Photoexcited zinc oxide nanoparticles induce acute toxicity in Aedes aegypti larvae

This study investigates the photoexcited larvicidal toxicity of zinc oxide (ZnO) nanoparticles against Aedes aegypti larvae under ultraviolet A (UV-A) irradiation. Three ZnO samples with different particle sizes were prepared from a colloidal suspension, with the smallest fraction (ZnO-C1) exhibiting an average hydrodynamic diameter of 70.85 nm, while the largest reached 3250 nm. No larval mortality was observed under dark conditions. In contrast, acute toxicity occurred only upon UV-A exposure, revealing a significant light-dependent toxic response that has been less explored in the context of specific ZnO size fractions. Larvicidal bioassays conducted according to World Health Organization guidelines demonstrated a remarkably low LC₅₀ value of 2.50 mg/L for ZnO-C1, among the lowest reported for ZnO-based larvicidal activity. FESEM-EDX analysis detected zinc within the larval body and midgut, indicating nanoparticle uptake through ingestion and respiration. Mechanistic evaluation suggests that UV photoexcitation generates electron-hole pairs in ZnO, promoting the formation of reactive oxygen species (ROS) and Zn²⁺ ions that cause membrane disruption and internal tissue damage. The enhanced toxicity of ZnO-C1 is attributed to its smaller size, larger surface area, and improved dispersion stability, which facilitate greater ROS generation and ionic dissolution. These findings demonstrate a distinct UV-dependent mode of action and highlight the potential of nanoscale ZnO as a photoactivated larvicidal agent against Ae. aegypti.