Eccentricity improved plasmon refractive index sensing and SERS performances of Au nano-donuts

The extraordinary electric-field enhancement within the inherent gap of Au nano-donuts promises their strong capability in surface enhanced Raman scattering (SERS) and plasmon refractive-index sensing. It is crucial to unveil the eccentricity effect on their localized surface plasmon resonance (LSPR) properties to access their optimized sensing and SERS performances. By finite element method, we demonstrate that elliptic-nano-donut monomers are able to provide improved refractive-index sensitivity (S), figure of merit (FOM), and SERS enhancement than that of concentric ones. The corresponding optimized values are revealed to reach 444.5 nm/RIU, 10.3RIU−1 and 6.25×106, respectively, which are superior than that of similar sized Au nanospheres and nanoholes. The effect of the electromagnetic coupling in between dimeric components on the improvement of S, FOM and SERS enhancement is also discussed. The obtained eccentricity dependent LSPR properties are not only fundamentally important, but also provide new clues for future developing efficient SERS and plasmon sensing substrates. •The eccentricity effect on the LSPR properties of Au nano-donut monomers is investigated numerically by FEM.•The EM mechanism for their eccentricity dependent response of dipolar LSPR mode is discussed.•Their maximum S (and G) reaches 444.5 nm/RIU (and 6.25×106).•Their EM coupling further improves their optimized S and SERS enhancement ∼1.2 and 3×103 fold, respectively.