Smartphone-assisted ratiometric fluorescent sensor CQDs@Eu-MOF for the visualization and quantitative detection of Hg2+ and norfloxacin.

The precise monitoring of Hg2+ and norfloxacin (NOR) residues is essential for ensuring food safety and environmental health. This study describes the fabrication of a dual-emissive CQDs@Eu-UiO-66 hybrid, synthesized via the in-situ encapsulation of carbon quantum dots (CQDs) within a Eu3+-doped UiO-66 framework. By leveraging the blue emission of CQDs and the red emission of Eu3+, this ratiometric platform facilitates the ultrasensitive, discrete detection of Hg2+ and NOR, yielding LODs of 2.08 nM and 48.96 nM, respectively. Mechanistic investigations reveal that Hg2+ quenching proceeds via photoinduced electron transfer (PET), while NOR detection is driven by the inner filter effect (IFE) and electrostatic association. The sensor demonstrates high matrix resilience in complex samples, including lake water, milk, and chicken. Furthermore, integrating a smartphone-based RGB interface enables a transition toward portable, digitized on-site quantification. This platform aligns with regulatory standards, offering a robust solution for rapid food safety monitoring in resource-limited settings.