Target-oriented synthesis of yellow fluorescent nitrogen-doped carbon dots for intelligent and real-time visual detection of malachite green in fish

As a triphenylmethane dye, malachite green (MG) is strictly regulated in aquaculture by numerous countries due to its persistence and acute toxicity, posing significant risks to human health. This has driven the demand for rapid and sensitive detection methods for MG. Herein, we present a lateral flow test strips (LFTS)-based sensing platform utilizing yellow fluorescent nitrogen-doped carbon dots (N-CDs) for real-time visual detection of MG. N-CDs are synthesized via a solvothermal method using o-phenylenediamine and 4-aminostyrene as precursors, exhibiting strong yellow fluorescence. The presence of MG leads to fluorescence quenching of N-CDs through fluorescence resonance energy transfer (FRET) and inner filter effect (IFE), achieving a limit of detection (LOD) of 79 nM over a linear range of 0.079-40 μM. Additionally, a portable fluorescence sensing device is constructed by integrating the N-CDs, LFTS and smartphone-assisted RGB (red, green, blue) analysis enabling on-site visual detection of MG within a concentration range of 0.133-30 μM, with a LOD of 133 nM. Meanwhile, practical applications in fish tissue samples exhibit satisfactory recoveries ranging from 98.8 % to 105.6 %, with relative standard deviations (RSDs) below 2.72 %. These results suggest that this proposed LFTS platform exhibits high accuracy and reliability for MG detection in aquatic products. Therefore, this simple, cost-effective and on-site detection approach provides a promising strategy for ensuring food safety and safeguarding human health.