Fiber SPR Sensor Based on S-Taper Sensitivity Enhancement for Nickel Ion Detection

The heavy metal ions in food usually exist in the form of mixtures and have low concentrations. It is crucial for human health to achieve highly sensitive and specific detection of heavy metal ions in food. In this article, we propose a fiber surface plasmon resonance (SPR) sensor that adjusts sensitivity by adjusting the incident angle through fiber microstructure and uses it for the specific detection of heavy metal nickel ions. By fabricating an S-taper microstructure on a single-mode fiber, adjusting its axial offset and taper area diameter, the sensitivity of the sensor was increased from 2294.50 to 3244.62 nm/RIU. By modifying double-stranded DNA on the surface of the sensing region of the fiber S-taper structure, specific recognition of heavy metal nickel ions was achieved, with a detection sensitivity of 3.587 nm/[lg (mg/mL)] and a detection limit as low as 8.65 pg/mL. The sensitivity of the sensor for detecting other heavy metal ions is lower than 0.44 nm/(lg (mg/mL)). The sensitization specific fiber SPR sensor proposed in this article provides a new solution for the highly sensitive and specific detection of various heavy metal ions in food.