Carbon Dot-Passivated Black Phosphorus Nanosheet Hybrids for Synergistic Cancer Therapy in the NIR-II Window

Metal-free layered black phosphorus (BP) nanosheets with an excellent photothermal effect and large surface areas have been widely applied in biomedicine but are easily oxidized in ambient conditions yielding insulating phosphorus oxides adsorbed on its surface. Several chemical-functionalized strategies have been explored to protect thin layers of BP; however, the performance of passivated BP often decreases significantly, falling behind the single BP due to the strong structure perturbation. Herein, we designed and constructed 0D/2D hybrid photothermal agents by assembling NIR-II-responsive carbon dots (NIR-II-CDs) on BP nanosheets. NIR-II-CDs improve the ambient stability of BP by isolating them from water and oxygen and enhance the photothermal properties of BP nanosheets. Such NIR-II-CD/BP hybrids strengthen the light-harvesting ability, achieving high photothermal conversion efficiencies in the NIR-I (77.3%) and NIR-II (61.4%) windows, which is significantly higher than that of pristine BP (49.5 and 28.4% at 808 and 1064 nm). Owing to the intrinsic advantage of 1064 nm laser and the excellent PTT effect of our NIR-II-CD/BP hybrids, complete tumor eradication was realized in a deep-tissue tumor model.