Improved dual-band refractive index sensing based on gap plasmon

Resonant plasmonic nanostructures have attracted much attention due to their exotic optical properties. In this work, we numerically investigate single- and dual-gap ring structures, respectively, and they can be used for refractive index sensing by exciting the gap plasmon mode with sharp resonance spectra. The dual-gap ring plasmonic sensor shows the dual-channel properties and the corresponding sensitivities are 513 nm/RIU and 809 nm/RIU with the refractive indices range of 1.32-1.37, respectively. Furthermore, the gap ring structures are highly symmetrical, and have advantages in fabrication and pave the way for advanced optical devices to detect bio-molecules.