Ag-decorated Fe3O4@SiO2 core-shell nanospheres: Seed-mediated growth preparation and their antibacterial activity during the consecutive recycling

• Ag-decorated Fe3O4@SiO2 were synthesized via a seed-mediated growth method.
• The core-shell heterostructures exhibited excellent antibacterial activity.
• The activity was attributed to the effect of released Ag+ with ROS oxidation.
• The antibacterial agent was reused during magnetic separation and recycling.

We demonstrated a seed-mediated growth approach to synthesize Ag nanoparticles-decorated Fe3O4@SiO2 core-shell nanospheres without use of surface functionalization. The particle size and decoration density of the immobilized Ag nanoparticles on SiO2 surface were tunable by adjusting the added AgNO3 concentration and the alternating repetition times in seed-mediated growth procedure. The as-prepared Ag-decorated Fe3O4@SiO2 nanospheres exhibited excellent antibacterial activities against Escherichia coli, Bacillus subtilis and Candida albicans, in which the minimum inhibitory concentration were 12.5 μg mL−1, 50 μg mL−1 and 50 μg mL−1, respectively. It is speculated that their antibacterial activity is attributed to both the interaction of released Ag ions with the functional groups of vital enzymes and proteins and the strong oxidation of reactive oxygen species generated under the action of photoinduced electrons in Ag nanoparticles. Besides studying their antibacterial mechanism, we also investigated the variation of antibacterial activity of these heterostructured nanospheres during the consecutive magnetic separation and recycling. It shows that the magnetic antibacterial agent could be reused and its activity remained stable even after nine cycles, which enable it to be promisingly applied in biomedical areas.

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