Plasmonic Nanoantenna: Enhanced Near-Field Focusing with Branched Gold Dual-Rim Nanorings

In this study, we present the synthesis of novel branched nanoparticles characterized by inner dual-rims and outer protruded branches. Platinum dual-rim nanorings served as the initial templates, and a series of multistep synthetic procedures were employed with the aid of l-glutathione acting as a branch-inducing capping agent. The resulting Au dual-rim nanorings with branches demonstrated an electromagnetic near-field focusing capability, which was attributed to the formation of circular intrananogaps between the inner and outer rims, along with protruded tips that facilitate light energy collection and transfer to the inner nanogaps. This configuration led to a more pronounced enhancement of near-field focusing compared to the analogous Au dual-rim nanorings lacking branches. The synergistic effect arising from both branches and inner nanogaps in the branched Au dual-rim nanorings enables robust single-particle surface-enhanced Raman scattering measurement, which is unattainable using the analogous monorim, or noninner gap-based nanoring, architecture. We believe that our synthetic approach to fabricating branched Au dual-rim nanorings offers valuable insights into particle design strategies where plasmonic field enhancement holds significance.