Prolonged antimicrobial activity of unique sandwich-structured silver nanocomposites

In this reported work, silver (Ag) nanocomposites (NCs) with three different structures were prepared to confirm that structure has significant influence on the antibacterial properties. Ag nanoparticles (NPs) were prepared by the following three methods: first, by deposition of Ag on the surface of silica-polydopamine spheres by reducing Ag cations (NC1), secondly, by encapsulation of Ag NPs in mesoporous SiO₂ with a core-shell structure (NC2) and thirdly, Ag nanocrystals were both decorated on the surface of SiO₂ and incorporated into its mesoporous structure (NC3). The key to the successful synthesis of the aforementioned NCs was polydopamine (PD) having the unique reductive ability and powerful adhesive capability. The antibacterial activities of NC1, NC2 and NC3 were evaluated through bacterial growth curves assay carried out on Vibrio natriegens (V. natriegens) strain, a Gram-negative bacterium, supported by observations from transmission electron microscopy. The results demonstrated that in the first three days, the effect of NC1 was more intense on V. natriegens compared with NC2; however, the next seven days revealed the opposite result. Therefore NC3 exhibited the most effective antimicrobial treatments for ten days.