Enhanced Stability and Prolonged Insect-Repellent Action of Essential Oil-Loaded Nanostructured Lipid Carriers

Mosquito-borne diseases are a global health concern, necessitating effective and long-lasting insect repellents. This study investigated the physicochemical properties, stability, release kinetics, and efficacy of nanostructured lipid carriers (NLCs) and conventional emulsions (CEs) containing essential oils (NLC EOs) for insect-repellent applications. The droplet size of the CE was 18.46 ± 1.78 μm (Span 0.27 ± 0.06), while the NLC measured 136 ± 10.7 nm (PDI 0.26 ± 0.2) with a ζ-potential of –68 mV ± 2.2 mV (width 4.3 ± 0.1). EO incorporation did not significantly alter droplet size or ζ-potential. Gas chromatography–mass spectrometry confirmed an EO content of 8.57 ± 0.15 mg/mL in the CE EO and 7.75 ± 0.05 mg/mL in the NLC EO, with the NLC retaining a higher EO content over 90 days. Stability tests demonstrated consistent droplet sizes and ζ-potential for both formulations during storage. Release kinetics revealed diffusion-based release mechanisms, with the NLC providing a more sustained release than the CE. In a field test against mosquito species most frequently found in Greece, the NLC EO exhibited a significantly longer complete protection time (CPT) of 45 min, demonstrating more effective, long-lasting insect-repellent action. These findings revealed the NLC’s ability to retain volatile EO components efficiently, offering promising implications for long-lasting insect-repellent action.