3D Connected Plasmonic Octamers for Boosting Single-Particle Surface-Enhanced Raman Scattering

Three-dimensional (3D) complex plasmonic intragap nanostructures (PINs) have attracted significant attention in the field of surface-enhanced Raman scattering (SERS) owing to their abundance of interior gaps and voids, which enable robust near-field focusing. However, developing a simple, precise, and reproducible synthetic strategy remains a great challenge, as the preparation of such complex nanostructures often demands multiple laborious synthetic steps with controlled chemistry. Here, we present a facile one-pot approach for synthesizing 3D complex PINs, termed connected plasmonic octamers (CPOs), consisting of eight nanoparticles arranged in a cubic configuration and interconnected with metal bridges. The synthesis involves the selective etching of Ag nanocubes (NCs) followed by galvanic replacement between the etched Ag NCs and a Au precursor. Through adjustment of the etching time, the vertex and edge sites are selectively etched, resulting in the rounding of the produced Ag NCs and providing precise control over the structural parameters of CPOs. This configuration enables robust near-field focusing at the vertices, edges, and intragap region, as confirmed by both single-particle SERS measurements and theoretical simulations. Our study represents a significant advancement toward the facile yet precise synthesis of 3D complex PINs, holding great promise for applications in biosensing and optical devices.