Sodium cellulose sulfate-derived nitrogen and sulfur co-doped carbon dots for the detection of tetracycline in white shrimp

The South American white shrimp, a predominant species in aquaculture, has raised concerns regarding food safety due to the detection of residual tetracycline in both water and shrimp tissues. In this study, nitrogen and sulfur co-doped carbon dots were synthesized for the first time using sodium cellulose sulfate as the precursor and ethylenediamine as the dopant, resulting in a high fluorescence quantum yield of 33.1%. The carbon dots were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The average size of the carbon dots was found to be 15.60 ± 2.15 nm, and their excellent photostability and thermal resistance were confirmed through a series of stability tests. The N,S-CDs demonstrated selective recognition of tetracycline, with a strong linear relationship between fluorescence quenching and tetracycline concentration (R² = 0.9967). The limit of detection was as low as 0.219 μM. Fluorescence lifetime analysis revealed that the quenching mechanism was attributed to the inner filter effect. When applied to white shrimp samples, the method showed promising results. Overall, nitrogen and sulfur co-doped carbon dots offer a sensitive, rapid, and simple approach for the detection of tetracycline in food safety testing.