Exceptionally High Payload of the IR780 Iodide on Folic Acid-Functionalized Graphene Quantum Dots for Targeted Photothermal Therapy

The IR780 iodide (IR780) is recognized as an effective theranostic agent for simultaneous near-infrared fluorescence imaging and photothermal therapy (PTT). However, the rigid chloro-cyclohexenyl ring makes IR780 insoluble in almost all pharmaceutically acceptable solvents, which inevitably limits its clinical application. We report folic acid (FA)-functionalized graphene quantum dots (GQDs-FA) containing a large and intact sp² domain with carboxyl groups around the edge. Such GQDs-FA possess exceptionally high loading capacity for IR780 via strong π-π stacking interactions, and the water solubility of IR780 is improved by over 2400-fold after loading onto GQDs-FA (IR780/GQDs-FA). IR780/GQDs-FA with an improved photostability, an enhanced tumor-targeting ability, and a high photothermal conversion efficiency of 87.9% were capable of producing sufficient hyperthermia to effectively kill cancer cells and completely eradicate tumors upon 808 nm laser irradiation. The present IR780/GQDs-FA may open up great opportunities for the effective PTT to treat cancer.