Renal‐Clearable Nickel‐Doped Carbon Dots with Boosted Photothermal Conversion Efficiency for Multimodal Imaging‐Guided Cancer Therapy in the Second Near‐Infrared Biowindow

Abstract Photothermal agents with absorption in the second near‐infrared (NIR‐II) biowindow have attracted increasing attention for photothermal therapy (PTT) on account of their deeper tissue penetration capacity. However, most of the current NIR‐II photothermal agents exhibit low photothermal conversion efficiency (PCE) and long‐term biotoxicity. To overcome these shortcomings, herein, nickel and nitrogen co‐doped carbon dots (Ni‐CDs, ≈4.6 nm) are prepared via a facile one‐pot hydrothermal approach for imaging‐guided PTT in the NIR‐II window. The Ni‐CDs exhibit significant absorption in the NIR‐II region with a distinguished PCE as high as 76.1% (1064 nm) and have excellent photostability and biocompatibility. Furthermore, the Ni‐CDs can be employed as photothermal, photoacoustic, and magnetic resonance imaging contrast agents because of their outstanding photothermal effect and instinctive paramagnetic feature. The Ni‐CDs demonstrate significant PTT efficacy of tumor upon 1064 nm irradiation with a low power density (0.5 W cm −2 ). The Ni‐CDs can be eliminated from the body via a renal filtration pathway, thereby minimizing their long‐term biotoxicity. Therefore, this work provides a simple and feasible approach to develop photothermal agents with remarkable PCE in the NIR‐II region, presenting good biosafety for multimodal imaging‐guided PTT of tumor.