<p> A&#xa0;hydrogel test kit is presented&#xa0;that integrates a metal–organic framework (MOF)-based nanoprobe for portable fluoride ion (F⁻) detection. This nanoprobe, denoted as ThT@UiO-66/Ru(bpy)₃²⁺ (TUR), is fabricated by encapsulating thioflavin T (ThT) within a zirconium-based MOF (UiO-66), followed by adsorption of Ru(bpy)₃²⁺ onto its surface. The confinement effect of UiO-66 restricts the conformational rotation of ThT, resulting in intense green fluorescence from ThT@UiO-66. Together with the red emission from Ru(bpy)₃²⁺, the TUR exhibits typical dual-emission characteristics. However, ThT@UiO-66 is highly sensitive to F⁻, which disrupts the&#xa0;UiO-66 structure and quenches the fluorescence of ThT@UiO-66, while the fluorescence of Ru(bpy)₃²⁺ remains unaffected. This distinct fluorescence response enables ratiometric detection of F⁻, achieving a detection limit as low as 2.9&#xa0;μM. The successful quantification of F⁻ in milk samples demonstrates the applicability of the hydrogel test kit in complex biological matrices. Moreover, the incorporation of a smartphone as a signal readout device facilitates on-site quantitative detection, providing operational simplicity, portability, and cost-effectiveness. These features highlight the potential of the hydrogel test kit for point-of-care applications in food safety monitoring.</p> Graphical Abstract <p></p>