1. Introduction
The development of graphene quantum dots with distinct properties and wide-ranging applications in electrochemical luminescence, bioimaging, photocatalysis, and ion detection is attracting increased attention [1–5]. From the visible to the nearinfrared region, diverse sizes of graphene quantum dots with different photoluminescence colors have been adopted by various synthetic "top–down" and "bottom–up" methods. The grapheme quantum dots show satisfactorily low toxicity, good biocompatibility, stable photoluminescence, excellent solubility, and better surface grafting, which make them promising in optoelectronic devices, bioimaging, and sensors