Eco-friendly formulations of essential oil-based silica nanocarriers as antibacterial agents

The industrial application of essential oils (EOs) is hindered by their high volatility, instability and poor solubility. Encapsulation represents an effective strategy to overcome these limitations by enhancing protection, enabling controlled release, and improving functional properties. In this study, we developed an aqueous-based sol-gel synthesis, combined with the interfacial oil miniemulsion method, to encapsulate blends of lavender (LO), thyme (TO), and cinnamon (CO) essential oils within silica nanocarriers, in order to hinder EOs volatility and instability, as well as control their release. It was also investigated whether combining LO with other essential oils (TO and CO) could provide complementary or synergistic effects. The process was conducted predominantly in water, using TEOS as silica precursor and a non-ionic surfactant under controlled conditions, aiming to reduce solvent consumption and process-related hazards in line with Safe and Sustainable by Design approach. Physicochemical characterization (SEM, FTIR, TGA, DLS, HPLC) confirmed the formation of spherical silica nanocarriers with diameters of 55-85 nm, narrow size distributions (PdI < 0.15), and encapsulation efficiencies of 93%-94%, corresponding to loading capacities of 52 wt. %. Release studies showed a sustained behavior, with release limited to 15%-26% over 48-168 h, depending on the formulation, and kinetic modelling indicated predominantly diffusion-controlled release. Antibacterial assays against Escherichia coli and Staphylococcus aureus showed that encapsulated EO blends preserved their antibacterial activity. SiO₂ nanocarriers loaded with LO showed MIC values to 25% for E. coli and 3.125% for S. aureus. Notably, the oil blends improved LO performance also within the encapsulated system, with MIC values of 6.25% and 0.78% (for LO and CO), and 6.25% and 1.56% (for LO and TO) against E. coli and S. aureus, respectively. Overall, this study demonstrates the feasibility of integrating aqueous sol-gel processing with interfacial miniemulsion to fabricate silica nanocarriers for essential oil delivery, achieving enhanced stability, controlled release behaviour, and preserved antibacterial performance, with promising implications for sustainable formulations.