V ₂ O ₅ /rGO Nanohybrid-Coated Fiber Optic Sensor for Subppb Detection of Nickel Ions

Nickel ion (Ni 2+ ) contamination in water poses significant environmental and health risks, necessitating the development of sensitive and selective detection methods. In this work, we present an optical fiber sensor coated with a vanadium pentoxide−reduced graphene oxide (V 2 O 5 −rGO) nanohybrid for the detection of Ni 2+ ions in aqueous solutions in the range of 1−10k ppb. The nanohybrid was synthesized via a facile sol−gel approach, characterized using XRD, HRSEM, and UV−vis spectroscopy, and deposited ex situ over salinized U-bent fiber optic sensor (U-FOS) probes. The optical absorbance response of the sensor at a 450 nm wavelength was monitored to quantify the Ni 2+ concentration in the aqueous samples. The developed sensor exhibited high sensitivity, rapid response time, and excellent selectivity toward Ni 2+ ions, even in the presence of competing metal ions at 1:50 ppm. These sensors manifest a LOD and LOQ down to 0.24 and 0.812 ppb, respectively. Subsequently, a portable and sensitive 12-channel U-FOS probe array device employed for Ni 2+ detection demonstrated a 0.1 ppb detection limit. The sensor was challenged with filtered sewage treatment plant effluents (neat and spiked with different Ni 2+ concentrations in ppb), which yielded a recovery rate of 96% to 104% when benchmarked with the standard ICP-MS analysis. These results demonstrate the potential of V 2 O 5 −rGO U-FOS for real-world water quality monitoring. This study paves the way for further exploration of advanced materials for the detection of many other metal ions by exploiting the U-FOS platform.