Polyhedral-Au@SiO₂@Au Core–Shell Nanoparticle Reveals a Broadband and Tunable Strong Local Field Enhancement

In this paper, we introduce different polyhedral Au nanoparticles (AuNPs) as the core of Au@SiO2@Au and analyze the effect of internal nanogap morphology on local field enhancement. Compared with spherical Au core, polyhedral Au core has sharper edges and vertices, and it can make the plasmon resonance peaks of Au core and shell closer to each other by changing the internal polyhedron-shell nanogap morphology, so the polyhedral-Au@SiO2@Au nanoparticle can realize a broadband and tunable strong local electric field enhancement, especially for tetrahedral-Au@SiO2@Au and octahedral-Au@SiO2@Au nanoparticles. We numerically demonstrate that the polyhedral-Au@SiO2@Au nanoparticle can even produce a 100-200 nm broadband window and a 2-3 orders of magnitude stronger local electric field enhancement compared with the spherical-Au@SiO2@Au nanoparticle, which produces only a 50-60 nm narrow band. This polyhedral-Au@SiO2@Au core-shell nanoparticle is a promising plasmonic nanostructure for signal enhancement during excitation and radiation processes for enhanced fluorescence or Raman imaging, especially for multiwavelength Raman analysis of multiple reporter molecules whose signals need to be enhanced simultaneously.