Local dielectric environment-dependent plasmonic optical sensitivity of gold nanocage: from nanobox to nanoframe

In this study, a gold nanobox with 40 nm edge length has been transformed into nanoframe gradually by increasing the square-hole length in each {100} facet of the hexahedron. The local dielectric environment-dependent plasmon spectra and refractive index sensitivity of this face-holed single gold nanocage were investigated based on the discrete dipole approximation method. Both the redshift of the resonance peak position and the sensitivity factor increased near exponentially with increasing hole length, which could be attributed to the changing of hot regions of plasmonic field coupling. Moreover, the shift of their resonance peak position to the refractive index of environmental medium increased linearly, and the face-holed nanocage-based sensor shows an excellent sensitivity factor of 955.7 nm/RIU [figure of merit (FOM) = 3.58]. It was also noticed that the non-monotonic transform of the local field enhancement factor (|E/E ₀ |) with a maximum of 80.9 is also extremely affected by the refractive index. The physical mechanism discussed herein may be that the polarized field in local dielectric environment becomes intense as the refractive index increases, resulting in an improvement of field enhancement factor on the corners. We therefore believe that the square-hole length of {100} facets could enhance the plasmonic optical sensitivity of nanocage-based nanoparticles.