Controlled aggregation of methylene blue in silica-methylene blue nanocomposite for enhanced 1O2 generation

Organic photosensitizers can facilitate photochemical singlet-oxygen (O-1(2)) production, providing a promising strategy for photocatalysis, photodynamic therapy, and environmental protection. Unfortunately, most organic photosensitizers tend to self-aggregate because of their hydrophobicity and conjugated pi-pi electronic structure, leading to the inactivation of their photosensitizing capabilities. Thus, the controlled aggregation of organic photosensitizers is critical for photosensitizer's applications. We report a nanocomposite of porous silica nanoaggregates and the organic photosensitizer methylene blue (P-SiOx NAs/MB) that allows the aggregation control of methylene blue (MB). This nanocomposite-photosensitizer consists of highly dispersed MB in P-SiOx NAs and enhances O-1(2) production under light irradiation without the inactivation of the photosensitizing ability of MB. The enhanced O-1(2) generation rate of P-SiOx NAs/MB is 1.36 times larger than that of free MB. This behavior is contrasted with the inactivation of the photosensitizing ability of MB-encapsulated organo-silica nanoparticles, due to MB self-aggregation within the particles. This study provides a strategy for creating an efficient photosensitizer via suppression of MB self-aggregation to enhance the generation of O-1(2).