NIRvana in Bioimaging: Crafting Biocompatible Graphene Quantum Dots from Everyday Precursors*

Graphene quantum dots (GQDs) have gained attention in the bioimaging community due to their biocompatibility and enhanced imaging depth in the near-infrared (NIR). Developing and optimizing a facile synthesis method of biocompatible NIR fluorescent GQDs from a variety of precursors remains, therefore, a critical task. Herein, we synthesized various GQD structures capable of fluorescing in the NIR via facile bottom-up pyrolysis of precursor materials (ascorbic acid, chitosan, citric acid-urea, dextran, glucose, glucosamine hydrochloride, hyaluronic acid, l-glutamic acid, polyethyleneimine (PEI), polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), sodium cholate, or sodium citrate). In addition to exhibiting NIR fluorescence, all GQDs also showed remarkable biocompatibility at a concentration of 1 mg/mL, as evaluated by the MTT assay, making them suitable for various biological and therapeutic applications. This work provides a unique comprehensive study exploring a scalable and cost-effective process to synthesize NIR-emissive highly biocompatible GQDs from 13 precursors while theoretically describing their optical properties. Due to their exceptional biocompatibility and NIR emission, GQD structures developed here are expected to become prominent candidates for future clinical fluorescence imaging applications.