Pinhole-Containing, Subnanometer-Thick Al2O3 Shell-Coated Ag Nanorods as Practical Substrates for Quantitative Surface-Enhanced Raman Scattering

Successful employment of surface-enhanced Raman scattering (SERS) as a powerful means for trace analyte detection depends greatly on the nanostructures of noble metals as substrates, which to date are not able to satisfy the many prerequisites for quantitative SERS analysis, e.g., excellent SERS sensitivity, long-term SERS stability in air, chemical inertness, corrosion resistivity, superior reproducibility, good chemisorption of target molecules, and so forth. We report here that Ag nanorods coated with a subnanometer-thick, pinhole-containing Al2O3 shell (Ag NRs@Al2O3) could serve as such a substrate that meets most of the above requirements. Because of the coverage of ultrathin Al2O3 shell, the Ag NRs@Al2O3 substrate exhibited superior SERS sensitivity and was able to work for a long time in very corrosive and harsh environments. Meanwhile, with the Al2O3 pinholes contained, this specially designed coreshell nanostructure was capable of quantifying a variety of molecules at trace levels, i.e., those that can be adsorbed chemically on the surface of either Ag or Al2O3 or both. This study provides a simple approach to prepare highly sensitive, corrosion resistive, and chemically inert SERS substrates for practical, quantitative SERS analysis with wide detection fields.