Antibacterial Silver-Conjugated Magnetic Nanoparticles: Design, Synthesis and Bactericidal Effect

The aim was to design and thoroughly characterize monodisperse Fe₃O₄@SiO₂-Ag nanoparticles with strong antibacterial properties, which makes them a candidate for targeting bacterial infections.

The monodisperse Fe₃O₄ nanoparticles were prepared by oleic acid-stabilized thermal decomposition of Fe(III) oleate; the particles were coated with silica shell using a water-in-oil reverse microemulsion, involving hydrolysis and condensation of tetramethyl orthosilicate. Resulting Fe₃O₄@SiO₂ particles were modified by (3-mercaptopropyl)trimethoxysilane to introduce 1.1 mmol SH/g. Finally, the Fe₃O₄@SiO₂-SH nanoparticles were decorated with silver nanoclusters formed by reduction of silver nitrate with NaBH₄. The particles were analyzed by FTIR, X-ray photoelectron and atomic absorption spectroscopy, dynamic light scattering and vibrating sample magnetometry. The antibacterial activity of the Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂-Ag nanoparticles was tested against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli bacteria cultivated on Luria agar plates or in Luria broth.

The superparamagnetic Fe₃O₄@SiO₂-Ag nanoparticles (21 nm in diameter; saturation magnetization 26 A∙m²/kg) were successfully obtained and characterized. Inhibitory and toxic effects against bacteria were documented by incubation of the Fe₃O₄@SiO₂-Ag nanoparticles with Staphylococcus aureus and Escherichia coli.

The combination of magnetic properties together with bactericidal effects is suitable for the disinfection of medical instruments, water purification, food packaging, etc.