Nitrogen-doped carbon dots by means of a simple room-temperature synthesis using BSA protein and nucleosides or amino acids

There is considerable interest in the synthesis and applications of carbon dots due to their intriguing tunable optical properties, among which are strong photobleaching resistance and low toxicity for biomedical applications in sensing and biosensing. C-dots are prepared using different fabrication methods that use carbon-rich materials, including carbohydrates, citric acid, proteins, plants and organic waste materials. In this work, we report the synthesis of nitrogen co-doped carbon dots, which is carried out through a simple and quick method at room temperature, with serum bovine albumin as the carbon source, and an amino acid (L-Arginine) or a nucleoside (Adenosine, Cytidine) to be added during the synthesis as the nitrogen source and then crosslinked to surface carbon dots by glutaraldehyde. After twenty hours of synthesis, the solution turned orange, indicating the complete formation of highly stable fluorescent C-dots, characterized by UV−Vis, fluorescence, FTIR, XPS spectroscopies and SEM. The resulting C-dots were all fluorescents, with a mean size of 5 nm, exhibiting the following functional groups on the C-dots surface: CN, NH, CN and CO, confirming the co-doping with nitrogen. Among the prepared samples, the addition of Cytidine yields the strongest emissive colloid, showing a robust yellow fluorescence (maximum emission at 560 nm), with a high quantum yield of 31.4% and good photobleaching resistance to green laser (117 mW/cm2).