Ultranarrow Linewidth Coupling Resonance in Flexible Plasmonic Nanopillar Array for Enhanced Biomolecule Detection

Abstract Plasmonic nanostructures, due to their extremely strong confinement and enhancement of optical field, have emerged as a potential tool in myriad applications, ranging from nano‐laser to surface‐enhanced Raman scattering (SERS) and biosensing. To break through the restriction of intrinsic losses and radiative damping in metal nanostructures resulting in broad plasmon resonance, a plasmonic nanostructure sensor employing hexagonal nanopillar array on flexible substrate to form the bilayer gold cap‐hole coupling structure is proposed and demonstrated. The sensor is fabricated by the combination of vacuum coating and template transfer, and experimentally exhibits an ultranarrow plasmon resonance coupling mode with a linewidth of 4.5 nm. Such a sharp linewidth resonance originates from the coupling of geometrical‐induced Wood's anomaly (WA) and Fabry–Perot (FP) modes. Benefiting from this ultranarrow resonance, a figure of merit (FOM) of 140.6 and spectroscopic detection noise down to 0.02 nm are demonstrated in the bulk refractive index (RI) sensing. Furthermore, the nanopillar array enables the detection of bovine serum albumin biomolecular with the detection limit of 0.27 µm. The plasmonic array device can be further investigated for more potential practical utility that are valuable and significant for label‐free biomolecular sensing with high sensitivity and high throughput.