Nanocarriers can provide controlled and sustained micronutrient delivery to food crops via foliar application, which can potentially reduce energy and water consumption, and soil and groundwater pollution. However, the uptake and translocation of nanocarriers encapsulated micronutrient have not been demonstrated. The objectives of this study were to compare the efficiency of Zn uptake using core-shell ZnO nanoparticles encapsulated in a nano sized mesoporous SiO₂ shell (ZnO@SiO₂NPs) to bare ZnO nanoparticles (ZnO NPs), and Zn salt (ZnCl₂) to tomato plants (Solanum lycopersicum), and to assess the particulate translocation of ZnO@SiO₂ NPs to different plant parts. In this study, ~70 nm ZnO@SiO₂ NPs with ~23 nm ZnO NP core were synthesized for delivery of Zn to plants by foliar uptake. In a model plant media (pH = 5), compared to the rapid dissolution of bare ZnO NPs (90% Zn dissolution after 4 h), ZnO@SiO₂ NPs released Zn at a slower rate (40% Zn dissolution after 3 weeks). The slow and controlled release of ZnO@SiO₂ NPs enabled a sustained Zn delivery over a longer period. A dosing of 40 µg Zn micronutrient of either ZnO@SiO₂ NPs suspension, ZnO NPs suspension or ZnCl₂ solution was performed on a single leaf after 2 weeks of plant growth period for different Zn treatments. The amount of Zn translocated in different treatments were measured by acid digestion of the plant followed by Inductively Coupled Plasma Mass Spectroscopy and Inductively Coupled Plasma Optical Emission Spectroscopy analyses. For ZnO NPs treatment, no Zn uptake was observed after 2 days of dosing. For ZnCl₂ treatment and ZnO@SiO₂ treatment, similar amounts of Zn uptake and translocation to upper leaves, shoots were observed 2 days after dosing (15.5 ± 2.4 µg Zn and 11.4 ± 2.2 µg Zn for ZnCl₂ treatment and ZnO@SiO₂ treatment, respectively). Most ZnO@SiO₂ NPs were translocated in plants in its particulate form as evident from single particle inductively coupled plasma mass spectrometry measurement on different plant parts and transmission electron microscopy analysis on the cross section of the dosed leaf. These results suggest that the SiO₂ shell enhanced the uptake of ZnO NPs in tomato plants. ZnO@SiO₂ NPs had a better delivery efficiency compare to bare ZnO NPs and is likely to be able to provide Zn over a significant period of the plant growth period, reducing the need for multiple applications.

Xiaoyu Gao

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