Fruits are safe, toxin-free, and biomolecule-rich raw
materials
that may be utilized to decrease metal ions and stabilize nanoparticles.
Here, we demonstrate the green synthesis of magnetite nanoparticles
which were first capped with a layer of silica, followed by the decoration
of silver nanoparticles, termed Ag@SiO2@Fe3O4, by using lemon fruit extract as the reducing agent in a
size range of ∼90 nm. The effect of the green stabilizer on
the characteristics of nanoparticles was examined via different spectroscopy
techniques, and the elemental composition of the multilayer-coated
structures was verified. The saturation magnetization of bare Fe3O4nanoparticles at room temperature was recorded
as 78.5 emu/g, whereas it decreased to 56.4 and 43.8 emu/g for silica
coating and subsequent decoration with silver nanoparticles. All nanoparticles
displayed superparamagnetic behavior with almost zero coercivity.
While magnetization decreased with further coating processes, the
specific surface area increased with silica coating from 67 to 180
m2g–1and decreased after the addition
of silver and reached 98 m2g–1, which
can be explained by the organization of silver nanoparticles in an
island-like model. Zeta potential values also decreased from −18
to −34 mV with coating, indicating an enhanced stabilization
effect of the addition of silica and silver. The antibacterial tests
againstEscherichia coli(E. coli) andStaphylococcus aureus(S. aureus) revealed that the bare
Fe3O4and SiO2@Fe3O4did not show sufficient effect, while Ag@SiO2@Fe3O4, even at low concentrations (≤ 200 μg/mL),
displayed high antibacterial activity due to the existence of silver
atoms on the surface of nanoparticles. Furthermore, the in vitro cytotoxicity
assay revealed that Ag@SiO2@Fe3O4nanoparticles were not toxic to HSF-1184 cells at 200 μg/mL
concentration. Antibacterial activity during consecutive magnetic
separation and recycling steps was also investigated, and nanoparticles
offered a high antibacterial effect for more than 10 cycles of recycling,
making them potentially useful in biomedical fields.