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

Abstract

Nitrogen doped carbon dots (N-CDs) have been preparedviaa one-pot hydrothermal method by using formamide ando-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 (λflmax) 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 Fe3+; 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 (HPO42−) due to the formation of the stable [N-CDs-Fe3+-HPO42−] complex, and a good linearity is exhibited in the range of 0-60 μM with a low detection limit of 0.80 μM for HPO42−. 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 Fe3+and HPO42−detection, implying the diverse potential application of N-CDs in the biomedical field.