Insecticide@Silica Nanocontainers with High Cypermethrin Load and Improved Photostability

Cypermethrin (CM) is a widely used insecticide to repel and control stinging, biting and sucking-licking insects. To limit the required CM amount, to reduce application cycles, and to increase its stability, we developed CM@OS core@shell nanocontainers (OS: n-octylsilicate) as a novel synthesis concept and material. The CM@OS core@shell nanocontainers are synthesized via a solvent/antisolvent approach. They exhibit a mean total diameter of 34 ± 8 nm with a CM particle core of 15 ± 3 nm in diameter and an OS particle shell of 7 ± 2 nm in thickness. Due to negative surface charging (–63 ± 1 mV), the as-prepared nanocontainers are colloidally very stable as aqueous suspensions. Analytical characterization is performed by electron microscopy (SEM, TEM, STEM), electron spectroscopy (EDXS), and additional methods (DLS, zeta-potential analysis, FT-IR, TG, C/H/N/S analysis, photometry). The CM content is 10 wt-%, and CM is photochemically significantly stabilized in regard of a cleavage of the ester group as well as of the cyclopropanyl ring in comparison to free CM. Thin-films are realized, and the slow CM release exemplary shown, and promoted by the lipophilic functionality of OS.