Incorporation of methylene blue into mesoporous silica nanoparticles for singlet oxygen generation

Abstract

Methylene blue is a known photosensitizer with an ability to generate singlet oxygen. The main active species is the monomeric form. However, this dye has a tendency to self-aggregate to form dimers and higher aggregates, which are less active for ¹O₂ generation. In this study we propose different strategies to incorporate methylene blue into porous silica nanoparticles. The design of the synthesis is a key parameter to avoid both leaching of the dye and its self-aggregation. The negatively charged silica matrix allows the incorporation of the dye, which is cationic, with no leaching, whereas the presence of phenyl functions in the matrix favors the monomeric form of methylene blue (MB). We observe that both dimeric and monomeric forms of MB can generate ¹O₂ species when confined inside a silica matrix, improving the activity compared to the bare dye in solution.