Photoactivation of core-shell titania coated upconversion nanoparticles and their effect on cell death

Titania (TiO₂) has been explored as a potential drug in eradicating cancer by virtue of its photocatalytic property to generate reactive oxygen species (ROS) under UV irradiation. Its clinical application, however, has been hampered by the tissue penetration depth limit of the UV light needed for its activation. The use of 'invisible' near-infrared (NIR) light affords greater tissue penetration depth because most tissues are 'transparent' to NIR light. Here, we uniformly coated TiO₂ to a nanometer-sized light transducer that can upconvert highly penetrating NIR light to the activation absorption spectrum of TiO₂ at UV range. Under NIR excitation, photoinduced TiO₂ by the upconverted UV light results in the generation of more than one type of ROS that was stably produced under an appropriate storage condition. The amount of ROS produced was also effective in killing cancer cells in vitro, thus suggesting its potential in overcoming the current penetration depth limit.