Astaxanthin-derived multielement carbon quantum dots for selective fluorescence sensing of chlortetracycline through...

Antibiotic contamination in aquatic environments is an increasing concern because persistent residues can affect ecosystems and human health. Here, we describe astaxanthin-derived, multielement-doped carbon quantum dots (B-CQDs) as fluorescent probes for chlortetracycline (CTC). The B-CQDs were prepared by a one-step hydrothermal method using astaxanthin and sulfanilamide as co-precursors, and were characterized by XRD, FT-IR, XPS, UV-visible absorption spectroscopy and fluorescence spectroscopy. The resulting dots showed blue emission, a quantum yield of 13.6%, and stable fluorescence under changes in pH, ionic strength, temperature, storage and ultraviolet irradiation. The fluorescence response was selective for CTC among the tested antibiotics, amino acids and metal ions, with a linear range of 0.25-0.60 mM and a limit of detection of 4.66 μM. Spectral analysis indicated that quenching was dominated by the inner filter effect, with surface-defect-mediated non-radiative pathways probably contributing to the response. Spiked water samples gave recoveries of 102.73-105.79% in distilled water and 100.29-109.72% in tap water, with relative standard deviations below 1.31%. These results support the use of astaxanthin-derived B-CQDs as a simple fluorescent platform for CTC monitoring in aqueous samples.