Silver-Decorated and Silica-Capped Magnetite Nanoparticles with Effective Antibacterial Activity and Reusability

Fruits are safe, toxin-free, and biomolecule-rich rawmaterialsthat may be utilized to decrease metal ions and stabilize nanoparticles.Here, we demonstrate the green synthesis of magnetite nanoparticleswhich were first capped with a layer of silica, followed by the decorationof silver nanoparticles, termed Ag@SiO2@Fe3O4, by using lemon fruit extract as the reducing agent in asize range of similar to 90 nm. The effect of the green stabilizer onthe characteristics of nanoparticles was examined via different spectroscopytechniques, and the elemental composition of the multilayer-coatedstructures was verified. The saturation magnetization of bare Fe3O4 nanoparticles at room temperature was recordedas 78.5 emu/g, whereas it decreased to 56.4 and 43.8 emu/g for silicacoating and subsequent decoration with silver nanoparticles. All nanoparticlesdisplayed superparamagnetic behavior with almost zero coercivity.While magnetization decreased with further coating processes, thespecific surface area increased with silica coating from 67 to 180m(2) g(-1) and decreased after the additionof silver and reached 98 m(2) g(-1), whichcan be explained by the organization of silver nanoparticles in anisland-like model. Zeta potential values also decreased from -18to -34 mV with coating, indicating an enhanced stabilizationeffect of the addition of silica and silver. The antibacterial testsagainst Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) revealed that the bareFe(3)O(4) and SiO2@Fe3O4 did not show sufficient effect, while Ag@SiO2@Fe3O4, even at low concentrations (<= 200 mu g/mL),displayed high antibacterial activity due to the existence of silveratoms on the surface of nanoparticles. Furthermore, the in vitro cytotoxicityassay revealed that Ag@SiO2@Fe3O4 nanoparticles were not toxic to HSF-1184 cells at 200 mu g/mLconcentration. Antibacterial activity during consecutive magneticseparation and recycling steps was also investigated, and nanoparticlesoffered a high antibacterial effect for more than 10 cycles of recycling,making them potentially useful in biomedical fields.

Automated summary

Fruit extracts were used to synthesize silver-decorated magnetite nanoparticles with a silica coating. The nanoparticles exhibited decreased magnetization with subsequent coating processes, but increased specific surface area with silica coating. The addition of silver atoms on the surface of the nanoparticles resulted in high antibacterial activity against E. coli and S. aureus. The nanoparticles also showed no cytotoxicity to cells and maintained antibacterial activity during consecutive magnetic separation and recycling.