Preparation of high-quality biocompatible carbon dots by extraction, with new thoughts on the luminescence mechanisms.

Recently, carbon dots (CDs) have been among the most promising emerging fluorescent labels for cellular imaging. In this work, a new facile synthesis method was developed for fabricating CDs from polystyrene foam waste and common organic solvents. The CDs obtained have tunable emission from blue to orange and are expected to be of use for labeling different cellular structures simultaneously. Transmission electron microscopy, x-ray diffraction, Raman spectra, Fourier transform infrared spectrometry, UV-vis, and fluorescence spectrophotometry (PL) were employed to investigate the structures and luminescence properties of CDs. The highest quantum yield (QY) achieved was 36%. The mechanisms for the formation and luminescence of the CDs are analyzed. The ability of the solvent to disperse the CDs plays a very important role in the origin of PL. The type of organic solvent has an important influence on the position of emission peaks and the QY. Different emissive traps play the dominant role in the luminescence of carbon materials. Furthermore, a hemolysis assay was performed to evaluate the biocompatibility of these CDs in vitro. The biocompatibility of the CDs, even at very high doses, ensures their potential in biomedical applications.