Vertically Coupled Hybrid Metasurfaces for Multimodal and Tunable Plasmonic Sensing

Abstract

A hybrid plasmonic metasurface is presented, consisting of vertically coupled silver nanodisc (AgND) arrays and aligned gold nanowire (AuNW) substrates, offering multifunctional and tunable optical sensing capabilities. The metasurface is fabricated through a microsphere-assisted deposition and etching strategy, yielding highly ordered nanostructures with strong vertical field confinement. Simulated and experimental reflectance spectra confirm that the hybrid architecture supports multiple localized surface plasmon resonance (LSPR) modes—absent in the individual components—originating from enhanced near-field coupling between the AgNDs and AuNWs. A comprehensive analysis reveals that geometric parameters such as nanodisc radius and nanowire height significantly affect the spectral response and field distribution. The sensor achieves a maximum refractive index (RI) sensitivity of 611.47 nm/RIU and a humidity sensitivity of 0.858 nm/%RH when coated with a polyvinyl alcohol (PVA) layer. Furthermore, dynamic spectral tuning is realized by selectively etching the alumina template to modulate the effective refractive index of the supporting substrate. Integration onto an optical fiber tip demonstrates the device's suitability for compact, remote, and layered sensing platforms. This study introduces a versatile and scalable strategy for designing high-performance plasmonic sensors applicable to environmental monitoring and biochemical detection.