A U-shaped microfiber ring laser sensor for ultrasensitive detection of Ni2+ ions

As a common heavy metal pollutant, Ni2+ necessitates a rapid, sensitive, and accurate detection method to mitigate its impact on human health and the environment. This study developed a U-shaped single mode-tapered four core-single mode (STFS) based fiber ring laser (FRL) sensor coated with Ni2+ ion-imprinted chitosan (Ni2+-II-CS) for Ni2+ detection. Experimental results demonstrate that the average spectral stability in deionized water is 0.016 nm over 60 min. The detection time for Ni2+ is less than 8 min, with a limit of detection (LoD) as low as 1 nM. The proposed U-shaped STFS-based FRL sensors also show good selectivity, displaying limited cross-reactivity to other common heavy metal ions, including Cu2+, Cr2+, Pb2+, and Cd2+. Additionally, the analytical findings from pond and tap water specimens demonstrate wavelength shifts of −23.30 % and −27.06 %, respectively, when compared with measurements in deionized water. These findings indicate that the proposed microfiber sensor may have potential applications in heavy metal ion detection and environmental monitoring.