Nanoemulsion of Lemon Grass ( <i>Cymbopogon flexuosus</i> ) Essential Oil: Stability, Molecular Dynamics, Anticancer, and Antibacterial Potential

Lemon grass essential oil (LEO) derived from lemon grass (Cymbopogon flexuosus) exhibits promising therapeutic properties. However, its hydrophobic nature, limited solubility, and high volatility hinder the potential application of LEO in drug delivery formulations. To address these limitations, LEO nanoemulsions (LNEs) were formulated via sonication using a nonionic surfactant (Tween 80) as the emulsifier and water as the continuous medium, thereby encapsulating LEO into nanosized droplets, enhancing its solubility and bioavailability. Twelve LNEs were developed by varying oil-to-surfactant ratios (OSRs, 1:1, 1:2, and 1:3) and sonication times (5, 10, 15, and 20 min). A decrease in the average droplet diameter (Zavg) of the LNEs was observed with an increase in sonication time and a decrease in the OSR value. The optimized LNE (1:3 OSR, 20 min sonication) exhibited the smallest Zavg (12.71 nm) and showed maximum stability under centrifugation (10,000 rpm), thermal stress (30, 50, 70, and 90 °C), and long-term storage (8 weeks) with the slowest Ostwald ripening rate (ω ∼ 6.7 × 10–6 nm3 s–1). Besides, molecular dynamics simulations were conducted to evaluate the structural stability and encapsulation efficiency of LNEs at different OSRs. At 1:3 OSR, Tween 80 formed a much compact interfacial assembly around oil molecules, as reflected by lowest diffusion coefficient (D = 0.007 Å2 ps–1) and radius of gyration (Rg = 7.12 Å), indicating enhanced molecular packing and stability, consistent with experimental results. On a biological aspect, the optimized LNE exhibited enhanced in vitro anticancer activity against HCT116 colorectal cancer cells (IC50: 0.013 μL mL–1 vs 0.514 μL mL–1 for LEO) and induced apoptosis, confirmed by flow cytometry. The optimized LNE also demonstrated antibacterial activity against Escherichia coli, Bacillus cereus, Staphylococcus aureus, Salmonella typhimurium, and Vibrio cholerae with minimum inhibitory concentrations of 1.56, 2.34, 6.25, 9.38, and 6.25 μg mL–1, respectively.