Synthesis of Silica-Coated Silver-Cobalt Ferrite Nanoparticles for Biomedical Applications

In this work, a series of silver-substituted cobalt ferrite (Ag_xCo_1-xFe₂O₄, 0 ≤ x ≤ 0.1) nanoparticles (NPs) were synthesized, and then a sample with monophase structure and optimum magnetic properties was coated with an amorphous silica layer. First, Ag-substituted Co-ferrite NPs were synthesized via a sol-gel auto combustion method from aqueous metal nitrates solutions. Then, all the powders were characterized by several techniques such as X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), and vibrating sample magnetometry (VSM). These results showed that when the Ag content was between 0 and 0.08, the synthesized powders were the cubic spinel structure, having spherical-shaped particles with an average size of about 20–25 nm. Afterward, the silica coating was applied on the surfaces of the selected sample (i.e., Ag_0.08Co_0.92Fe₂O₄ NPs with monophase structure and optimum magnetic properties) by a sol-gel approach based on the Stöber process from the tetraethyl orthosilicate (TEOS) as the precursor of silica. Transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, and zeta potential investigations were used to study the characteristics of the silica-coated Ag-Co-ferrite NPs. The results of FTIR and TEM analyses confirmed the presence of the silica coating on the surfaces of the Ag-Co-ferrite NPs. Although the silica-coated sample showed the saturation magnetization (M_S) value slightly lower than that of the uncoated one, however, its magnetic properties are suitable for use in different biomedical applications. Also, a water-based suspension containing the silica-coated Ag-Co-ferrite NPs showed a more negative zeta potential value at the pH of 7 in comparison with a suspension containing uncoated ones. Therefore, it can be concluded that the synthesized silica-coated Ag_0.08Co_0.92Fe₂O₄ NPs in this study could be considered as a good candidate for the preparation of biomedical ferrofluids.