High Sensitivity Localized Surface Plasmon Resonance Sensing Using a Double Split NanoRing Cavity

Practical implementations of biosensing with metallic nanostructures often suffer from the large line width of the plasmon resonances induced by large radiative damping. A double split nanoring cavity is designed to suppress the radiative damping. The coupling between the superradiant quadrupole mode of a split nanoring with one gap and the subradiant quadrupole mode of a split nanoring with two gaps leads to splitting of the modal energies into bonding and antibonding quadrupole–quadrupole modes. The radiative damping is suppressed effectively, leading to a narrow line width for both bonding and antibonding quadrupole–quadrupole modes. Calculation results show that bulk refractive index sensitivities exceeding 1200 nm/RIU with a figure of merit exceeding 8.5 in the near-infrared are obtained with a Au double split nanoring cavity. The large cavity volumes and uniform electric fields inside the cavity make the double split nanoring cavity a good platform for surface-enhanced molecular sensing.