A ratiometric electrochemical sensor based on the intrinsic Ce4+/Ce3+ redox couple of Ce-UiO-66 for sensitive mercury ion detection

Cts/Ce-UiO-66 was developed for sensitive ratiometric detection of Hg 2+ . • Intrinsic Ce 4+ /Ce 3+ redox couple in MOF provides a stable reference signal. • Chitosan coating promotes Hg 2+ enrichment and stabilizes the modified film. • The sensor showed a 3.73 nM LOD and 95.0%–105.3% recovery in pond water. Mercury pollution remains a serious environmental concern because of its toxicity, persistence, and bioaccumulation in aquatic environments. Herein, a ratiometric electrochemical sensor for Hg 2+ detection was developed using a chitosan/Ce-UiO-66 (Cts/Ce-UiO-66) composite. Ce-UiO-66 was used as a redox-active sensing scaffold. Its porous framework may provide accessible interfacial sites that may contribute to Hg 2+ accumulation, while the intrinsic Ce 4+ /Ce 3+ redox response provides a built-in electrochemical signal for internal normalization under controlled measurement conditions. Chitosan was introduced as a film-forming matrix. The amino and hydroxyl groups of chitosan may contribute to Hg 2+ interfacial preconcentration, while the polymer matrix improves the stability of the modified film. The integration of the proposed Cts-assisted Hg 2+ interfacial accumulation and the intrinsic Ce-related normalization signal enabled ratiometric Hg 2+ quantification. Under optimized differential pulse voltammetry conditions, the sensor exhibited a linear response toward Hg 2+ over the concentration range of 0.10–3.00 μM, with a limit of detection of 3.73 nM. The sensor was further evaluated in a fish-pond water sample, achieving recoveries of 95.00–105.33% at the tested spiking levels. These results support the preliminary feasibility of the Cts/Ce-UiO-66-based ratiometric sensor for Hg 2+ determination in the tested fish-pond water matrix under the present experimental conditions. Scheme 1. Schematic illustration of the preparation and sensing processes of Cts/Ce-UiO-66/GCE. Download: Download high-res image (108KB) Download: Download full-size image