A nitrogen-doped triple-excitation red carbon dots-based dual-analytes ratiometric fluorescence probe for the detection of malachite green and rifampicin in aquatic organisms.

A ratiometric fluorescence probe founded on the triple-excitation of red carbon dots (R-CDs) is developed for the simultaneous detection and discrimination of malachite green (MG) and rifampicin (RIF) for the first time. The R-CDs are fabricated through a solvothermal method utilizing citric acid and biuret as precursors, displaying fluorescence excitation wavelengths at 472 nm, 498 nm and 536 nm, with an emission wavelength at 610 nm. Encouraged by triple-excitation property of R-CDs, the presence of MG induces a more pronounced decline at the 536-nm excitation peak of R-CDs compared to the peaks at 498 nm and 472 nm due to fluorescence resonance energy transfer and static quenching effect. For RIF detection, the inner filter effect causes a dramatic decline in fluorescence intensities at 472 nm and 498 nm, while the 536 nm peak declines more slowly. Furthermore, according to differential quenching responses of R-CDs to MG and RIF, linear discriminant analysis and hierarchical cluster analysis are employed to discriminate MG and RIF in mixtures. Besides, a smartphone-assisted sensing platform is developed to enable visual detection of MG and RIF, showing satisfactory recoveries in aquatic samples. Overall, our work provides an innovative ratiometric strategy for simultaneous detection of MG and RIF, which holds significant potential for applications in food security and ecological surveillance.