▎ 摘　　要

Humic acid as a raw material was applied for the preparation of graphene quantum dots (GQDs) by a simple one-step hydrothermal method. Transmission electron microscopy (TEM) images show that GQDs are highly crystalline with an average size of 4 nm. Fourier transform infrared (FT-IR) spectra and X-ray photoelectron spectra (XPS) suggest the existence of functional groups such as hydroxyl and carboxylic groups on the surface of GQDs, which makes the synthesized GQDs water-soluble. Optical properties of GQDs were characterized by photoluminescence (PL) spectra and ultraviolet-visible (UV-vis) spectroscopy. It is observed that GQDs exhibit stable, excellent excitation-dependent photoluminescence. Therefore, the as-prepared GQDs can be applied as fluorescent materials for bioimaging. Cellular imaging studies indicate that GQDs can clearly label cells. This study provides a novel low-cost raw material for the synthesis of fluorescent quantum dots by a facile method, which may have wide applications in biomedical fields.