A stable nanoliposomal carboxymethyl cellulose hydrogel of Pelargonium essential oil: Formulation, characterization, and enhanced repellent activity against Anopheles stephensi

The development of effective botanical repellents is a key strategy in reducing reliance on synthetic compounds such as N,N-Diethyl-meta-toluamide (DEET). This study reports the design and evaluation of a topical nanoliposomal hydrogel incorporating Pelargonium graveolens essential oil (PEO) for repellency against Anopheles stephensi . Nanoliposomes were prepared using ethanol injection, loaded with 3% PEO, and incorporated into a carboxymethyl cellulose (CMC) hydrogel. The formulation was characterized by dynamic light scattering (DLS), zeta potential, Fourier Transform Infrared (FTIR) spectroscopy, and viscosity analysis. Repellent efficacy was assessed using the arm-in-cage method against unfed female An. stephensi , with complete protection time (CPT) recorded for the nanoliposomal gel (LipoGel 3%), compared to free PEO (3%), DEET (3%), and a blank gel. PEO was characterized by Gas Chromatography-Mass Spectrometry (GC–MS), with β-citronellol (30.35%) and geraniol (15.54%) as major constituents. LipoGel 3% displayed a mean particle size of 101 ± 0 nm, a narrow size distribution (Span = 0.95), and a zeta potential of −58.63 ± 0.83 mV. The gel exhibited shear-thinning behavior and remained physically stable for six months. In repellent assays, LipoGel 3% provided a CPT of 216 ± 25 min, significantly longer than free PEO (148 ± 23 min) and the blank gel (33 ± 0 min), though shorter than DEET 3% (311 ± 37 min). Encapsulation of Pelargonium essential oil in a nanoliposomal hydrogel significantly prolongs repellent activity against An. stephensi . The formulation presents a stable, natural-based topical repellent worthy of further field assessment. • Nanoliposomal hydrogel delivers Pelargonium oil, providing >3.5 h complete protection against Anopheles stephensi . • Geranium oil major components are β-citronellol (30.35%) and geraniol (15.54%), key for repellent activity. • Formulation shows excellent six-month stability at 4 °C and 26 °C with desirable shear-thinning rheology. • Encapsulation boosts repellent duration by 46% compared to free essential oil, bridging the gap with DEET. • Simple ethanol-injection method yields stable, nanoscale vesicles (~101 nm) with high negative zeta potential.