ABSTRACT
Superparamagnetic iron oxides (SPIOs) including γ-Fe2O3 (maghemite) and Fe3O4 (magnetite) nanoparticles (NPs) are biocompatible and relatively easy to synthesise; these properties make them the most used magnetic nanoparticles (MNPs) in biomedicine to date. They have been studied for several decades and have contributed to both diagnostics such as magnetic resonance imaging (MRI) contrast agents and therapeutics such as magnetic hyperthermia1-4. However, the relatively low saturation magnetisation (MS) of SPIOs (∼300-400 emu·cm−3) limits their potential in these applications4,5. The response of SPIO NPs to an external magnetic šeld may be sufšcient for imaging purposes to some extent, but their suitability in magnetically targeted drug delivery is doubted, that is, they could not effectively be directed within the human body by magnetic forces because the saturation magnetisation is too low5. Enhancement of the magnetic moment of MNPs is key for improvement of many applications in biomedicine. Considering the characteristic size of biological systems, that is, 10-100 μm for a cell, 20-450 nm for a virus, 5-50 nm for a protein and 2 nm in width and 10-100 nm in length for a gene, MNPs with smaller dimensions than normally used SPIO NPs are preferred as they would increase the spatial resolution. Using MNPs, which have higher saturation magnetisation and higher magnetocrystalline anisotropy energy than SPIOs, one can signišcantly improve efšciency in various biomedical applications. Moreover, these magnetically superior ultrasmall MNPs could lead to revolutionary and novel clinical applications.
