Optimization of Process Parameters to Formulate Nanoemulsion by Spontaneous Emulsification: Evaluation of Larvicidal Activity Against Culex quinquefasciatus Larva

Abstract

Nanoemulsions are colloidal dispersions of oil and water with droplet size in the range of 10–100 nm. They are optically transparent stable systems which require less surfactant concentration than microemulsion. Basil oil (extracted from Ocimum basilicum) nanoemulsion was formulated by spontaneous emulsification method and was stabilized by non-ionic surfactant Tween20. Process parameters like surfactant concentration, stirring speed, and holding temperature were optimized to obtain nanoemulsion with minimized droplet size and these factors demonstrated positive correlation on nanoemulsion droplet size and stability. BT20/11/800/75 nanoemulsion (oil system = basil, surfactant = Tween20, oil to surfactant mixing ratio 1:1 vol/vol, rpm = 800, pre-heating temperature of organic phase = 75 °C) showed lowest droplet size of 28 nm and greater stability. Transmission electron micrograph image showed the spherical morphology of BT20/11/800/75 nanoemulsion droplets. Formulated BT20/11/800/75 nanoemulsion was evaluated for larvicidal activity against Culex quinquefasciatus. Basil oil nanoemulsion exhibited dose-dependent mortality of C. quinquefasciatus larva which increased with increase in exposure time. Lethal concentration (LC50) value decreased from 70 to 3 mg/L−1 with increase in exposure time from 1 to 5 h. Further increase in exposure time did not show any significance reduction in LC-50 value. Histopathological staining revealed the structural and functional changes in nanoemulsion-treated larva. Epithelial cells are swollen and showed distorted morphology. Disintegration of epithelial membrane and peritrophic membrane upon nanoemulsion treatment resulted in leakage of mid-gut lumen contents.