Saccharide-Passivated Graphene Quantum Dots from Graphite for Iron(III) Sensing and Bioimaging

So far, it is difficult to prepare graphene quantum dots (GQDs) with high quantum yield (QY), high biocompatibility, and high yield by conventional top-down methods. We describe here a facile strategy to synthesize GQDs in NaOH/N-methylpyrrolidone (NMP) under sonication, which was subsequently passivated by saccharide to improve their stability. In the synthesis process, the GQDs were predominantly generated through exfoliation of graphite sheets. NaOH boosted the formation of GQDs by intercalation into the layer of graphite sheets, and the yield could be effectively increased to 7.54% with a prolonged sonication time and enhanced power, which was different from traditional methods. Due to the structure of the GQDs being similar to that of pristine graphene, GQDs possessed relatively high QYs, up to 19.12%. With further functionalization by hydrophilic saccharide, xylan-passivated GQDs with better stability and QY were applied for the detection of Fe3+ in the range of 0–75 μM with a limit of detection of 92.8 nM. Furthermore, chitosan-oligosaccharide (COS)-passivated GQDs showed good performance in cell imaging. Therefore, this work provides an efficient method to prepare GQDs and presents their promising application in ferroptosis after passivation.