A universal facile synthesis of nitrogen and sulfur co-doped carbon dots from cellulose-based biowaste for fluorescent detection of Fe3+ ions and intracellular bioimaging.

Carbon dots (CDs), especially heteroatom doped CDs derived from natural resources, have attracted growing interest due to their multiple potential applications. In this work, nitrogen and sulfur co-doped CDs (N/S-CDs) with a high quantum yield of 13.3% were synthesized by a facile approach based on one-step combustion treatment of cellulose-based biowaste of willow catkin. Due to the existence of urea and sulfuric acid used in the combustion process, the generated yield of the obtained N/S-CDs was raised to be as high as 14.3%. N/S-CDs were characterized by high-resolution TEM, FT-IR spectroscopy, XPS spectroscopy and Raman spectroscopy. The formation mechanism of N/S-CDs was also explored. These N/S-CDs with an average diameter of 7.3 nm demonstrated superior photo-stability, low cytotoxicity, pH stability and could be used for selective and sensitive detection of Fe3+ ions. Furthermore, based on their favorable feature of excellent biocompatibility and Fe3+ ions detection capability, the use of such N/S-CDs for intracellular Fe3+ ions detection application was also demonstrated.