Novel core-shell nanocomposites based on TiO₂ -covered magnetic Co₃ O₄ for biomedical applications

Magnetic Co₃ O₄ nanoparticles (NPs) have great potential for applications in biomedicine, as contrast enhancement agents for magnetic resonance imaging, or for drug delivery. Although these NPs are so attractive, their potential toxicity raises serious questions about decreasing cellular viability. In this context, Co₃ O₄ NPs were prepared via sol-gel method and encapsulated with a layer of TiO₂ , a biocompatible oxide, and subjected to structural, magnetic and toxicity characterization. X-ray diffractograms of the samples demonstrate the successful synthesis of the spinel and Raman spectroscopy confirms the coating of the Co₃ O₄ spinel with TiO₂ . The Co₃ O₄ cores showed a very intense superparamagnetic character; however, this behavior is strongly suppressed when the material is covered with TiO₂ . According to the neutral red uptake assay, the coating of the cores with TiO₂ significantly decreases the cytotoxic character of the Co₃ O₄ particles and, as it can be observed with the zeta (ξ) potential measurements, they form a stable colloidal dispersion at cytoplasmic pH. The effect of the thermal treatment enhances the biocompatibility even further, with no statistically significant effect on cell viability even at the highest analyzed concentration. The proposed pathway presents a successful sol-gel method for the preparation of Co₃ O₄ @TiO₂ core-shell nanoparticles. This work opens up possibilities for future application of these materials not only for magnetic resonance imaging but also in catalysis and hyperthermia.