NIR-driven graphitic-phase carbon nitride nanosheets for efficient bioimaging and photodynamic therapy

Photodynamic therapy (PDT) is a noninvasive and promising anticancer therapy modality that utilizes the photochemical reactions of photosensitizers, upon irradiation at a specific wavelength, to yield reactive oxygen species (ROS) to impair malignant cancer cells. As a potential and new two-dimensional layered photosensitizer, graphitic-phase carbon nitride (g-C3N4) exhibits a high blue photoluminescence quantum yield and good biocompatibility, but is challenged by limited narrow absorption in the near-infrared (NIR) region. Herein, in order to broaden its light utilization, unique and original NIR light excited nanocomposites (g-C3N4/UCNP NCs) for PDT based on g-C3N4 nanosheets combined with up-conversion nanoparticles (UCNPs) have been designed. UCNPs can efficiently convert NIR light to ultraviolet and visible tight emissions that match well with the absorption of g-C3N4 nanosheets. The nanocomposites swallowed up by cancer cells are able to yield ROS and suppress tumor cell growth and then induce apoptosis upon NIR laser excitation. This demonstrates the potential of g-C3N4/UCNP NCs as a low-toxic and biocompatible photosensitizer for PDT and for down/up-conversion luminescence imaging.