<p> A&#xa0;novel fluorescence/colorimetric dual-mode detection strategy for uranium ions (UO₂²⁺) is presented&#xa0;based on a cerium-sulfonyl calix[4]arene (SC4A) platform. The exo- and endo-rim sites of SC4A can coordinate with Ce³⁺ and Ce⁴⁺ ions, respectively, quenching Ce³⁺ fluorescence and influencing the oxidase-like activity of Ce⁴⁺. In the absence of UO₂²⁺, the solution of 3,3,5,5-tetramethylbenzidine (TMB) remains blue, but upon UO₂²⁺ binding, Ce³⁺ dissociates from SC4A, restoring fluorescence, while UO₂²⁺ interacts with oxTMB, turning the solution from blue to colorless. This dual-mode system provides a linear fluorescence detection range of 30–800&#xa0;nM with a detection limit of 20.20&#xa0;nM, and a colorimetric range of 30–800&#xa0;nM with a detection limit of 27.78&#xa0;nM. By combining high-sensitivity fluorescence with visual colorimetric analysis, the proposed method possesses high sensitivity, accuracy, and reliability. Notably, smartphone-based color capture facilitates rapid and convenient sample analysis, enabling straightforward quantification at varying UO₂²⁺ concentrations. The method has been successfully applied to real water and urine samples, demonstrating its practical utility in environmental and biological monitoring of UO₂²⁺.</p> Graphical abstract <p></p>