Fano Resonances in Plasmonic Octamer Nanohole Array Using Finite-Difference Time-Domain Method for Sensing Application

The phenomenon of asymmetric Fano resonance supported by the plasmonic nanohole arrays has attracted considerable interest in ultrasensitive label-free biosensing in recent years. A unique plasmonic nanohole structure with excellent transmission efficiency and nanometer-level linewidth is required to enable sensitive and specific biosensing. A unit cell of a plasmonic octamer nanohole array enriched with multiple asymmetric spectral resonances is proposed in this work which is enriched in propagating and localized surface plasmon resonances (SPRs). The proposed nanohole array structure, electromagnetic field distribution, and sensitivity were quantitatively analyzed using the fully vectorial finite-difference time-domain (FDTD) method. The proposed structure has a figure of merit (FoM) of 148.29, and an extremely high bulk sensitivity (BS) of 436.8 nm/RIU for the analyte layer refractive index of 1.33–1.38. Our proposed octamer sensor also showed a surface sensitivity (SS) of 7.17 nm/nm for the detection of an immobilized DNA monolayer. The proposed octamer nanohole array has a nanometer-level spectral linewidth (SL) of 1.81 nm and more than 70% transmission at wavelengths between 600 and 1150 nm.