Nitrogen-doped carbon dots for sensitive detection of ferric ions and monohydrogen phosphate by the naked eye and imaging in living cells

Nitrogen doped carbon dots (N-CDs) have been prepared via a one-pot hydrothermal method by using formamide and o -phenylenediamine as the carbon precursors. The as-fabricated N-CDs display excellent water dispersibility, good biocompatibility and anti-photobleaching properties. A strong emission band with an emission maximum ( λ fl max ) of 556 nm is observed under 450 nm excitation, and a large Stokes shift of 106 nm is presented. However, the fluorescence is quenched by the addition of Fe 3+ ; a good linearity is shown in the range of 0-65 μM with a detection limit as low as 0.85 μM. Fortunately, the quenched fluorescence could be recovered rapidly by the addition of monohydrogen phosphate (HPO 4 2− ) due to the formation of the stable [N-CDs-Fe 3+ -HPO 4 2− ] complex, and a good linearity is exhibited in the range of 0-60 μM with a low detection limit of 0.80 μM for HPO 4 2− . A novel "on-off-on" fluorescence response is seen with an obvious color change from yellow-crimson-yellow by the naked eye. In addition, the confocal microscopy images suggest that the as-synthesized N-CDs could serve as a sensitive nanosensor for Fe 3+ and HPO 4 2− detection, implying the diverse potential application of N-CDs in the biomedical field. Nitrogen doped carbon dots (N-CDs) have been prepared via a one-pot hydrothermal method by using formamide and o -phenylenediamine as the carbon precursors for Fe 3+ and HPO 4 2− detection.