Multi-resonant Ag–AZO based PCF-SPR sensor for highly sensitive ethylene glycol detection in industrial applications

Abstract A dual-plasmonic Surface Plasmon Resonance (SPR) based Photonic Crystal Fiber (PCF) sensor incorporating silver (Ag) and aluminum-doped zinc oxide (AZO) layers is proposed for high-precision detection of ethylene glycol (EG) concentration. The PCF structure, designed using the Finite Element Method (FEM) in COMSOL Multiphysics, employs two plasmonic materials that generate multiple confinement-loss peaks, enabling enhanced detection over a broad spectral range. The novelty of the proposed configuration lies in exploiting the distinct plasmonic dispersion characteristics of Ag and AZO within a single PCF platform to support multiple spectrally separated resonance modes, including AZO-dominated, Ag-dominated, and hybrid Ag–AZO resonances. EG concentration is quantified through its corresponding refractive index variation, allowing accurate monitoring across 0–80% EG by weight. The sensor achieves an ultra-high wavelength sensitivity of 117,300 nm/RIU, an amplitude sensitivity of 2339 RIU −1 , a detection resolution of 8.53 × 10 −7 RIU, along with excellent linearity of 0.99808. A high figure of merit of 690 RIU −1 further confirms the superior detection sharpness enabled by the Ag–AZO dual-layer design. Owing to its compact geometry, multi-resonant response, and high sensitivity, the proposed SPR-PCF sensor shows promising performance for precise EG concentration monitoring in industrial and pharmaceutical applications where accurate concentration control is required.