The present invention relates to a photosensitizer-containing nanoparticle, comprising a photosensitizer covalently bonded throughout at least a part of said nanoparticle to the nanoparticle matrix material and incorporated therein in a quasi-aggregated state. The present invention further relates to methods for producing the invention nanoparticles, and to methods of killing cancer cells by PDT treatment using the said nanoparticles.
