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.

SiO2 is bioinert and highly functionalizable, thus making it a very attractive material for nanotechnology applications such as drug delivery and nanoencapsulation of pesticides. Herein, we synthesized porous hollow SiO2 nanoparticles (PHSNs) by using cetyltrimethylammonium bromide (CTAB) and Pluronic P123 as the structure-directing agents. The porosity and hollowness of the SiO2 structure allow for the protective and high-density loading of molecules of interest inside the nanoshell. We demonstrate here that loading can be achieved post-synthesis through the pores of the PHSNs. The PHSNs are monodisperse with a mean diameter of 258 nm and a specific surface area of 287 m2 g–1. The mechanism of formation of the PHSNs was investigated using 1-D and 2-D solid-state nuclear magnetic resonance (SS-NMR) and Fourier-transform infrared spectroscopy (FTIR). The data suggest that CTAB and Pluronic P123 interact, forming a hydrophobic spherical hollow cage that serves as a template for the porous hollow structure. After synthesis, the surfactants were removed by calcination at 550 °C and the PHSNs were added to an Fe3+ solution followed by addition of the reductant NaBH4 to the suspension, which led to the formation of Fe(0) NPs both on the PHSNs and inside the hollow shell, as confirmed by transmission electron microscopy imaging. The imaging of the formation of Fe(0) NPs inside the hollow shell provides direct evidence of transport of solute molecules across the shell and their reactions within the PHSNs, making it a versatile nanocarrier and nanoreactor.

Pesticide nanoencapsulation and its foliar application are promising approaches for improving the efficiency of current pesticide application practices, whose losses can reach 99%. Here, we investigated the uptake and translocation of azoxystrobin, a systemic pesticide, encapsulated within porous hollow silica nanoparticles (PHSNs) of a mean diameter of 253 ± 73 nm, following foliar application on tomato plants. The PHSNs had 67% loading efficiency for azoxystrobin and enabled its controlled release over several days. Thus, the nanoencapsulated pesticide was taken up and distributed more slowly than the nonencapsulated pesticide. A total of 8.7 ± 1.3 μg of the azoxystrobin was quantified in different plant parts, 4 days after 20 μg of nanoencapsulated pesticide application on a single leaf of each plant. In parallel, the uptake and translocation of the PHSNs (as total Si and particulate SiO2) in the plant were characterized. The total Si translocated after 4 days was 15.5 ± 1.6 μg, and the uptake rate and translocation patterns for PHSNs were different from their pesticide load. Notably, PHSNs were translocated throughout the plant, although they were much larger than known size-exclusion limits (reportedly below 50 nm) in plant tissues, which points to knowledge gaps in the translocation mechanisms of nanoparticles in plants. The translocation patterns of azoxystrobin vary significantly following foliar uptake of the nanosilica-encapsulated and nonencapsulated pesticide formulations.

Porous silica nanocarriers have the potential to improve agricultural crop productivity. However, the impacts of nanoencapsulated pesticides on soil health and plant growth, and how they compare with conventional pesticide...

Polymeric and SiO2 nanoparticles can be used as nanocarriers to improve the efficacy of pesticide delivery in agriculture. However, the environmental fate and potential risks of this type of nanopesticides...