Uptake and Translocation of Mesoporous SiO2-Coated ZnO Nanoparticles to Solanum lycopersicum Following Foliar Application

Nanoparticles composed of ZnO encapsulated in a mesoporous SiO2 shell (nZnO@SiO2) with a primary particle diameter of ∼70 nm were synthesized for delivery of Zn, a micronutrient, by foliar uptake. Compared to the rapid dissolution of bare nZnO (90% Zn dissolution after 4 h) in a model plant media (pH = 5), nZnO@SiO2 released Zn more slowly (40% Zn dissolution after 3 weeks), thus enabling sustained Zn delivery over a longer period. nZnO@SiO2, nZnO, and ZnCl2 were exposed to Solanum lycopersicum by dosing 40 μg of Zn micronutrient (in a 20 μL suspension) on a single leaf. No Zn uptake was observed for the nZnO treatment after 2 days. Comparable amounts of Zn uptake were observed 2 days after ZnCl2 (15.5 ± 2.4 μg Zn) and nZnO@SiO2 (11.4 ± 2.2 μg Zn) dosing. Single particle inductively coupled plasma mass spectrometry revealed that for foliar applied nZnO@SiO2, almost all of the Zn translocated to upper leaves and the stem were in nanoparticulate form. Our results suggest that the SiO2 shell enhances the uptake of ZnO nanoparticles in Solanum lycopersicum. Sustained and controlled micronutrient delivery in plants through foliar application will reduce fertilizer, energy, and water use.