Laser-Synthesized Carbon-Coated Elemental Bismuth Nanoparticles for Sustained Reactive Oxygen Species Generation Under Visible-Light Irradiation.

Owing to its visible light-responsive electronic properties, redox activity, and potential biocompatibility, elemental bismuth is a promising candidate for photodynamic and chemodynamic therapies primarily via reactive oxygen species generation. However, accelerated surface oxidation of zero-valent bismuth suppresses photoinduced charge transfer, limiting its practical application. Here we introduce metallic bismuth core-shell nanoparticles produced by femtosecond laser ablation in acetone, featuring a crystalline Bi° core encapsulated within a conformal amorphous carbon shell (∼5 nm thick), proved via TEM. XPS with depth profiling confirms that metallic bismuth dominates the nanoparticles' composition, with oxygen-containing species confined to a thin, buried interfacial region. Optical absorption measurements show a broadband response across the visible range, with no oxide-associated features. Under visible irradiation, these nanoparticles exhibit sustained photoinduced redox activity, leading to the formation of hydroxyl radicals, quantified using a coumarin fluorescence assay. Methylene blue degradation is used as a model reaction to investigate charge transfer pathways and wavelength dependence, supporting a dye-sensitization-assisted mechanism mediated by the Bi0 surface. Repeated irradiation cycles preserve photoactivity, consistent with resistance to chemical deactivation under the tested conditions. The demonstrated design provides a basis for controlled redox activity relevant to photo-assisted therapeutic approaches and related biomedical technologies.