Independent Dual-Mode Humidity and Hydrogen Detection Using a Plasmonic-Photonic Hybrid Metasurface

High-sensitivity multitype detections independent of the metadevices are essential in industrial process control, environmental monitoring, biomedical diagnosis, etc. Here, we report a plasmonic-photonic hybrid metasurface (PPHM), consisting of a poly(vinyl alcohol) (PVA) guided-mode resonator sandwiched between a top palladium (Pd) grating array and a bottom gold reflector, achieving dual-mode optical detections independent of humidity and hydrogen simultaneously. The humidity properties in hydrogen gas or air were determined by the guided mode from a dielectric resonator with the PVA gratings and a spacer. The volume expansion in a PVA layer at high humidity gives rise to the redshift of the guided mode for the PPHM. An RH sensitivity of 0.31 nm/RH was achieved with a humidity range of 30–80%. The hydrogen-sensing characteristics of a PPHM result from the phase change of palladium after hydrogen absorption, which then causes reflectivity variations. The relative reflection change of a PPHM was up to 1.12 as palladium gratings were fully hydrogenated. The results suggest that the PPHM is a promising platform for realizing multitype optical detections of humidity and hydrogen sensing.