## 3 Results
Apparently, the TEM image of the MCF-7 cell reveals that Fe\({}_{3}\)O\({}_{4}\)@Au pNPs formed large agglomerates (black spots) within the cytoplasm. These agglomerates were entrapped in cellular vesicles (endosomes) which indicates cellular uptake via endocytosis. The biocompatibility of the Imidazolium-PA-terminated Fe\({}_{3}\)O\({}_{4}\)@Au pNPs was compared with those of Imidazolium-PA-terminated Fe\({}_{3}\)O\({}_{4}\) NPs and MPA-stabilized gold nanoclusters (AuNCs) upon examining their influence on the viability of tumor cells (MCF-7 and adenocarcinoma human alveolar basal epithelial (A459) cells) and healthy cells (human breast epithelial cell line (MCF-10A)) (Figure 8). Figure 6: FTIR transmission spectra of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs and the structure formula of the surfactants MPA (**top right**) and Imidazolium-PA (**bottom right**). Figure 7: TEM image of an MCF-7 cell loaded with Fe\({}_{3}\)O\({}_{4}\)@Au pNPs. The respective cell viability data in Figure 8 were obtained by conducting the neutral red assay. The dashed line at 100% represents the viability of the respective control cells. Fe\({}_{3}\)O\({}_{4}\)@Au pNPs at a concentration of 10 \(\mu\)g/mL were found to decrease the viability of MCF-7 and MCF-10A cells down to 80%, whereas the A549 cells were hardly impaired. Intracellular AuNCs were found to diminish the viability of all cell lines under study by 10 to 13%. In contrast, the biocompatibility of the Imidazolium-PA-stabilized Fe\({}_{3}\)O\({}_{4}\) NPs is remarkably high, exhibiting cell viability values of around 95% for the MCF-7, MCF-10A and A549 cells. This is explained by the shielding effect of Imidazolium-PA, which is self-assembled in a monolayer on the Fe\({}_{3}\)O\({}_{4}\) NP surface, obviously preventing the formation of HO\({}^{\bullet}\) at the Fe\({}^{2+}\) cation-containing surface. The slightly toxic effect of the MPA-ligands apparently provided a lower cell viability value for the AuNC and Fe\({}_{3}\)O\({}_{4}\)@Au pNPs. To examine the impact of the Fe\({}_{3}\)O\({}_{4}\)@Au pNPs on X-ray-induced formation of the intracellular formation of reactive oxygen species (ROS), MCF-7, A549 and MCF-10A cells were incubated with Fe\({}_{3}\)O\({}_{4}\) NPs, AuNC or Fe\({}_{3}\)O\({}_{4}\)@Au pNPs and subsequently exposed to X-radiation at a single dose of 1 Gy (Figures 9 and 10). The change of the intracellular formation of ROS, in total, as well as that of superoxide anion radical (O\({}_{2}\)\({}^{\bullet}\)) or hydroxyl radical (HO\({}^{\bullet}\)), in particular, were quantified using the dichlorofluorescein (DCF) assay, mitochondrial superoxide indicator MitoSox\({}^{\text{TM}}\)Red, and the 3'-(p-hydroxyphenyl)-fluorescein (HPF) assay, respectively. Whereas MCF-7 cells loaded with Fe\({}_{3}\)O\({}_{4}\) NPs or AuNC did not exhibit any change of ROS and HO\({}^{\bullet}\) formation, intracellular Fe\({}_{3}\)O\({}_{4}\)@Au pNPs apparently raised the ROS and HO\({}^{\bullet}\) levels by 40 and 10%, respectively (Figures 9a and 10a). All kinds of nanoparticles were observed to boost the relative O\({}_{2}\)\({}^{\bullet}\)- concentration by 30 to 40% (Figure 9b). These results are consistent with the cell viability study (Figure 8) and confirm the highest biocompatibility for the Imidazolium-PA-terminated Fe\({}_{3}\)O\({}_{4}\) NPs. X-ray exposure of the MCF-7 cells at a single dose of 1 Gy resulted into a significant enhancement of the ROS formation for all kinds of nanoparticles. While intracellular Fe\({}_{3}\)O\({}_{4}\)@Au pNPs provided an increase of the ROS concentration by 120%, the Fe\({}_{3}\)O\({}_{4}\)-NPs and AuNC caused an increase of 85% and 60%, respectively (Figure 9a). On the other hand, X-ray irradiation of MCF-7 cells loaded with Fe\({}_{3}\)O\({}_{4}\) NPs provoked O\({}_{2}\)\({}^{\bullet}\) degradation by 20%, which probably occurs through the X-ray-activated Fe\({}_{3}\)O\({}_{4}\) surfaces as requiring H\({}_{2}\)O\({}_{2}\) and O\({}_{2}\)\({}^{\bullet}\)-consumption during the [PERSON] and Haber-Weiss reaction (Figure 10b).