In this article, we prepare the nitrogen (N) and sulphur (S) co-doped carbon dots (NS-CDs) via a one-step hydrothermal method using the methionine as the precursor. The N and S doping content reach as high as 15.2 at.% and 19.5 at.%, separately. The analysis of the photoluminescence dates exhibits that the relationship between the excitation and the corresponding emission wavelength can be summarized as a linear fitting function. In addition, the as prepared NS-CDs also exhibits sensitive detection properties for heavy metal cations. With these excellent characteristics, there are extensive potential applications for NS-CDs in industry and environmental monitoring.

PEG-passivation enhanced the luminescence intensity of nitrogen-doped carbon dots markedly.