Fluorescent sensing of Fe3+ and the pesticide coumaphos using biomass-derived lotus carbon dots via a “turn off-on” mechanism

A novel “turn off-on” fluorescence sensing platform was developed for the sequential detection of Fe 3+ and coumaphos pesticides using carbon dots derived from biomass lotus seeds (LS) and functionalized with monoethanolamine (MEA). The LS-MEA-CDs were synthesized via a one-step hydrothermal method, exhibiting strong blue fluorescence with an excitation and emission wavelength of 350 and 435 nm, respectively. Upon addition of Fe 3+ , the fluorescence was quenched, which was subsequently restored by coumaphos via competitive binding. The sensor showed linear responses for Fe 3+ (0.625–35 μg mL −1 , LOD = 0.021 μg mL −1 ) and coumaphos (12.5–150 μg L −1 , LOD = 1.54 μg L −1 ), with high selectivity against potential interferents. Practical application in vegetable samples yielded recoveries of 90.61–109.09%, confirming its accuracy and robustness. Overall, the proposed method provides a rapid and efficient tool for detecting coumaphos residues in environmental monitoring and food safety settings. • Green carbon dots were synthesized from lotus seeds by one-step hydrothermal method. • A turn off–on fluorescence sensor for Fe 3+ and coumaphos detection. • Low detection limits of 0.021 μg mL −1 and 1.54 μg L −1 for Fe 3+ and coumaphos. • Applied in vegetable samples with 90.61–109.09% recoveries.