Hydrangea-derived nitrogen-doped carbon dots: A dual-purpose platform for on-site chlortetracycline detection and time-limited anti-counterfeiting.

In this work, blue-emissive nitrogen-doped carbon dots (N-CDs) were prepared via a one-step hydrothermal method using Hydrangea macrophylla flowers as the carbon precursor and L-histidine as the nitrogen source, affording a quantum yield of 9.8%. The N-CDs emit bright blue fluorescence under 365 nm UV light but undergo self-quenching within 30 min. This "single-use luminescence" behavior is, to the best of our knowledge, exploited for anti-counterfeiting for the first time. When printed onto chiffon or cotton-linen textiles, the N-CDs generate non-toxic, washable, and non-reproducible "time-limited fluorescent identifiers." In addition, the N-CDs exhibit an instantaneous response to chlortetracycline (CTC), showing fluorescence quenching at concentrations as low as 0.105 μmol L within a linear range of 20-75 μmol L. The average recovery in rainwater samples approached 100%, outperforming most reported CD-based antibiotic probes. This study bridges two practical scenarios-environmental safety monitoring and wearable anti-counterfeiting-offering a green, low-cost, and scalable paradigm.