Photoactive Red Fluorescent SiO(2 )Nanoparticles Based on Controlled Methylene Blue Aggregation in Reverse Microemulsions br

We present a reverse microemulsion synthesis procedure forincorporating methylene blue (MB), a known FDA-approved type-II red-absorbingphotosensitizer and1O2generator, into the matrix of hydrophobic-core/hydrophilic-shell SiO2nanoparticles. Different synthesis conditions were explored with the aim ofcontrolling the entrapped-dye aggregation at high dye loadings in the hydrophobicprotective core; minimizing dye aggregation ensured highly efficient photoactivenanoentities for1O2production. Monitoring the synthesis in real time using UV-visabsorption allowed tracking of the dye aggregation process. In particular, silicananoparticles (MB@SiO2NPs) of similar to 50 nm diameter size with a high local entrapped-MB concentration (similar to 10-2M, 1000 MB molecules per NP) and a moderate proportionof dye aggregation were obtained. The as-prepared MB@SiO2NPs showed a highsinglet oxygen photogeneration efficiency (Phi Delta= 0.30 +/- 0.05), and they can be alsoconsidered as redfluorescent probes (Phi F similar to 0.02,lambda max similar to 650 nm). The distinctivephotophysical and photochemical characteristics of the synthesized NPs reveal that the reverse microemulsion synthesis procedureoffers an interesting strategy for the development of complex theranostic nano-objects for photodynamic therapy.