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

To develop a feasible, sensitive, and essential sensor is important for the identification of Fe 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 Fe ions, and this was further recovered by the reduction effect of AA on Fe. Based on this, continuous fluorescence sensing of Fe and AA with an "on-off-on" style was developed. The detection of Fe and AA were in relatively wider linear ranges of 5.00-105 μmol L and 4.97-54.8 μmol L, with a detection limit of 0.10 μmol L and 2.4 nmol L (S/N = 3), respectively. Then, the N,S-CDs were successfully used to measure Fe 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.