Fabrication of pH-responsive non-phospholipid liposomal nanocarriers for insecticidal activity of thiamethoxam

Non-phospholipid liposomes (sterosomes) composed of cholesterol and stearylamine were fabricated as a sustained and pH-responsive pesticide carrier for controlling the release of thiamethoxam (Thx) agianst Lepidoptera pests. This strategy achieved high insecticidal activity, reduced environmental risks and improved targeting of pesticides. Thx-loaded sterosomes were prepared by repeated freeze-thaw cycles and characterized with field emission scanning electron microscopy (FE-SEM). The size distribution and ζ-potential were also determined. The results demonstrated that sterosomes (173.7 nm ± 1.6 nm) exhibited good dispersibility and stability. The drug loading was 8.97%. Prolonged drug release was obtained at pH 7.0, which would help to achieve drug delivery with the movement of the carriers and effectively reduce the release rate of Thx, while at pH 10.0, the release rate was accelerated, due to the phase separation between deprotonated stearylamine and cholesterol. This property may improve the accumulation of Thx in the gut of Lepidoptera, as their digestive tract has a unique highly alkaline pH. The insecticidal effect was evaluated using Ostrinia furnacalis as the model insect, and the survival rate of Thx-sterosomes group (effective Thx 6 mg/mL) was lower than 60% after 1 day. Thx-loaded sterosomes showed better efficacy and a stronger insecticidal activity than the free Thx solution. Thx-loaded sterosomes exhibited sustained and pH-responsive controlled release of the pesticide, suggesting a practically and economically desirable strategy for the preparation of novel pesticide formulations.