Nitrogen and Boron Dual-Doped Graphene Quantum Dots for Near-Infrared Second Window Imaging and Photothermal Therapy.

Fluorescence imaging of biological systems in the second near-infrared window (NIR-II) has recently drawn much attention because of its negligible background noise of autofluorescence and low tissue scattering. Here we present a new NIR-II fluorescent agent, graphene quantum dots dual-doped with both nitrogen and boron (N-B-GQDs). N-B-GQDs have an ultra-small size (~ 5 nm), are highly stable in serum, and demonstrate a peak fluorescent emission at 1000 nm and high photostability. In addition to the NIR-II imaging capability, N-B-GQDs efficiently absorb and convert NIR light into heat when irradiated by an external NIR source, demonstrating a photothermal therapeutic effect that kills cancer cells in vitro and completely suppresses tumor growth in a glioma xenograft mouse model. N-B-GQDs demonstrate a safe profile, prolonged blood half-life, and rapid excretion in mice, which are the characteristics favorable for in vivo biomedical applications.