable Raman spectrometer in which Ag nanoparticle was used as the core.4-mercaptopyridine(4-MPY)as the internal standard was modified with R-Au through coordination and a thin layer of mesoporous Si O₂ was coated on R-Au in order to adsorb water-insoluble molecules.Then,the quantitative SERS detection of water-insoluble molecules was realized.The R-Au@Si O₂@Ag composite substrate was constructed by loading Ag nanoparticles on the surface of Si O₂.The strong electric field effect was formed by its double resonance structure and the identification and detection of mixed components in complex environments were realized.The specific research contents are as follows:(1)R-Au with rough surface and partial hollow structure was synthesized by a two-step method.The controllable adjustment of the R-Au plasmon wavelength can be achieved by changing the addition amount of chloroauric acid.Because of its unique morphology and structure,it still retains a strong SERS"hot spot"with the increase of the plasmon wavelength.Therefore,it matched well with a portable Raman spectrometer with an excitation light wavelength of 785 nm.As a result,the detection sensitivity to the probe molecules crystal violet(CV)and malachite green(MG)is 100higher than using ordinary gold(N-Au)nanoparticles as substrates.Through simple pretreatment of duck meat,R-Au was used for the SERS simulation detection of furan antibiotics in duck meat.The results showed that the SERS detection limits of nitrofurantoin and nitrofurazone were both 0.05 mg/L,and the linear relationship was0.05 mg/L with good linear relationship(R²>0.99)and high recovery(98.1%-105.6%).R-Au can be used in the market to detect drug residues of antibiotics in food rapidly.(2)The surface of R-Au was coated with a layer of mesoporous Si O₂ by the Stober method.The optimal material ratio of ammonia water and Tetraethoxysilane(TEOS)was determined by the control variable method and characterization analysis,and the thickness of the Si O₂ shell layer was 10-14 nm by adjusting the stirring time.Using the coordination effect between R-Au and-SH,4-MPY was modified in situ to form an internal standard.Water-insoluble molecules were"retained"within the SERS hot spots formed by R-Au because of the mesoporous Si O₂.The correction for environmental changes and the quantitative detection of water-insoluble molecules CCl₄ and deltamethrin pesticide molecules were realized.Compared with R-Au,the detection sensitivity was increased by 10 times;compared with the R-Au@Si O₂ substrate without internal standard,the correlation coefficient of deltamethrin were increased from 0.824to 0.975.The R-Au@Si O₂ substrate with internal standard provides the possibility for the quantitative detection of water-insoluble pesticides.(3)Using the surface template activation method,R-Au@Si O₂@Ag with double resonance structure was constructed by supporting Ag NPs on the Si O₂ shell of R-Au@Si O₂.The SERS performances were verified by detecting CV,paraquat,and deltamethrin.Compared with R-Au@Si O₂,the detection limit of CV was increased from 10^-9 M to 10^-10 M,the detection limit of paraquat was increased from 10^-8 M to10^-10 M,and the detection limit of deltamethrin was improved was increased from 10^-9M to 10^-10 M.Paraquat and deltamethrin showed a good linear relationship with R² of0.9875 and 0.9797,respectively.Finally,the simulated SERS detection of apple juice shows that R-Au@Si O₂@Ag can effectively distinguish the mixed pesticides of paraquat and deltamethrin in apple juice.the R² of the two pesticides are 0.8851 and0.9191 with good linear relationship,respectively.Research indicates that the R-Au@Si O₂@Ag substrate can be used fast detection in multi-component and complex environments in the field of food safety.