Microwave-assisted synthesis, characterization, cell imaging of fluorescent carbon dots using L-asparagine as precursor

L-Asparagine, a common amino acid, is a cost-effective and ideal precursor for carbon dots because of its high nitrogen content and its abundance in nature. By using L-asparagine as a biocompatible precursor, fluorescent nitrogen-doped carbon dots (A-CDs) were prepared by a one-pot microwave-assisted method. Then, a reasonable structure for A-CDs was put forward, which confirmed that unconjugated small molecules could transform into carbon dots with the sp2 core, and was helpful in the discussion of the photoluminescence mechanism. It was concluded that the photoluminescence origin of A-CDs was from the graphite-like structure and surface defects. The A-CDs showed high stability in strong ionic solutions and negligible cytotoxicity even when the incubation concentration was up to 800 μg mL−1. Long-time bioimaging tests suggested that A-CDs have great potential for use in a wide variety of biological applications.