A sensitive sensor based on carbon dots for the determination of Fe³⁺ and ascorbic acid in foods

To develop a feasible, sensitive, and essential sensor is important for the identification of Fe³⁺ ions and ascorbic acid (AA). Herein, highly fluorescent heteroatom co-doped carbon dots (N,S-CDs) with a quantum yield (QY) of 24.6% were synthesized, using hydrothermal treatment of L-cysteine (Cys) and 1-amino-2-naphthol-4-sulfonic acid (ANSA). The fluorescence emission of the as-prepared N,S-CDs was quenched strongly by Fe³⁺ ions, and this was further recovered by the reduction effect of AA on Fe³⁺. Based on this, continuous fluorescence sensing of Fe³⁺ and AA with an "on-off-on" style was developed. The detection of Fe³⁺ and AA were in relatively wider linear ranges of 5.00-105 μmol L^-1 and 4.97-54.8 μmol L^-1, with a detection limit of 0.10 μmol L^-1 and 2.4 nmol L^-1 (S/N = 3), respectively. Then, the N,S-CDs were successfully used to measure Fe³⁺ ions and AA in some daily food samples, and this method exhibited some advantages over most other reported techniques in the term of response speed, quantum yield, and detection limit.