Palm charcoal-derived carbon dots as fluorescent nanosensors for metronidazole detection in poultry meat

Expired traditional Chinese medicine (TCM) palm charcoal was utilised as a carbon precursor for the green synthesis of fluorescent carbon dots (CDs) via a microwave-assisted approach, yielding CDs with an average diameter of 3.2 nm. The CDs demonstrated excellent dispersion stability in polar media, which is attributed to the abundance of oxygen-containing functional groups on their surface. The CDs exhibited strong fluorescence with maximum excitation and emission at 325 and 404 nm, respectively. The quantum yield (QY) was measured to be 9.7%. The CDs displayed robust stability, with their fluorescence intensity remaining largely unchanged across a wide pH range, under prolonged UV exposure, and in high-salt conditions. The CDs served as a highly selective fluorescent probe for metronidazole (MNZ), exhibiting significant fluorescence quenching. This sensor demonstrated a linear response range of 8.70–32.7 μM for MNZ quantification, with a detection limit of 0.696 μM. The predominant quenching mechanism of CDs was identified as an inner filter effect (IFE), accompanied by a small contribution of dynamic quenching. Furthermore, the practical applicability of the sensor was substantiated by spike-recovery assays in real samples, which yielded satisfactory recoveries of 99.64%–101.50%, thereby validating the method’s accuracy and reliability for MNZ detection.