Fabrication Of 3D SERS Substrate And Its Application In Detection Of Prohibited Pigments

Surface enhanced Raman spectroscopy?SERS?is an emerging analysis technology based on ordinary Raman spectroscopy,which relies on SERS active metallic nanoparticles to enhance conventional Raman signals.SERS has gradually developed into an ultrasensitive and non-destructive spectroscopic characterization technique,which has been importantly used in food safety inspection,environmental monitoring and pesticide residue detection.According to relevant theoretical research,the tremendous signal enhancement is arriving from the local electric field enhancement on metal nanostructures,which is called SERS substrates.Thus,for ultrasensitive quantitative SERS analysis,fabrication of high performance SERS substrates with good reproducibility is of great importance.In this paper,the highly sensitive three-dimensional?3D?Au@Ag nanocubes?NCs?SERS substrate has been fabricated by in situ ultraviolet?UV?Ozone cleaning and layer-by-layer self-assembly.The main research contents are as follows:Firstly,the Au@Ag NCs were employed as the building blocks to assembly into a large-area monolayer film using the liquid-liquid interface self-assembly technology.The Au@Ag NCs monolayer film was then treated by UV ozone post cleaning and in situ cleaning.The Au@Ag NCs two-dimensional?2D?SERS substrate was studied systematically by TEM,SEM,XRD,UV-vis,Raman spectroscopy,Image J software and FDTD simulation software.The nanogaps density and the interparticles spacing were also characterized as a function of in situ cleaning time.It was found that the UV ozone in situ cleaning technology could ensure a uniform and dense arrangement of nanoparticles on the substrates,which enables to achieve a higher Raman enhancement and better signal uniformity than the conventional post cleaned substrates.Based on the FDTD simulation,the electromagnetic filed distribution of Au@Ag NCs dimer with different interparticle distance were theoretically simulated.Such results agree remarkably well with the experimental results.Secondly,combining in situ cleaning,layer-by-layer self-assembly technology is used to prepare 3D SERS substrates with high sensitivity and excellent signal uniformity.The SERS sensitivity is further optimized by layer-by-layer assembly based on the optimized in situ cleaning monolayer films.The experimental results indicated that the in situ cleaning 3D SERS substrate showed several times-fold signal increase compared to the 2D SERS substrate,which also with a better signal uniformity and time stability.As last,based on the advantage of this 3D structure,the rapid detectiont of different kinds of carbonated beverages solution spiked with different concentrations of Rhodamine B?RB?and chrysoidine was successfully carried out.And the standard curve for quantitative detection of the two pigment molecules in three different carbonated beverages were established.The limit of detection for RB in the colorless and red carbonated drinks both could reach to 2.5×10^-7 M,and the limit of detection for chrysoidine in the colorless and orange carbonated drinks could reach to 10^-7 M and 2.5×10^-7 M respectively.And there is an excellent linear relationship between pigments molecule characteristic peak intensity and analytes concentration.The good liner relationship further confirms the high sensitivity and prominent uniformity of the 3D Au@Ag NCs substrates,which can greatly advance the application of SERS as a conventional analytical technique to detect various contaminants in food.