Metal–Dielectric Hybrid Dimer Nanoantenna: Coupling between Surface Plasmons and Dielectric Resonances for Fluorescence Enhancement

Abstract

Dimers made of noble metal particles possess extraordinary field enhancements but suffer from large dissipation, whereas low-loss dielectric dimers are limited by relatively weak optical confinement. Hybrid systems could take advantages from both worlds. In this contribution, we study the mode coupling in a hybrid dimer with rigorous dipole−dipole interaction theory and explore its potential in fluorescence enhancement. We first discovered that the direct coupling between metal surface−plasmon resonance and dielectric electric−dipole mode creates a hybridized mode due to the strong electric−electric dipole−dipole interaction between the constituent nanoparticles, whereas the dielectric magnetic−dipole mode can only indirectly couple to the plasmons on the basis of the induced electric−magnetic dipole−dipole interaction. When an electric/magnetic quantum emitter couples to the hybrid dimer, the emitter selectively excites the electric/magnetic (magnetic/electric) resonant modes of the dimer for emitter orientation parallel (perpendicular) to the dimer axis. Our study shows that the hybrid dimer simultaneously possesses high field enhancement and low-loss features, which demonstrates a fluorescence excitation rate 40% higher than that of the pure dielectric dimer and an average quantum yield 30% higher than that of the pure metallic dimer. On top of that, the unique asymmetrical structure of the hybrid dimer directs 20% more radiation toward the dielectric side, hence improving the directivity of the dimer as an antenna.

Cooperative surface‐enhanced Raman spectroscopy enhancement in Au nanorod/SiO2 nanoparticle solutions

“…These results suggest that electric dipoles of SiO 2 NPs interact with surface plasmon of AuNRs and SiO 2 NP themselves. [51] The surface plasmon-dielectric dipole interaction between AuNRs and SiO 2 NPs was further supported by the red-shift of surface plasmon peaks of AuNRs when SiO 2 NPs were added to AuNRs dispersion ( Figure S4). In this case, the red-shift of both transversal and longitudinal peaks suggests that the surface plasmon peak shift was not simply by aggregation of nanorods.…”

“…It is notable that the dipolar electric fields were enhanced between two SiO 2 NPs pairs even they were apart several hundred nanometers (Figure c). These results suggest that electric dipoles of SiO 2 NPs interact with surface plasmon of AuNRs and SiO 2 NP themselves . The surface plasmon‐dielectric dipole interaction between AuNRs and SiO 2 NPs was further supported by the red‐shift of surface plasmon peaks of AuNRs when SiO 2 NPs were added to AuNRs dispersion (Figure S4).…”

“…In this case, unlike metal nanoparticles forming only electric dipoles, dielectric nanoparticles form both electric and magnetic dipole resonances due to low field loss in the particles . When metal nanoparticles are suspended together with dielectric nanoparticles, it is expected that surface plasmon of metal nanoparticles and electric dipoles of dielectric nanoparticles are simultaneously generated upon exposure of light, and they can interact and create hybridized resonance mode by strong dipole–dipole coupling . Same as the case of dipole–dipole coupling between metal nanoparticles, dielectric‐metal dipole coupling leads to strong enhancement of electric field .…”

“…[47][48][49] When metal nanoparticles are suspended together with dielectric nanoparticles, it is expected that surface plasmon of metal nanoparticles and electric dipoles of dielectric nanoparticles are simultaneously generated upon exposure of light, and they can interact and create hybridized resonance mode by strong dipole-dipole coupling. [50][51][52] Same as the case of dipole-dipole coupling between metal nanoparticles, dielectric-metal dipole coupling leads to strong enhancement of electric field. [50][51][52] Moreover, it is also expected that large exclusion volume of dielectric nanoparticles confines analytes nearby metal nanoparticles and increase their local concentration.…”

“…[50][51][52] Same as the case of dipole-dipole coupling between metal nanoparticles, dielectric-metal dipole coupling leads to strong enhancement of electric field. [50][51][52] Moreover, it is also expected that large exclusion volume of dielectric nanoparticles confines analytes nearby metal nanoparticles and increase their local concentration. In this context, SERS enhancement in solution by addition of dielectric/metal nanoparticle ensemble has been investigated using model system consisting of SiO 2 NPs as dielectric nanoparticles, AuNRs as metal nanorods, and rhodamine 6G (R6G) and crystal violet (CV) as analyte molecules.…”