Synthesis of N,S co-doped carbon quantum dots-metal complex for the detection of fluoride (F⁻) ion in adults and Children's toothpastes

We herein report a simple and facile synthesis of N, S co-doped carbon quantum dots (N,S-CQDs) complexed with lead ions as a fluorescent nanoprobe for the detection of fluoride ions in adults’ and children’s toothpaste. The nanoprobe was prepared via a hydrothermal method using sodium sulphide, glutamine and citric acid as the sulphur, nitrogen and carbon precursors, respectively. The structural characterisation of the as-synthesised nanoprobe confirmed that the material is small, crystalline and spherical. The nanoprobe was sensitive and selective towards Pb²⁺ in the presence of other metal ions. In addition, the as-prepared nanoprobe/Pb²⁺ complex was sensitive and selective towards fluoride ions in the presence of other ions, with a detection limit of 78.03 nM. Furthermore, the as-synthesised material served as a nanoprobe for the detection of fluoride ions in commercial toothpaste with recoveries of 98.32–117.03 % in adult’s toothpaste and 103.24–111.88 % in kids’ toothpaste with RSD< 5 %, indicating its potential application in complex matrices.