A new Ni(II) nanostructured chelating system (DHN) was introduced for selective optical heavy-metal ion sensing in an aqueous medium. The cooperative chelating system comprising 8-hydroxyquinoline (8-HQ) and dimethylglyoxime (DMG) has been developed for the first time in association with fibre optic sensing for selective optical heavy-metal ion sensing in an aqueous medium. The Ni(II) nanocompound fluoresces upon 578 nm excitation, showing a highly sensitive optical response with a linear calibration curve in the range 0–100 ng/mL. The regression equation of the calibration curve is y = 0.0035x + 0.9990, which indicates very good linearity, implying R2 = 0.999 with high sensitivity (calibration slope of 0.0035) and low baseline noise (blank standard deviate on σ = 0.0002). The limit of detection (S/N = 3) is 0.17 ng/mL, whereas the limit of quantification is 0.57 ng/mL, which is much better compared to the reported conventional methods. The RSD is 0.020%, indicating high repeatability and signal stability. The fibre-optic chelating system shows quick optical response and steady signal transmission, so this sensing method is applicable for real-time determinations. XRD, TGA, AFM, and FESEM results prove the nanometric behaviour of Ni(II) DHN, which also contributes to analyte surface interaction and diffusion, providing enhanced calibration sensitivity and method robustness.
