Twisted fiber SPR sensor for copper ion detection

A novel fiber surface plasmon resonance (SPR) sensor for the detection of copper ions was reported in this paper. The twisted region was fabricated on the single-mode fiber by using the fiber hot melt torsion technology, and the light transmitted in the core was coupled to the cladding. The cladding was coated with nano gold film, and the cladding mode totally reflected at the interface between the cladding and the gold film, which excited the SPR effect. After optimizing the fabrication parameters of the twisted region, the twisted fiber with a pitch of 123 µm was selected to construct the SPR sensor probe, and its refractive index sensitivity is 2689.06 nm/RIU. Furthermore, the self-assembled chitosan / polyacrylic acid film was immobilized on the surface of the sensor layer by layer, and the concentration of copper ion was detected. The test results indicate that with the increase of Cu2+ concentration from 15.7 nM to 1.57 mM, the SPR resonance valley moves towards the long wavelength direction, the detection sensitivity is 3.46 nm/lgC, and the limit of detection (LOD) is 10.10 nM. The proposed fiber SPR sensor is simple to manufacture, which provides a new idea for heavy metal ion detection by fiber sensor.