## 4 Discussion
The slightly higher cytotoxicity effect of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs is explained with the restrained adsorption of the Imidazolium-PA surfactants at the initially MPA-terminated gold nanopatches. The MPA ligands apparently provided lower cell viability values for both the AuNCs and the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs. The performance of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs as X-ray dosage enhancers was compared with that of the AuNCs and Fe\({}_{3}\)O\({}_{4}\) NPs (Figures 9-11). Therefore, MCF-7, A549 and MCF-10A cells were incubated with the different kinds of nanoparticles and were exposed to X-radiation with single dosages of 1 Gy, 2 Gy, or 3 Gy. The change of the intracellular formation of ROS, in total, and the alteration of the individual O\({}_{2}\)\({}^{\bullet}\)- and HO\({}^{\bullet}\) productions were determined upon performing the DCF assay, MitoSox\({}^{\text{TM}}\)Red, and HPF assay, respectively. X-ray irradiation of the MCF-7 cells at 1 Gy significantly enhanced the ROS formation for all kinds of nanoparticles. Intracellular Fe\({}_{3}\)O\({}_{4}\)@Au pNPs increased the ROS concentration by 120%. On the other hand, the Fe\({}_{3}\)O\({}_{4}\)-NPs and AuNCs only caused increases of 85% and 60%, respectively. Intracellular Fe\({}_{3}\)O\({}_{4}\) NPs and AuNC were observed to preferentially enhance either the HO\({}^{\bullet}\) or the O\({}_{2}\)\({}^{\bullet}\) formation in MCF-7 cells only. In comparison, Fe\({}_{3}\)O\({}_{4}\)@Au pNPs elevated the concentration of both O\({}_{2}\)\({}^{\bullet}\)- and HO\({}^{\bullet}\) in MCF-7 and A549 cells, which indicates the synergistic interplay between the Fe\({}_{3}\)O\({}_{4}\) and Au surfaces for X-ray-induced ROS formation. Moreover, efficient electron transfer across the Au-Fe\({}_{3}\)O\({}_{4}\) interface potentiates the catalytic activity of the Fe\({}_{3}\)O\({}_{4}\) surface by reducing surface Fe\({}^{3+}\) to Fe\({}^{2+}\) cations [27]. The influence of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs on X-ray-induced ROS formation in the tumor MCF-7 and A549 cells was compared with that in healthy MCF-10A cells. Apparently, the ROS formation in A549 cells containing the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs reached the highest concentration increase being 140%, whereas Fe\({}_{3}\)O\({}_{4}\)@Au pNPs in X-ray irradiated MCF-10A cells enhanced ROS formation by 30% only. These results are consistent with the observed increases of the HO\({}^{\bullet}\) level in A549 and MCF-10A cells of 100% and 30%, respectively. On the other hand, the X-radiation-induced O\({}_{2}\)\({}^{\bullet}\) production in A549 and MCF-10A cells loaded with Fe\({}_{3}\)O\({}_{4}\)@Au pNPs appeared to be hardly altered. All these results indicate that the effect of Fe\({}_{3}\)O\({}_{4}\)@Au pNPs on the X-ray enhancement of the ROS production in tumor cells is considerably larger than that in healthy MCF-10A cells. The clonogenic cell survival assay was employed to survey the impact of the Fe\({}_{3}\)O\({}_{4}\) NPs, AuNC and Fe\({}_{3}\)O\({}_{4}\)@Au pNPs on the survival and proliferation of the MCF-7, A549 and MCF-10A cells exposed to X-radiation at single doses of 1, 2, and 3 Gy. In comparison with the AuNC- and Fe\({}_{3}\)O\({}_{4}\) NP-loaded tumor (MCF-7 and A549) cells, the radiation dose survival curves obtained for the cell lines containing Fe\({}_{3}\)O\({}_{4}\)@Au pNPs showed the steepest decays and the smallest DMF values, at 0.448 and 0.422, respectively. This clearly indicates higher Fe\({}_{3}\)O\({}_{4}\) surface reactivity, which is enhanced by interfacial electron transfer from the surface-grown Au nanopatches. The significantly elevated O\({}_{2}\)\({}^{\bullet}\) level in X-ray-irradiated MCF-7 cells containing Fe\({}_{3}\)O\({}_{4}\)@Au pNPs indirectly substantiates the higher concentration of Fe\({}^{2+}\) cations in the Fe\({}_{3}\)O\({}_{4}\) surface due to the reduction of Fe\({}^{3+}\) cations through interfacial Au\({}^{0}\) atoms.