Intriguingly, our previous research demonstrated that Fe@Au showed cancer-preferential cytotoxicity toward oral cancer in vitro and in vivo, which was caused by the nonoxidized iron in the nanoparticles.17 Furthermore, we determined that the nanoparticles caused their cytotoxic effect in OECM1 through mitochondria-mediated autophagy.18 Similarly, Thurber et al19 have demonstrated that Fe doping of ZnO nanoparticles improved their ability to selectively kill leukemia cells. They suggested that pure iron possesses potential as a cancer-selective anticancer agent, in accordance with our results.