Solvothermal synthesis of cobalt ferrite nanoparticles loaded on multiwalled carbon nanotubes for magnetic resonance imaging and drug delivery

Multiwalled carbon nanotube (MWCNT)/cobalt ferrite (CoFe₂O ₄) magnetic hybrids were synthesized by a solvothermal method. The reaction temperature significantly affected the structure of the resultant MWCNT/CoFe₂O₄ hybrids, which varied from 6 nm CoFe ₂O₄ nanoparticles uniformly coated on the nanotubes at 180 °C to agglomerated CoFe₂O₄ spherical particles threaded by MWCNTs and forming necklace-like nanostructures at 240 °C. Based on the superparamagnetic property at room temperature and high hydrophilicity, the MWCNT/CoFe₂O₄ hybrids prepared at 180 °C (MWCNT/CoFe₂O₄-180) were further investigated for biomedical applications, which showed a high T₂ relaxivity of 152.8 Fe mM^-1 s^-1 in aqueous solutions, a significant negative contrast enhancement effect on cancer cells and, more importantly, low cytotoxicity and negligible hemolytic activity. The anticancer drug doxorubicin (DOX) can be loaded onto the hybrids and subsequently released in a sustained and pH-responsive way. The DOX-loaded hybrids exhibited notable cytotoxicity to HeLa cancer cells due to the intracellular release of DOX. These results suggest that MWCNT/CoFe₂O₄-180 hybrids may be used as both effective magnetic resonance imaging contrast agents and anticancer drug delivery systems for simultaneous cancer diagnosis and chemotherapy.