Nitrogen and sulfur co-doped highly luminescent carbon dots for sensitive detection of Cd (II) ions and living cell imaging applications.

In this work, we have developed a green, simple and fast one-pot microwave-assisted strategy for synthesis of nitrogen and sulfur co-doped fluorescent carbon dots (CDs) using scallion (SL) as the carbon source. Optical properties of the SL-CDs have been measured by UV-visible and fluorescent spectroscopy. The morphology of the prepared SL-CDs has been performed by transmission electron microscopy (TEM). Surface functionality and elemental composition of SL-CDs was analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra. The photoluminescent (PL) quantum yield of the obtained scallion carbon dots (SL-CDs) can reach as high as 18.6%. We further demonstrated that the SL-CDs can be used as fluorescent probes for detection of Cd2+ ions with a high sensitivity and an excellent selectivity. Linear relationships between the variation of the luminescent intensity of the SL-CDs before and after exposing the Cd2+ ions versus the concentration of Cd2+ ions in the range of 0.1-3.0 μM and 5.0-30.0 μM. The detection limit of Cd2+ ions can reach 15.0 nM. Moreover, the as-prepared SL-CDs exhibit negligible or extremely low cytotoxicity, which makes them be able to be used as fluorescent probes for living cell imaging. Overall, the prepared SL-CDs have promising applications in sensing of Cd2+ ions and in vivo or in vitro bioimaging.