Electrochemical Sensor Based on Polydopamine-Coated Silver Nanowire/Defect-Ridden UiO-66-NH ₂ Nanocomposites for Trace Detection of Cd(II) and Pb(II) Ions in Water

Due to growing environmental and health concerns associated with toxic heavy metal ion (HMI) pollution, it becomes necessary to develop fast, highly sensitive, and selective detection methods. Herein, an electrochemical sensor based on a glassy carbon electrode (GCE) modified with a thin film of polydopamine-coated silver nanowire (AgNW@PDA)/defect-ridden UiO-66-NH2 (AgNW@PDA/UiO-66-NH2) nanocomposites was developed for trace detection of cadmium (Cd(II)) and lead (Pb(II)) ions in water. The electrochemical performance of the proposed AgNW@PDAt/UiO-66-NH2/GCE sensor was then optimized by varying the polymerization time (t) of dopamine on the AgNWs. Compared to defect-ridden UiO-66-NH2, AgNW@PDAt/UiO-66-NH2 nanocomposites offered a higher electrochemically active surface area, a better standard heterogeneous electron transfer rate constant, and enhanced sensing performances. The AgNW@PDA24/UiO-66-NH2 nanocomposite (t = 24 h) showed the best electrochemical properties and was further utilized for both individual and simultaneous detection of HMIs using differential pulse voltammetry (DPV). The optimized AgNW@PDA24/UiO-66-NH2/GCE sensor achieved a low limit of detection (LOD) of 25.2 nM for Cd(II) and 9.8 nM for Pb(II), and high sensitivity of 7.18 and 18.2 μA μM–1 cm–2, along with a wide linear range of 0.05–1.1 and 0.05–0.7 μM, respectively, for individual detection. The AgNW@PDA24/UiO-66-NH2/GCE exhibited a higher selectivity for Pb(II) ions in the presence of other interfering metal ions, depicting a recovery rate of ∼97–100% over other HMIs. The sensor further demonstrated good stability, repeatability, and reproducibility. The practical applicability of the developed sensor was also confirmed by the successful detection of Cd(II) and Pb(II) ions in spiked tap water samples. Finally, a paper-based flexible sensor was fabricated using the optimized AgNW@PDA24/UiO-66-NH2 ink, yielding a linear range of 5–60 μM and LOD values of 81 and 153 nM for Pb(II) and Cd(II) ions, respectively, thus confirming its potential for on-site monitoring of HMIs in real water samples.