###### Abstract
On the one hand, the magnetic properties allow for the nanoparticles to be guided to the tumor site using an external magnetic field [14; 15; 16]. On the other hand, the silver coating can potentially enhance the cytotoxic effects on cancer cells through generation of reactive oxygen species and disruption of cellular processes [17]. To fully harness the potential of Fe\({}_{3}\)O\({}_{4}\)-Ag decorated nanoparticles in biomedical applications, it is crucial to understand their cytotoxicity and biocompatibility in relevant cell lines. Human fibroblasts (HFF-1) and breast cancer cells (MCF-7) serve as important model systems for evaluating the biological impact of these nanoparticles, as they represent crucial components of the human body -healthy cells and cancer cells, respectively [18; 19; 20]. Regarding to the obtention of these magnetoplasmonic structures, the synthesis of Fe\({}_{3}\)O\({}_{4}\)-Ag decorated nanoparticles can be achieved through various chemical and biological methods [9]. Typically, the core Fe\({}_{3}\)O\({}_{4}\) nanoparticles are first prepared, followed by the deposition of silver onto the surface. several synthesis methods of Fe\({}_{3}\)O\({}_{4}\)-Ag nanoparticles have been reported, such as co-precipitation, thermal decomposition, microemulsion, and green synthesis approaches using plant extracts or microbial agents [16; 21; 22]. Recently, green synthesis methods have gained attention due to their eco-friendly nature and the potential to produce biocompatible nanoparticles [23; 24]. For example, the use of deep eutectic solvents as reducing and stabilizing agents in the synthesis of Fe\({}_{3}\)O\({}_{4}\)-Ag nanoparticles has been reported [25; 26]. However, the Chemical reduction is one of the most widely used methods for the synthesis of these nanostructures, as it allows for precise control over the size, morphology, and composition of the nanoparticles [16; 27; 28]. The formation of the silver shell or decorated on the Fe\({}_{3}\)O\({}_{4}\) core can be achieved through the reduction of silver nitrate (AgNO\({}_{3}\)) in the presence of a reducing agent, such as sodium borohydride or ascorbic acid [29]. The resulting Fe\({}_{3}\)O\({}_{4}\)-Ag nanoparticles can be further functionalized with various biomolecules, polymers, or drug compounds to enhance their biocompatibility, targeting, and therapeutic capabilities [30; 31]. In this sense, evaluating the cytotoxic effects of Fe\({}_{3}\)O\({}_{4}\)-Ag decorated nanoparticles is important to deepen knowledge of their biosecurity for their future biomedical applications. This research used the human HFF-1 fibroblast cell line as a model for non-cancerous epithelial cells, often employed to determine nanoparticles' overall biocompatibility and safety [32]. Meanwhile, MCF-7 cells were employed as a well-established model for breast cancer, specifically representing the luminal subtype. Thus, ref. [32] evaluating the cytotoxicity of Fe\({}_{3}\)O\({}_{4}\) and Fe\({}_{3}\)O\({}_{4}\)-Ag nanoparticles in both types of cells can provide insights into their potential toxic effects, which is crucial for their development as safe and effective future biomedical agents. On the other hand, breast cancer cell lines, such as MCF-7, are used to assess the anticancer potential of Fe\({}_{3}\)O\({}_{4}\)-Ag nanoparticles. The ability of these nanoparticles to selectively induce cytotoxicity in cancer cells while sparing healthy cells is a desirable characteristic for their future application in cancer therapy [25; 29]. The cytotoxicity studies typically involve exposing the cell lines to varying concentrations of the Fe\({}_{3}\)O\({}_{4}\)-Ag nanoparticles and evaluating their effects on cell viability, proliferation, and morphology using various assays, such as MTT, LDH, or live/dead staining.