Ultrastable Amine, Sulfo Cofunctionalized Graphene Quantum Dots with High Two-Photon Fluorescence for Cellular Imaging

Fluorescent probes with superior two-photon fluorescence are highly attractive in the field of bioimaging. Herein, we report a one-pot hydrothermal route to synthesis amine, sulfo cofunctionalized graphene quantum dots (GQDs), which acts as efficient one-photon and two-photon fluorescent probes for cellular imaging. As synthesized GQDs exhibit ultrastability due to the edge-site functionalization of amine and sulfo groups. In addition, GQDs display attractive two-photon fluorescence properties. The two-photon absorption cross section of GQDs reaches up to 31,000 GM, which substantially exceeds that of the majority of traditional fluorescent materials. Furthermore, the noncytotoxicity GQDs exhibit a negligible photothermal effect under 808 nm femtosecond laser irradiation, which is suitable for long-term two-photon imaging and observation. These findings open new possibilities for using two-photon fluorescent GQDs in various biological applications.