Designing and fabricating double resonance substrate with metallic nanoparticles-metallic grating coupling system for highly intensified surface-enhanced Raman spectroscopy

Recently, nanoparticle–film coupling systems in which metal nanoparticles (supported localized surface plasmons, LSPs) are separated from a flat metal film (supported surface plasmon polaritons, SPPs) by a spacer have been widely reported due to its strong local enhancement field. However, there is are limited studies, which employ the design of combing metal grating into the nanoparticle–film gap system. Here, we propose and fabricate a novel double-resonance SERS system by strategically assembling Au NPs separated by a MoO₃ nanospacer from an Ag grating film. The Ag grating with clear SPP effect is used for the first time in a double-resonance system, and the monolayer Au NPs array is well assembled onto the top of the Ag grating with a compact and uniform distribution (inter-particles gap of about 5 nm). As a result, we experimentally and theoretically demonstrate a significant near-field enhancement. The very strong near-field produced in the proposed SERS substrates is due to multiple couplings, including the Au NPs–Ag grating film coupling and Au NPs–Au NPs coupling. In addition, the as-proposed SERS substrates show good reproducibility of SERS, which have potential applications in plasmonic sensing and analytical science.