Comparative Investigation of Graphene Quantum Dots and Graphitic-phase C3N4 Nanosheets in Terms of Photoluminescence Properties and Biomedical Imaging

Abstract

In this work, highly water-dispersible graphene quantum dots (GQDs) and graphitic-phase C3N4 (g-C3N4) nanosheets were prepared by a similar top-down process, chemically oxidizing thermally exfoliated graphite oxide and bulk g-C3N4 with concentrated nitric acid, respectively. UV-Vis absorption and photoluminescence (PL) spectral analyses were used to compare their optical properties. Compared to GQDs, g-C3N4 nanosheets demonstrate higher PL quantum yield. Cytotoxicity measurements indicate that both GQDs and g-C3N4 nanosheets are of low cytotoxicity with favorable biocompatibility. The remarkable performances of GQDs and g-C3N4 nanosheets in biomedical imaging are demonstrated by a simple incubation study with HepG2 cells. The HepG2 cells incubated with these two materials for 12 h do not weaken the cell activity and maintain their normal morphology. GQDs can effectively distribute in not only the cell membrane and cytoplasm, but also the nucleus, while the g-C3N4 nanosheets mainly exist at the cell’s membrane and cytoplasm. All these studies suggest that both as-prepared GQDs and g-C3N4 nanosheets are greatly promising for biomedical imaging application.