Sunlight-Activatable ROS Generator for Cell Death Using TiO₂/c-Si Microwires

Solar-driven reactive oxygen species (ROS) generation is an attractive disinfection technique for cell death and water purification. However, most photocatalysts require high stability in the water environment and the production of ROS with a sufficient amount and diffusion length to damage pathogens. Here, a ROS generation system was developed consisting of tapered crystalline silicon microwires coated with anatase titanium dioxide for a conformal junction. The system effectively absorbed >95% of sunlight over 300-1100 nm, resulting in effective ROS generation. The system was designed to produce various ROS species, but a logistic regression analysis with cellular survival data revealed that the diffusion length of the ROS is ∼9 μm, implying that the most dominant species causing cell damage is H₂O₂. Surprisingly, a quantitative analysis showed that only 15 min of light irradiation on the system would catalyze a local bactericidal effect comparable to the conventional germicidal level of H₂O₂ (∼3 mM).