Controlling silica coating thickness on TiO2 nanoparticles for effective photodynamic therapy.

Photosensitive nanoparticles are useful in developing phototherapeutic agents for targeted cancer therapy. In this paper, core-shell structured titanium dioxide-silica (TiO2-SiO2) nanoparticles, with varying shell thickness, were synthesized. The influence of the silica shell thickness on the photoreactivity, cytotoxicity and photo-killing ability of the TiO2 nanoparticles was investigated. Silica coating reduced the photocatalytic reactivity but improved the cytocompatibility of the TiO2 nanoparticles. This effect was amplified with increasing silica shell thickness. When the silica thickness was about 5.5 nm, the coated TiO2 not only retained a high level photodynamic reactivity, comparable to the non-coated TiO2 nanoparticles, but also demonstrated an improved cell compatibility and effective photo-killing ability upon the mouse fibroblast cells (L929).