ZrO2@Ag@SiO2 Sandwich Structure with High SERS Enhancement Effect and Stability

The spectroscopy of surface-enhanced Raman scattering (SERS), with its high sensitivity and specific chemical fingerprinting, has received increasing attention. A stable substrate is extraordinarily important for the trace detection of the SERS technique, but the challenge of SERS substrate production with high stability and uniformity still imposes the unavoidable barriers. In this paper, we design a multilayer core–shell-nanostructured ZrO2@Ag@SiO2 nanoparticle through liquid extraction. First, we regulated the usage of AgNO3 (1 wt %) to obtain Ag@SiO2 which is silver coated with uniform distribution; on the surface of silica, the number of silver particles is abundant. Then, we discussed the influence when different concentrations of zirconium propoxide are added on the zirconia layer's thickness. Then, we applied FDTD simulation to explain the position of SERS "hotpots" with and without ZrO2 coating. We have found that the detection capability of ZrO2@Ag@SiO2 can be up to 10–9 M for 4-ATP; with ZrO2@Ag@SiO2 SERS substrates exposed to the atmospheric environment for up to 30 days, we could still obtain the excellent SERS signal performance contributed by the good chemical stability of ZrO2, when ZrO2 is coated on the surface of Ag@SiO2, the zirconia layer formed has a protective role . These experimental results have indicated that the outer zirconia layer could prevent the silver surface from being oxidized, ensuring its stability , which is quite crucial for the applied SERS.