Amplification of luminescence intensity by ytterbium( <scp>iii</scp> ) dopant in upconversion nanoparticles integrated with carbon dots for NIR-responsive targeted photodynamic therapy

Photodynamic therapy (PDT) is one of the promising fields for cancer treatment, demonstrating precise and significant therapeutic outcomes. Despite their widespread use, conventional photosensitizers show significant limitations and suboptimal integration with other systems for PDT application. Furthermore, most of them require multistep synthesis procedures. To resolve these limitations, it is essential to develop simple methods to prepare more efficient materials for photodynamic therapy. In this work, we report the synthesis of a carbon dot-conjugated upconversion system (UCNP@CDs) <i>via</i> an <i>in situ</i> co-carbonization method, which gets activated under a dual-mode laser (980 nm and 660 nm) for enhanced photodynamic therapy. The whole system works based on the Förster resonance energy transfer (FRET) mechanism, where UCNPs are activated by a 980 nm laser and this energy is transferred to the carbon dots, which in turn behave as a photosensitizer to produce ¹O₂ with 72% cell mortality at a concentration of 100 μg mL^-1. Besides their photosensitizing property, the synthesized carbon dots are derived from folic acid and <i>p</i>- phenylenediamine to achieve active targetability towards cancer cells and exhibit high biocompatibility and water dispersibility. Notably, an <i>in vitro</i> study confirmed that the synthesized nanohybrid targeted the cytoplasm of cancer cells and exhibited considerably pronounced cytotoxicity in the presence of laser irradiation. Therefore, the results of this work demonstrate that the designed nanohybrid has great potential in cancer treatment.