Applications of Magnetic Oxide Nanoparticles in Hyperthermia

Magnetic oxide nanoparticles (NPs) are probably the most common nanomaterials in everyday biomedicine, and have been in use since the 1990’s. They are usually magnetic iron oxide NPs, made of magnetite (Fe3O4 -Fe2O3), or a mixture of the two. Both of these have the spinel structure, and other spinel ferrites such as ZnFe2O4, CoFe2O4 and NiFe2O4 are also used. For applications in magnetic hyperthermia these NPs must be below the magnetic domain size, making them superparamagnetic, which means that their magnetisation can be “switched on” by the application of an external magnetic field. Magnetic hyperthermia treatment is a form of thermotherapy which is used to kill tumour cells with thermal energy (heat) in a very localised manner, by causing magnetic oxide NPs to heat up near tumour cells. Under an applied AC magnetic field the magnetic spin of the NPs switches rapidly in direction, transforming the magnetic energy into thermal energy. Temperatures of 41-46 °C are sufficient, this localised heating elevating the temperature of tumour cells, inhibiting growth, killing them, or inducing tumour cell apoptosis. Magnetic NPs were first used in tumour thermotherapy in 1996, and since then there has been a great deal of research in this field. The treatment can be applied alone, or used in combination with other therapies such as surgery, radiotherapy and chemotherapy, and it has shown excellent synergistic effects in combination with anticancer drugs (chemotherapeutics).