Template-free construction of hollow mesoporous Fe₃O₄ nanospheres as controlled drug delivery with enhanced drug loading capacity

Monodisperse hollow mesoporous Fe₃O₄ nanospheres have been successfully synthesized via a template-free one-pot solvothermal method under the existence of iron chloride hexahydrate, polyvinylpyrrolidone and urea. A proposed gas-bubble-assisted Ostwald ripening mechanism was allowed to explain the possible fabrication of hollow nanostructures. The formed Fe₃O₄ nanospheres possessed a narrow particle size distribution with a average hydrodynamic diameter of 392 nm, superparamagnetic characteristics with high saturation magnetization of 74.9 emu/g, as well as the typical mesoporous structures with specific surface area of 27.3 m²/g. Furthermore, it was found that the bare hollow mesoporous Fe₃O₄ nanospheres showed an insignificant cytotoxicity, but exhibited obvious cytotoxic effects towards HeLa cells after being loaded with the anti-cancer drug of DOX, which could be recommended as a promising and effective drug delivery system with high drug loading capacity and pH-responsive feature. The determined maximum drug loading capacity of DOX on this kind of hollow mesoporous Fe₃O₄ nanospheres was as high as 0.36 ± 0.04 g/g, which can store and deliver effectively the anticancer drugs to induce death of cancer cells.