Green preparation of carbon quantum dots with wolfberry as on-off-on nanosensors for the detection of Fe and l-ascorbic acid.

A green and facile hydrothermal synthesis approach is proposed for the preparation of nitrogen-doped carbon quantum dots (N-CQDs) with wolfberry. These N-CQDs were developed as a highly sensitive fluorescent 'on-off-on' switch sensor for the sensing of Fe and l-ascorbic acid (AA). The N-CQDs displayed superior fluorescence characteristics of CQDs with a quantum yield up to 22%. The N-CQDs were demonstrated to selectively react with Fe, leading to fluorescence quenching effect, which was successfully used for the detection of Fe with a limit of detection at 3 μmoL•L. The addition of AA is supposed to repair the surface defects, and result in the fluorescence recovery. Based on this effect, the strategy of 'on-off-on' detection of AA was established with a limit of detection at 1.8 μmoL•L. Furthermore, the practical application of the detection of Fe lake water and AA in medical tablet was demonstrated, promising an effective and efficient 'on-off-on' nanosensor with low-cost, green synthesis for Fe and AA detection.