Complex Plasmonic Hot Nanocavity: Vertically Nested Au Quintuple Nanorings Produce a Strong Cavity-Enhanced Near-Field Focus.

Abstract

Herein, we report plasmonic quintuple nanorings (QNRs) featuring geometrically complex internal nanocavities within a single entity that was synthesized through a rationally designed six-step wet-chemical process. This architecture consists of two vertically stacked dual-rim nanorings surrounding a central monorim nanoring, forming nested layers with multiple inner spaces. These structurally intricate nanocavities generate an ensemble of internal hot zones and maximize near-field focusing along all optical planes nested within a single entity (<i>x</i>, <i>y</i>, <i>z</i> axes), which we refer to as plasmonic hot cavities. To verify the electromagnetic field enhancement within these hot nanocavities, we measured the single-particle surface-enhanced Raman scattering (spSERS) of the individual Au QNRs. The high density of hot zones distributed throughout the internal nanocavities enables this pseudo-two-dimensional (2D) plasmonic nanostructure to exhibit exceptionally strong spSERS signals, driven by the combined effects of conventional SERS and cavity-induced enhancement. This marks a compelling demonstration of a "nanocavity"-driven scattering phenomenon distinct from traditional surface-enhanced optical effects. The cavity-enhanced Raman scattering (CERS) effect offers a strategy for designing complex plasmonic nanocavities for advanced CERS-based analysis and applications.