<p>Iron regulates redox processes and maintains cellular functions. In this study, a CDs@AuNCs-based ratiometric fluorescence probe was established for selective visual recognition and quantitative analysis of Fe²⁺. The probe combines blue-emitting carbon dots (CDs) and red-emitting gold nanoclusters (AuNCs), generating dual fluorescence emissions with distinct peaks at 435&#xa0;nm and 610&#xa0;nm. The I₆₁₀/I₄₃₅ ratio was optimized for Fe²⁺ detection, achieving excellent sensitivity with a detection limit as low as 3.5&#xa0;nM. The proposed probe demonstrated superior photostability, high environmental tolerance, and remarkable selectivity towards Fe²⁺ over other metal ions and small molecules. Real sample analysis, including ferrous succinate tablets, environmental water, and juice, showed satisfactory recoveries and low RSDs, confirming the reliability and accuracy of the method. CDs@AuNCs ratiometric probe is a promising tool for practical applications in clinical diagnostics, pharmaceutical quality control, and environmental monitoring, offering advantages such as simplicity, rapid response, and cost-effectiveness for Fe²⁺ ion detection in complex real samples.</p> Graphical Abstract <p></p>