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Fabrication of SERS-active Au@Au@Ag double shell nanoparticles for low-abundance pigment detection

Au@Au@Ag double shell nanoparticles were fabricated and characterized using TEM, STEM-mapping and UV-Vis methods. Using crystal violet as Raman probe, the surface-enhanced Raman scattering (SERS) activity of the as-prepared Au@Au@Ag nanoparticles was studied by comparing to Au, Au@Ag and Au@Au core-shell nanoparticles which were prepared by the same methods. Moreover, it can be found that the SERS activity was enhanced obviously by introduction of NaCl and the concentrations of NaCl played a key role in SERS detection. With an appropriate concentration of NaCl, the limit of detection as low as 10−10 mol/L crystal violet can be achieved. The possible enhanced mechanism was also discussed. Furthermore, with simple sample pretreatment, the detection limit of 5 µg/g Rhodamine B (RhB) in chili powders can be achieved. The results highlight the potential utility of Au@Au@Ag for detection of illegal food additives with low concentrations.