Convenient synthesis of carbon nanodots for detecting Cr(VI) and ascorbic acid by fluorimetry

The plant Sophora flavescens Ait was used to prepare carbon nanodots (CDs) which exhibited high fluorescence quantum yield (35.2%). The CDs were remarkably quenched by chromium(VI) (Cr(VI)) and acted as an “on–off” fluorescent probe to realize the real sample detection of Cr(VI) at pH 6.0. The linear range was 0.06–40 μM and the detection limit was 20 nM. In addition, it was found that the fluorescence recovered again when Cr(VI) was redoxed by ascorbic acid (AA), and the recovery degree was linear with the amount of AA from 0.1 to 4.0 mM. With a low detection limit of 80 μM, the system was satisfactorily used to detect AA in several fruits. In conclusion, the proposed “on–off–on” fluorescent probes based on the synthesized CDs were simple, of low-cost and concise for the sequential detection of two targets.