Carbon Dot- and Curcumin Dye-Based Dual-Emission Fluorescence Ratiometric Probes for Rapid Smartphone Detection of Brilliant Blue in Food

Brilliant blue (BB), a synthetic food additive widely employed in commercial food products, such as beverages and confectioneries, has raised health concerns due to potential risks associated with prolonged consumption and excessive intake. This necessitates the development of rapid analytical methods for BB monitoring in food matrices. Herein, we present a ratiometric fluorescent probe system integrating red-emitting carbon dots (R-CDs) with curcumin (Cur) for sensitive BB detection. The R-CDs were synthesized through a hydrothermal method using phosphoric acid and <i>o</i>-phenylenediamine as precursors. In this design, the R-CDs function as the responsive signal element, while Cur serves as an internal reference due to its exceptional photostability. The proposed sensing platform demonstrates BB concentration-dependent fluorescence quenching of R-CDs through a dual mechanism involving the inner filter effect and static quenching interactions. A linear correlation (<i>R</i>² = 0.996) was established between the fluorescence intensity ratio (F₅₆₅/F₆₂₄) and BB concentrations ranging from 0 to 5.5 μM, achieving a detection limit of 67.78 nM. The practical applicability of probe was validated through successful BB quantification in commercial beverages and fruit juices, showing recovery rates of 97–109%. Notably, we developed a portable smartphone-assisted detection platform utilizing RGB color analysis, enabling real-time onsite visual monitoring. This ratiometric fluorescence strategy combining R-CDs and Cur establishes a reliable analytical approach characterized by enhanced accuracy, precision, and anti-interference capability compared with single-signal detection systems, demonstrating significant potential for food safety applications.