A highly selective fluorescent sensor for manganese(II) ion detection based on N,S-doped carbon dots triggered by manganese oxide

A highly selective, carbon dots (CDs)-based fluorescent sensor for manganese(II) ions (Mn2+) was proposed. The synthesis of N,S-doped CDs (N,S-CDs) involved simple pyrolysis of a mixture of lactose and l-cysteine in a hot NaOH solution. The as-synthesized codoped CDs exhibited a weak fluorescent emission peak at 510 nm when excited at 430 nm. In the presence of Mn2+, the intensity of the fluorescence signals was effectively increased with a small redshift in the spectrum. Thus, by tracing the degree of fluorescence enhancement, the material could be used as a selective probe for Mn2+ detection. The possible sensing mechanism was based on the oxidation of the N,S-CDs by MnO2, which was generated from mixing Mn2+ with NaOH in the N,S-CDs-containing medium. A linear relationship was established between the extent of the increase in fluorescence and the increasing Mn2+ concentration from 0 to 5.0 μM with a limit of detection (LOD) of 0.12 μM. Remarkably, even in the presence of other cations, the developed sensor remained highly selective toward Mn2+. The feasibility of our developed sensor in real applications was confirmed with environmental samples, showing excellent accuracy and precision.