Red-emissive nitrogen-doped carbon dots from sisal waste: Facile fabrication and a potent dual-type (I/II) ROS photosensitizer for efficient photodynamic tumor ablation.

The valorization of agricultural waste and the development of efficient photosensitizers for photodynamic therapy (PDT) remain two pressing challenges. Herein, we report a facile one-pot hydrothermal strategy to convert sisal processing waste into red-emissive nitrogen-doped carbon dots (N-CDs) using urea as a nitrogen source. The resulting N-CDs exhibit excellent water dispersibility, a uniform size of around 3.26 nm, and a distinct dual-emission feature with a red fluorescence peak at 673 nm. Notably, the N-CDs function as a potent dual-type (I/II) photosensitizer, generating both superoxide anion (O2•-) and singlet oxygen (1O2) upon 660 nm laser irradiation, as confirmed by electron spin resonance spectroscopy and various ROS indicators. In vitro assays demonstrate that N-CDs possess low dark cytotoxicity and induce significant light-triggered cell death. In vivo studies using a4T1 tumor-bearing mouse model reveal that intratumoral injection of N-CDs followed by 660 nm irradiation achieves near-complete tumor ablation, accompanied by activation of systemic antitumor immune responses. This work not only offers a sustainable route for sisal waste valorization but also provides a promising red-emissive carbon-based photosensitizer for effective cancer PDT.