This work focused on the delivery of dsRNA either complexed with poly-L-arginine (PLR-polyplex) or loaded onto poly-L-arginine functionalized 20 nm Au nanoparticles (PLR/Au NPs). RNA interference (RNAi) of a luciferase gene expressed in Spodopteria f rugiperda Sf9 stable cell line (Sf 9_LUC) was used as a model system. The binding affinity of dsRNA with two modes of functionalization of Au NPs was investigated: the electrostatic binding of PLR on citrate stabilized Au NPs (e-PLR/Au NPs) via the layer-by-layer method or the covalent-linking reaction of the polymer with NHS groups on the Au NPs surface (c-PLR/Au NPs) with excess groups quenched with either hydroxylamine (c-PLR/Au/Hyd NPs) or bovine serum albumin (c-PLR/Au/BSA NPs). The formation of PLR-polyplex particles resulting from the complexation of PLR and dsRNA were revealed by transmission electron microscope (TEM), scanning transmission electron microscope (STEM), and elemental mapping by energy dispersive X-ray spectroscopy (EDS). Luciferase gene knockdown was evaluated after exposure of Sf9 cells for 72 h to 600 ng of dsRNA. Gene knockdown (GK) was found to be more efficient by exposing Sf9 cells to nanoscaled (size <100 nm) PLR-polyplex (58% GK), in contrast to microscaled (size >1 μm) PLR-polyplex (20% GK) or covalent PLR/Au/Hyd (7% GK) particles. The replacement of hydroxylamine by bovine serum albumin as ligand has significantly enhanced the efficiency of GK (31% GK). Investigation of endosomal escape, a key physiological barrier for dsRNA delivery, with CypHer5E labeled dsRNA showed the good ability for the dsRNA conjugated to the different nanosystems to enter the cells compared to the unconjugated one. This study provides valuable information concerning the required properties of materials used for dsRNA delivery in lepidopteran cells such as nanoparticle size, stability in the cell culture media, the polymer molecular weight and binding strength to the nanoparticle, and the nature of ligands on the surface.

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This study investigated the potential of ZnO-nanoparticle (NP) seed treatments for enhancing Zn nutrition in wheat (Triticum aestivum). We tested bare, ZnO core Zn 3 (PO 4 ) 2 shell, dextran (DEX)-coated, and dextran sulfate (DEX(SO 4 ))-coated ZnO NPs and ZnSO 4 solution as an ionic control. We measured root and shoot Zn concentrations, lengths, biomasses, and seed germination upon termination of the assay. All ZnO NPs were more effective than ZnSO 4 in increasing tissue Zn concentrations and seedling growth. Exposure to higher concentrations of ZnSO 4 significantly decreased growth and germination rates relative to those of the controls and the ZnO-NP groups, whereas none of the ZnO NPs significantly affected seed germination. Bare and DEX−ZnO NPs increased Zn concentrations in wheat without decreasing growth. The results of this study demonstrated that ZnO NPs can be used as an effective seed treatment to enhance both Zn nutrition and plant growth.

Conventional synthetic insecticides have limited success due to insect resistance and negative effects on off-target biota and the environment. Although RNA interference (RNAi) is a tool that is becoming more widely utilized in pest control products, naked dsRNA has limited success in most taxa. Nanocarriers have shown promising results in enhancing the efficacy of this tool. In this study, we used a layer-by-layer electrostatic assembly where we synthesized poly(acrylic acid) (PAA)-coated hydroxyapatite (HA) nanoparticles (PAA-HA NPs) as inorganic nanocarriers, which were then coated with a layer of a cationic poly(amino acid), 10 kDa poly-L-arginine (PLR 10 ), to allow for binding of a layer of negatively charged dsRNA. Binding of PLR 10 -PAA-HA NPs to dsRNA was found to increase as the mass ratio of NPs to dsRNA increased. In vitro studies with transgenic SF9 cells (from Spodoptera frugiperda) expressing the firefly luciferase gene showed a significant gene silencing (35% decrease) at a 5:1 NP-to-dsRNA ratio, while naked dsRNA was ineffective at gene silencing. There was a significant concentration−response relationship in knockdown; however, cytotoxicity was observed at higher concentrations. Confocal microscopy studies showed that dsRNA from PLR 10 -PAA-HA NPs was not localized within endosomes, while naked dsRNA appeared to be entrapped within the endosomes. Overall, polymer-functionalized HA nanocarriers enabled dsRNA to elicit gene knockdown in cells, whereas naked dsRNA was not effective in causing gene knockdown.

Soil pH and dissolved organic matter (DOM) content are among the most important factors affecting the bioavailability of Zn and the binding and dissolution of ZnO nanoparticles (NPs).