• cell imaging;
  • graphene;
  • pyrroles;
  • quantum dots;
  • UV/Vis spectroscopy


We report the first pyrrole-ring surface-functionalized graphene quantum dots (p-GQDs) prepared by a two-step hydrothermal approach under microwave irradiation in an ammonia medium. The most distinct feature of the functionalized GQDs is that both the excitation and emission wavelengths fall into the visible-light region. The p-GQDs are excited by visible light at λex 490 nm (2.53 eV) to emit excitation-independent photoluminescence at a maximum wavelength of λem 550 nm. This is thus far the longest emission wavelength reported for GQDs. Stable photoluminescence is achieved at pH 4–10 with an ionic strength of 1.2 mol L−1 KCl. These features make the p-GQDs excellent probes for bio-imaging and bio-labeling, which is demonstrated by imaging live HeLa cells.