Microwave-assisted synthesis of luminescent and biocompatible lysine-based carbon quantum dots

[Display omitted] •CQDs showing strong fluorescence are simply prepared from lysine through microwave assisted pyrolysis.•Lysine-based CQDs are less than 10nm and have amorphous carbonic cores and amine and hydroxyl functionality in their surface.•The use of lysine as an AB2 type amino acid possessing branching point is the key for the successful synthesis CQDS.•Lysine-based CQDs are highly nontoxic and biocompatible, enabling bioimaging of cellular media with high degree of physiological safety. Water-soluble carbon quantum dots presenting strong blue photoluminescence with the quantum yield up to 23.3% are simply prepared by microwave treatment of lysine as a building block within 5min in household microwave oven. The formation of lysine-based carbon quantum dots is estimated to proceed through the microwave induced thermal polyamidation and the subsequent carbonization reaction. More importantly, the control experiments using the other amino acids having linear structures reveals that the branched molecular structure of lysine (AB2 type polyamidation monomer) is one of prerequisite points to obtain strongly luminescent carbon quantum dots with high mass yield. Lysine-based carbon quantum dots are highly nontoxic and biocompatible, enabling bioimaging of cellular media with high degree of pysiological safety.