Enriched graphitic N dopants of carbon dots as F cores mediate photothermal conversion in the NIR-II window with high efficiency

We have developed the rapid synthesis of NIR-II-responsive carbon dots (NIR-II-CDs) under microwave irradiation conditions. A close correlation between the photothermal effects and graphitic N doping level is well established by two observed effects: 1) absorbance at 808 and 1064 nm was consistently proportional to the graphitic N content; 2) the photothermal conversion efficiency remarkably increased with the graphitic N content. We further revealed a distinct photothermal conversion mechanism in the NIR-II-CDs, where doped graphitic N sites as paramagnetic F centers can mediate the highly efficient NIR absorption and photothermal conversion. Importantly, readily derived NIR-II-CDs with a graphitic N doping level as high as 4.30 at.% showed ultrahigh photothermal conversion efficiency of 81.3% in the NIR-II window. Using NIR-II-CDs or their hybrid liposomal formula as single PTT or imaging-guided PCT agents, complete tumor ablation without recurrence was realized under the 1064-nm laser irradiation at low laser power densities even in the presence of the breast tissue with a thickness larger than 10 mm. Our results suggest that the photothermal properties of biocompatible CDs can be regulated in the extended NIR regions by doping a high concentration of graphitic N defects as color centers for tumor treatment with minimized side effects. (c) 2020 Elsevier Ltd. All rights reserved.