Realization of relaxed fabrication tolerances and on‑demand sensitivity in hybrid plasmonic‑photonic sensors

Hybrid plasmonic-photonic nanostructures hold significant promise for diverse applications spanning biosensing, environmental monitoring, pharmaceutical analysis, and optical devices. However, two core bottlenecks persist and impede their commercial use as sensors: the challenge of achieving relaxed fabrication tolerances and the inability to precisely control sensitivity. Herein, we demonstrate the designs and experimental realization of an array of hybrid plasmonic-photonic gratings (HPPG) exhibiting a relaxed fabrication tolerance (up to 60 nm for the grating width) and numerically demonstrating period-guided "on-demand" bulk sensitivity for the first-order Wood's anomaly (WA)-dominated mode, and experimentally supporting this characteristic at a structure period of 770 nm. These unique attributes primarily stem from a WA-dominated sensing mode coupled with Fabry-Pérot (FP) resonances. Further multipolar decomposition analysis reveals that relaxed fabrication tolerance correlates strongly with a stable scattering-intensity ratio between the two dominant multipolar modes: toroidal dipole and electric quadrupole. By leveraging the WA-FP coupled mode, the HPPG was validated as a label-free biosensor, achieving concentration sensitivities of 283 (nm·nL)/μg for hemoglobin and 140 (nm·nL)/μg for creatinine. These findings demonstrate the proof-of-concept potential of the HPPG as a foundational platform for future label-free biomedical sensing research.