Phosphatase-like Ce⁴⁺@UiO-66-NH₂ nanozyme-based dual-mode hydrogel nanosensor for visual detection of paraoxon

The highly selective and sensitive detection of paraoxon residues at low environmental concentrations remains challenging. Herein, a novel fluorescent metal-organic framework composite (Ce⁴⁺@UiO-66-NH₂) with excellent phosphatase-like activity was developed to catalyze the hydrolysis of paraoxon into yellow p-nitrophenol (p-NP), which quenched the composite's blue fluorescence via the inner filter effect. Based on this mechanism, a simple, portable, non-biological colorimetric/fluorescent hydrogel nanosensor (CM-SA spheres) was constructed by incorporating red fluorescent Mn-CDs with aggregation-induced emission as an internal reference. Upon increasing paraoxon concentration, the spheres showed visible color changes from colorless to yellow under daylight and blue to red under UV light. The sensor demonstrated a visual detection sensitivity of 0.05 μg mL^-1 and limits of detection of 0.013 μg mL^-1 (daylight) and 0.027 μg mL^-1 (UV). In real sample analyses of tea and water, the CM-SA spheres exhibited strong anti-interference capability and reliability, offering a practical strategy for paraoxon degradation and detection.