Precursor-dependent optical and structural properties of eleven NIR-emissive graphene quantum dots for bioimaging applications.

Graphene quantum dots (GQDs) have emerged as important bioimaging tools because of their biocompatibility and the ability of some to perform deep-penetration near-infrared (NIR) fluorescence imaging. The development of NIR-fluorescent GQDs from various precursors can enhance their use in multiplex imaging, multi-analyte sensing, and combination therapy delivery. Herein, we present the synthesis of an unprecedented set of 11 distinct GQD structures capable of NIR fluorescence, achieved through microwave-assisted bottom-up carbonization of 11 precursors: ascorbic acid, chitosan, citric acid-urea, dextran, glucose, glucosamine hydrochloride, hyaluronic acid, L-glutamic acid, polyethylene glycol, sodium cholate, or sodium citrate. All GQDs exhibit biocompatibility at up to 2.20 mg ml^-1 and can be tracked in vitro by their NIR fluorescence, while demonstrating effective internalization in human embryonic kidney-293 cells. This work provides a unique, comprehensive study, offering versatility in synthesis and physical/chemical properties of biocompatible NIR-emitting GQDs suited for a range of bioimaging applications.