Intracellular Singlet Oxygen Generation Mediated by Upconversion Nanoparticles in RAW 264.7 Macrophages

Upconversion nanoparticles (UCNPs) capable of generating reactive oxygen species under near-infrared (NIR) excitation have emerged as promising platforms for biomedical applications, particularly photodynamic therapy and immune-related modulation. Here, we investigate the biological application of core-shell UCNPs functionalized with a photosensitizer for the intracellular generation of singlet oxygen (¹O₂). The nanoparticles exhibited reproducible morphology, phase purity, and strong upconversion emission intensity, enabling efficient activation under NIR excitation. Murine RAW 264.7 macrophages were employed as a model of innate immune cells to evaluate nanoparticle uptake, cytocompatibility, and light-triggered ¹O₂ production. Luminescence-based assays and microscopy analyses confirmed efficient cellular internalization and localized ¹O₂ generation upon low-energy NIR excitation, while cytotoxicity studies demonstrated low basal toxicity in the absence of irradiation. Upon photoactivation, a significant reduction in cell viability was observed, consistent with photodynamically induced oxidative stress. These results further demonstrate that UCNP-based nanoplatforms can function as effective intracellular generators of reactive oxygen species in phagocytic immune cells and highlight their potential for photodynamic therapy (PDT), redox modulation, and to study molecular interactions at the cell membrane level.