Turn-on fluorescent assay based on nitrogen-doped carbon dots and aptamer for low-background detection of kanamycin

This study presents a low-background "turn-on" fluorescent assay for sensitive trace kanamycin (KANA) detection. Nitrogen-doped carbon dots (N-CDs) efficiently quench ∼80% of the fluorescence of the FAM-labeled KANA Aptamer (F-APT) via electrostatic adsorption, establishing a stable, low-fluorescence baseline. Upon binding KANA, F-APT folds into a stable hairpin structure, drastically reducing its affinity for N-CDs and fully restoring FAM fluorescence. The assay offers a linear range of 5-200 nmol/L and a limit of detection (LOD) of 1.67 nmol/L (S/N = 3). For real samples, honey and milk require only centrifugation and dilution, yielding spike recoveries of 89.9-108.7%. Critically, the method is enzyme-free, separation-free, instrumentally simple, and highly selective against common coexisting antibiotics- demonstrating reliability and practical utility for trace KANA detection in food.