The Fabrication Of AgNR SERS Substrates By Glancing Angle Deposition And Its Application In Food Safety Control

Surface-enhanced Raman scattering(SERS)is a popular technology for environmental monitoring,biological detection and food safety control.The key point of this technique is the fabrication of highly active substrates.In this manuscript,the different nanostructures were designed and fabricated by oblique angle deposition(OAD)and glancing angle deposition(GLAD)technology.The best SERS substrate was determined and used for food additives detection.In addition,a combination of ultra-thin layer chromatography(UTLC)and SERS technology was developed for the rapid separation and detection of the mixture dyes.The specific research contents are as follows.(1)The controllable and repeatable OAD/GLAD technique were used to fabricate nanostructures.The physical mechanism and enhancement effect of silver nanostructure were determined.The results showed that the AgNR array substrate with a tilted angle of 86°and a length of 2000 nm has the best SERS response.Its repeatability of single batch and multiple batch are less than 8%and 11%,respectively.The SERS enhancement factor of the AgNR array substrate was higher than 10~8.Moreover,the hot spot distribution of folding structure was simulated by Finite-Difference Time-Domain(FDTD),which presented the SERS hotspots were mainly distributed at the bottom and corner of the structure.The local surface electric field enhancement reached the strongest when the folding number is 3.(2)The sensitivity and repeatable AgNR array substrates were applied to the SERS detection of food additives.The theoretical Raman spectra of the molecules were determined based on density functional theory(DFT),and their characteristic peaks and the corresponding vibration assignments were confirmed.This SERS based method showed that the limit of detection(LOD)of saccharin sodium was 1 mg/L.The quantitative detection of saccharin sodium could be realized from four different soft drinks by one step liquid-liquid extraction.SERS spectra of six dyes were obtained and the LOD were determined(0.05 mg/L~5 mg/L).Moreover,the allura red was quantitatively detected by AgNR array in different candies with the simple pretreatment.(3)The obtained SERS substrate was used as the stationary phase in UTLC to separate and detect mixed dyes.The results showed that the R_f values were suitable for these dyes when using methanol as the mobile phases.The background signal of methanol was weak,and the R_f values of the six dyes in the ordinary UTLC were different(0.21<R_f<0.71).The strongest SERS signal of the dyes located at the specific position on AgNR substrate.The separation and detection of mixed dyes of sunset yellow and amaranth were reached.Furthermore,the rotating UTLC separation process were performed to accelerate the separation process.The results showed that all kinds of dyes were flake in a fan-shaped region.The rotating UTLC presented that it reached the ultra-high speed separation and detection of four kinds of mixed dyes.This research provides an idea for the fabrication of high performance SERS substrate by OAD/GLAD technique.It can contribute information to the combination of SERS and other pretreatment techniques.