Highly-sensitivity copper(II) ion detection via optical fiber Mach-Zehnder interferometer modified with ZIF-67/ι-carrageenan/sucrose

This paper proposes an optical fiber Mach-Zehnder interferometer (MZI) sensor based on a ZIF-67/ι-carrageenan/sucrose, achieving high sensitivity and low detection limit of copper ion (Cu 2+ ) detection. Among them, ZIF-67 has the advantages of high specific surface area and easy synthesis, providing abundant binding sites on the optical fiber surface. The ι-carrageenan contains abundant sulfate groups, through which Cu 2+ are captured and bound by synergistic interactions with both sulfate groups and oxygen-containing functional groups. The ZIF-67 porous frameworks and ι-carrageenan/sucrose are synchronously integrated via an in-situ growth method at room temperature. As the concentration of Cu 2+ increases, the competitive binding between Cu 2+ and sucrose at functionalized residue sites triggers the dissociation of the relatively weak hydrogen bonds between ι-carrageenan and sucrose. Simultaneously, Cu 2+ forms stable complexes with ι-carrageenan and detaches from the optical fiber surface, thereby leading to changes in the surface refractive index and shifts in the interferometric spectral dip position to enable detection. Experiments indicate that the sensor exhibits a linear sensitivity of 11.23 nm/lgM in the range of 0–2 μM Cu 2+ concentration, with a calculated detection limit of 26.88 nM. The sensor achieves a rapid response within 60 s and exhibits excellent selectivity and stability. Its high detection sensitivity, combined with an ambient-temperature fabrication process, provides a highly sensitive and cost-effective solution for precise Cu 2+ monitoring in environmental applications.