## 3 Results and Discussion
### X-ray Photoelectron Spectroscopy (XPS) Analysis  
X-ray photoelectron spectroscopy (XPS) analysis was conducted to ascertain the electronic structures or valence states of Fe\({}_{3}\)O\({}_{4}\)-Ag nanoalloys. Figure 5a depicts the analysis spectra of the Fe\({}_{3}\)O\({}_{4}\)-Ag nanostructures. Within these spectra, the signals of Fe 2p, O 1s, and Ag 3d are discernible as principal components of the acquired nanoparticles [49; 50]. Figure 5b illustrates the Ag 3d region, wherein the Ag d5/2 and Ag d2/3 orbitals are fully identifiable at 368.3 and 374.3 eV, respectively [50], serving as compelling evidence corroborating the presence of Ag as a constituent element of the Fe\({}_{3}\)O\({}_{4}\)-Ag nanostructures, as indicated in the preceding characterization results from scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS). Figure 5: XPS Spectra of Fe\({}_{3}\)O\({}_{4}\)-Ag Decorated Nanostructures: (**a**) Survey Spectra, (**b**) HR-XPS of Fe 2p, (**c**) O 1s, and (**d**) Ag 3d. Additionally, the binding energies of Fe 2p1/2 and Fe 2p3/2 were identified at 724.9 and 711.6 eV, respectively, values associated with the spin-orbit peaks of Fe\({}_{3}\)O\({}_{4}\) (Figure 5c). An energy separation of 13.9 eV between Fe 2p (1/2) and Fe 2p3/2 was observed, a value specifically reported for the core level signal of Fe\({}_{3}\)O\({}_{4}\). Related satellite peaks at 719.4 eV and 733.5 eV were also discerned [51]. Finally, Figure 5d reveals a high-resolution X-ray photoelectron spectrum (HRXPS) of the O1(s) orbital, with a binding energy identified at 530.74 eV, associated with the oxygen of Fe\({}_{3}\)O\({}_{4}\). These results collectively serve as evidence of the formation of Fe\({}_{3}\)O\({}_{4}\)-Ag nanostructures [52]. Cell Viability of Fe\({}_{3}\)O\({}_{4}\) and Fe\({}_{3}\)O\({}_{4}\)-Ag Decorated Nanoparticles on Human Fibroblast (HFF-1) and Breast Cancer Cells (MCF-7)  
To analyze whether the Fe\({}_{3}\)O\({}_{4}\) and Fe\({}_{3}\)O\({}_{4}\)-Ag decorated nanoparticles induce a cytotoxic effect, cell viability test was performed on HFF-1 human fibroblasts and MCF-7 human breast cancer cells. As observed in Figure 6a, the cell viability on HFF-1 fibroblasts changed across the different concentrations of Fe\({}_{3}\)O\({}_{4}\) and Fe\({}_{3}\)O\({}_{4}\)-Ag decorated nanoparticles. However, none of them significantly reduced cell viability; thus, all the concentrations tested were not cytotoxic. On the other hand, the cell viability of MCF-7 breast cancer cells did not change upon the exposure of cells to different concentrations of nanoparticles, indicating that all of them are compatible and allowed the cells to grow as in the control (Figure 6b). These results indicate that Fe\({}_{3}\)O\({}_{4}\) and Fe\({}_{3}\)O\({}_{4}\)-Ag nanoparticles are not toxic. However, it is essential to ensure that these nanoparticles do not exhibit undesirable cytotoxicity towards normal non-cancerous cells, as this could limit their viability and safety for clinical use [51; 53]. Unlike our study, which focused on comparing the cytotoxic effects of Fe\({}_{3}\)O\({}_{4}\) and Fe\({}_{3}\)O\({}_{4}\)@Ag NPs, other studies have evaluated similar nanosystems conjugated with thiolated chitosan in different cell lines such as HFF-1 fibroblasts, MC3T3-E1 osteoblasts, and the osteosarcoma cell line MG63. These studies used higher concentrations ranging from 5 to 200 ug/mL. Specifically, in HFF-1 cells, a 50% decrease in cell viability was observed starting from 100 ug/mL [54]. Careful evaluation of the effects of nanoparticles on cancerous and non-cancerous cell lines at various concentrations is essential to achieve the appropriate balance between therapeutic efficacy and biocompatibility [55]. Figure 6: Cell viability assay of Fe\({}_{3}\)O\({}_{4}\) and Fe\({}_{3}\)O\({}_{4}\)-Ag decorated nanoparticles on (**a**) human fibroblast (HFF-1), and (**b**) breast cancer (MCF-7) cells.