Nanoemulsions of 1,8-cineole, and Eucalyptus globulus and Laurus nobilis essential oils: cytotoxic, antibacterial, and antioxidant activities

Antimicrobial and anticancer drug resistance is an increasing concern, driving interest in plant-based nanoformulations. Here, we developed and compared nanoemulsions containing Eucalyptus globulus essential oil (EO), Laurus nobilis EO, and their main constituent, 1,8-cineole. Gas chromatography-mass spectrometry (GC-MS) revealed 1,8-cineole content of 49.5% in E. globulus EO and 37.9% in L. nobilis EO. Nanoemulsions were prepared by spontaneous emulsification and characterized for droplet size (dynamic light scattering) and zeta potential. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy qualitatively confirmed EO encapsulation within the nanoemulsions. Average droplet sizes were 172 ± 9 nm (E. globulus EO), 92 ± 5 nm (L. nobilis EO), 137 ± 7 nm (1,8-cineole), and 70 ± 12 nm (blank nanoemulsion). The corresponding zeta potential values were - 24 ± 1.2 mV, - 34 ± 0.7 mV, - 10 ± 0.7 mV, and - 6 ± 1.5 mV. The L. nobilis EO nanoemulsion had the strongest antioxidant activity (IC₅₀ = 342 µg/mL). The E. globulus EO nanoemulsion showed the greatest cytotoxicity against A-375 human melanoma cells (IC₅₀ = 171 µg/mL) and the most potent antibacterial effects against Escherichia coli (IC₅₀ = 762 µg/mL) and Staphylococcus aureus (IC₅₀ = 205 µg/mL). These results suggest that E. globulus EO nanoemulsions have potential as antimicrobial and cytotoxic agents, pending confirmation in in vivo studies.