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 (Cu 2+ , Ni 2+ , Pb 2+ ) 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 MoS 2 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 Cu 2+ ) and rapid response (<40 s) and incorporates a dedicated temperature probe for crosstalk compensation.