A Temperature Self-Compensated Dual-Channel SPR Fiber Sensor With Ion-Imprinted Polymers for Simultaneous Detection of Cu 2+ and Ni 2+

The simultaneous and specific detection of multiple heavy metal ions in complex environments remains a significant challenge for optical fiber sensors, primarily due to spectral crosstalk and temperature interference. To address this, we present a monolithically-integrated, dual-channel surface plasmon resonance (SPR) fiber sensor capable of crosstalk-compensated and temperature-compensated detection of Cu²⁺ and Ni²⁺. The sensor is fabricated by cascading two sensing regions on a single microstructured optical fiber (MOF), where a strategic combination of heterogeneous metallic films—a silver film for the Cu²⁺ channel and a gold film for the Ni²⁺ channel—creates two spectrally distinct resonance dips in the visible range. To overcome the limitation of specificity, ion-imprinted polymers (polyacrylic acid and chitosan) are functionalized onto the respective channels, creating highly selective recognition sites. Furthermore, an independent temperature-sensing probe, with its resonance strategically located in the near-infrared region, is incorporated into the optical path for real-time temperature monitoring, effectively eliminating thermal cross-sensitivity. Experimental results demonstrate that the sensor exhibits high sensitivity (up to 0.41 nm/μM for Cu²⁺ and 0.34 nm/μM for Ni²⁺ in the low concentration regime), a fast response time (20-30 s), and low detection limits. This work provides a compact and robust all-in-one sensing solution that paves the way for practical, multi-analyte environmental monitoring.