Green synthesis of N-doped carbon quantum dots using Senecio scandens for Cu²⁺ sensing in tea sample

In this study, Nitrogen-doped carbon quantum dots (N-CQDs) were synthesized via a one-pot hydrothermal route using Senecio scandens as the carbon source and urea as the nitrogen dopant. The resulting N-CQDs are monodisperse and near-spherical, with an average diameter of 1.6 nm. It possess a partially graphitized core and abundant N/O-containing functional groups at the surface. The N-CQDs exhibits good photostability and disperses readily in water. Fluorescence quenching of the N-CQDs by copper ions follows a static photoluminescence mechanism. The response is linear over the range of 0-3 μmol/L, and the limit of detection is 0.646 μmol/L. The N-CQDs also display favorable biocompatibility which can be used for non-invasive fluorescence imaging of copper ions in live zebrafish larvae as well as in Arabidopsis thaliana roots. These results confirm the method is reliable for real tea sample analysis. Recoveries ranged from 95.64% to 102.44%, with relative standard deviations remaining below 4.79%. Overall, this study has established a practical sensing platform suitable for on-site Cu²⁺ monitoring in tea and other agricultural food products.