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

Abstract

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 ZrO 2 @Ag@SiO 2 nanoparticle through liquid extraction. First, we regulated the usage of AgNO 3 (1 wt %) to obtain Ag@SiO 2 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 ZrO 2 coating. We have found that the detection capability of ZrO 2 @Ag@SiO 2 can be up to 10 −9 M for 4-ATP; with ZrO 2 @Ag@SiO 2 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 ZrO 2 , when ZrO 2 is coated on the surface of Ag@SiO 2 , 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.

Ag@MIL-101(Cr) Film Substrate with High SERS Enhancement Effect and Uniformity

“…Thus, the detection capability of the Ag@MIL-101(Cr) film substrate was up to 10 −11 M. The characteristic Raman peaks of 4-ATP were clearly visible and consistent with previous reports. 38,39 There are four major peaks at 1077, 1141, 1390, and 1434 cm −1 in the Raman peaks of 4-ATP, which have posed a multivariate computation problem and increased the difficulty of calculation. Thus, to ensure the calculation accuracy and simplicity, we have adopted the principal component analysis (PCA) method 40 to reduce dimension numbers of those multivariate variables, and credibility could be ensured.…”

Trends in Application of SERS Substrates beyond Ag and Au, and Their Role in Bioanalysis

“…For example, Xu et al achieved a 3-fold higher SERS signal with a superhydrophobic substrate based on a silver nanoparticle coated zinc oxide nanorods array (Ag@ZnO) than that on the ordinary hydrophilic Ag@ZnO substrate due to the superhydrophobic condensation effect [ 252 ]. Another research carried out by Shi et al fabricated multilayer core−shell-nanostructured ZrO 2 @Ag@SiO 2 nanoparticles through liquid extraction for the detection of 4-aminothiophenol (4-ATP) and rhodamine 6G (R6G) at 785 nm excitation and demonstrated that zirconia film protects the silver nanoparticles from aggregation, improving the stability of the substrate [ 190 ]. The list of 11 studies for SERS non-noble metal substrates other than Al and Cu (e.g., Fe 3 O 4 @Au nanoshells, CoFe 2 O 4 @HNTs/AuNPs, Au-ZnO NRs, Au semishells on TiO 2 spheres, etc.)…”

“…The list of 11 studies for SERS non-noble metal substrates other than Al and Cu (e.g., Fe 3 O 4 @Au nanoshells, CoFe 2 O 4 @HNTs/AuNPs, Au-ZnO NRs, Au semishells on TiO 2 spheres, etc.) are summarized in Table 4 [ 182 , 183 , 185 , 186 , 187 , 188 , 189 , 190 , 191 , 252 ].…”

Versatile Graphene‐Isolated AuAg‐Nanocrystal for Multiphase Analysis and Multimodal Cellular Raman Imaging†

“…Hence, it is highly non‐trivial to confine Ag NCs in a stable nanospace for protecting them from complex environments, and meanwhile, avoiding the direct contact with analytes. Recently, Ag@SiO 2 [ 30 ] and SiO 2 @Ag@TiO 2 [ 31 ] core‐shell NCs have been prepared to confine the Ag NCs in a nanospace of chemically inert SiO 2 or TiO 2 shell for avoiding the direct contact between Ag core and analytes, further achieving reliable SERS detection of several biomolecules. However, these core‐shell NCs may suffer from harsh conditions like extremely acidic and high‐salt solutions.…”