Nanoporous Gold Stacked Layers as Substrates for SERS Detection in Liquids or Gases with Ultralow Detection Limits and Long-Term Stability

Surface-enhanced Raman scattering (SERS) substrates consisting of stacked ultrathin nanoporous gold layers are used to detect very low concentrations of molecules in liquids or gases. The SERS substrates are obtained by copper chemical etching of alternative copper and gold stacked nanolayers. This process is a reliable method for fabricating uniform and reproducible SERS substrates, with a robust SERS response at extremely low detection limits. By optimizing fabrication conditions combined with a thorough analysis of the SERS mappings and using 2,2-bipyridine (BP) as probe molecules, the detection threshold corresponding to a detectable SERS response reaches a BP concentration of 10-18 mol center dot L-1 in water. An additional Raman mechanism is also highlighted by mu-surface enhancement spatially offset Raman spectroscopy (mu-SESORS): gold ligaments, inside nanoporous layers, act as waveguides for the incident light, leading to a significant increase in the size of the active SERS area. Moreover, these SERS substrates could be stored for several days without a significant decrease in their properties, and they can be reactivated and reused after SERS analysis. The ability to detect low BP vapor pressure is also demonstrated.