Finding a cancer-selective drug that avoids damaging healthy cells and organs is a holy grail in medical research. In our previous studies, gold-coated iron (Fe@Au) nanoparticles showed cancer selective anti-cancer properties in vitro and in vivo but were found to gradually lose that activity with storage or "ageing." To determine the reasons for this diminished anti-cancer activity, we examined Fe@Au nanoparticles at different preparation and storage stages by means of transmission electron microscopy combined with and energy-dispersive X-ray spectroscopy, along with X-ray diffraction analysis and cell viability tests. We found that dried and reconstituted Fe@Au nanoparticles, or Fe@Au nanoparticles within cells, decompose into irregular fragments of γ-F₂O₃ and agglomerated gold clumps. These changes cause the loss of the particles' anti-cancer effects. However, we identified that the anti-cancer properties of Fe@Au nanoparticles can be well preserved under argon or, better still, liquid nitrogen storage for six months and at least one year, respectively.
Keywords: biocompatibility; cancer; degradation; nanoparticles; zero-valent iron.