Triple-channel SPR ion-imprinted fiber sensor enabled by MoS ₂ thickness-tuned resonance for multiplexed heavy metal ion detection

The distinction of multiple heavy metal ions (Cu²⁺, Ni²⁺, Pb²⁺) in water using surface plasmon resonance (SPR) is inherently challenging due to their nearly identical impact on the bulk refractive index. We demonstrate a novel triple-channel SPR fiber sensor that overcomes this limitation. The sensor leverages controlled MoS₂ film thickness (0, 20, 30 nm) to precisely tune and physically separate the SPR resonance wavelengths into distinct bands (600-650 nm, 750-800 nm, 900-950 nm) within the same aqueous medium (RI ≈ 1.333). Combined with ion-imprinted chitosan layers providing target-specific recognition, the sensor enables simultaneous, label-free detection. It achieves high sensitivities (e.g., 0.15 nm/(µmol/L) for Cu²⁺) and rapid response (<40 s) and incorporates a dedicated temperature probe for crosstalk compensation.