Recyclable magnetite-silver heterodimer nanocomposites with durable antibacterial performance

There is a significant need for magnetite-silver nanocomposites that exhibit durable and recyclable antimicrobial activity. In this study, magnetic iron oxide nanoparticles (Fe₃O₄ NPs) coated with ethylenediamine-modified chitosan/polyacrylic acid copolymeric layer (Fe₃O₄@ECS/PAA) were fabricated. Subsequently, directly deposited silver (Ag) NPs procedure was carried out to form the antibacterial heterodimers of Fe₃O₄@ECS/PAA-Ag NPs. The composition and morphology of the resultant nanostructures were confirmed by FT-IR, XRD, TEM and TGA. The overall length of the heterodimers was approximately 45 nm, in which the mean diameter of Fe₃O₄@ECS/PAA NPs reached up to 35 nm, and that of Ag NPs was around 15 nm. The mass fraction of silver NPs in the nanocomposites was about 63.1%. The obtained Fe₃O₄@ECS/PAA NPs exhibited good colloidal stability, and excellent response to additional magnetic field, making the NPs easy to recover after antibacterial tests. In particular, the Fe₃O₄@ECS/PAA-Ag NPs retained nearly 100% biocidal efficiency (10⁶-10⁷ CFU/mg nanoparticles) for both Gram-negative bacteria E. coli and Gram-positive bacteria S. aureus throughout ten cycles without washing with any solvents or water, exhibiting potent and durable antibacterial activity.