Essential oil–encapsulated SiO ₂ nanocapsules for the treatment of bacterial biofilms formed on food‐contact surfaces

Litsea cubeba essential oil (EO)-encapsulated SiO₂ (SiO₂-EO) nanocapsules were fabricated by in situ biosilicification for the treatment of biofilms on food-contact surfaces. By optimizing the synthesis conditions (0.5 mg/mL EO and 50 mM silicic acid), SiO₂-EO nanocapsules exhibited a uniform size distribution (150-200 nm) with a distinct core-shell structure. The characterization of nanocapsules was elucidated using a scanning electron microscope (SEM), transmission electron microscope, Fourier transform infrared, and x-ray diffraction analyses. The minimal inhibitory concentrations of SiO₂-EO nanocapsules were 5 and 1.25 mg/mL for Escherichia coli and Staphylococcus aureus, respectively. Compared to free EO, the SiO₂-EO nanocapsules showed more significant inhibition activity against both Gram-negative and Gram-positive bacterial biofilms. Confocal experiments and SEM demonstrated that the nanocapsules efficiently penetrate biofilms within 30 min and deliver EO to destroy the membrane structure of bacteria. Eventually, SiO₂-EO nanocapsules were also applied to four kinds of food-contact surfaces. The populations in biofilms exposed to 2.5 mg/mL of nanocapsules decreased 1.51-1.56 log CFU/cm² and 2.15-2.22 log CFU/cm² for E. coli and S. aureus, respectively. This study provides an innovative strategy to treat bacterial biofilms with EO-based nanocomposites.