Coupling BODIPY with nitrogen-doped graphene quantum dots to address the water solubility of photosensitizers

Abstract

The potential of photodynamic therapy (PDT) applications is based primarily on the selection of suitable photosensitizers (PSs). However, highly efficient PSs producing singlet oxygen and other reactive oxygen species (ROS) often have poor water solubility and tend to aggregate in biological media. The most common alternative strategy to address the solubility of PSs is based on difficult-to-control encapsulation or conjugation to liposomes, micelles, or other nanoparticles via surface non-covalent interactions. Covalent functionalization remains relatively unexplored for common PSs. Here, we report a strategy to use highly efficient but poorly water-soluble BODIPY PSs connected to the surface of nitrogen-doped graphene quantum dots (NGQDs) through controlled covalent functionalization. These NGQD–BODIPY PSs do not aggregate in aqueous solutions and generate ROS upon irradiation with visible light, with singlet-oxygen production quantum yields up to 83%. In vitro fluorescence bioimaging was used to confirm that the PSs reside mostly in the cytoplasmic region of human cervical cancer cells (HeLa), and the system reduced the cell viability by ∼85% upon irradiation.