Carbon Dots as Multifunctional Phototheranostic Agents for Photoacoustic/Fluorescence Imaging and Photothermal/Photodynamic Synergistic Cancer Therapy

Phototheranostics combines diagnosis and image-guided therapy of disease using a single agent, which makes it a potential clinical approach for cancer treatment. However, as the core element of phototheranostics, most phototheranostic agents are activated by the UV-visible light, which falls outside of the phototherapy window and results in poor tissue penetration capability. Moreover, they are in general only capable of generating reactive oxygen species or heat. To integrate photodynamic and photothermal therapies into a single treatment modality is thus expected to broaden the applicability and improve the efficiency of this technique. In this work, carbon dots (CDs) with absorption range up to 1100 nm are synthesized by hydrothermal treatment of 1,3,6-trinitropyrene and Na2SO3. The CDs could simultaneously present strong fluorescence and generate 1O2 through two-photon excitation mechanism, and they also show outstanding photothermal conversion capability under irradiation by an 800 nm femtosecond pulsed laser. Moreover, the broad absorption spectrum of the CDs enable them to be used as an agent for photoacoustic (PA) imaging. The in vitro and in vivo experiments demonstrate that the CDs have good biocompatibility and can serve as multifunctional phototheranostic agents for PA/fluorescence imaging, and photodynamic/photothermal synergistic cancer therapy using a single near-infrared laser.