This study investigated the synthesis and functional characteristics of Fe3O4@Ag core−shell nanoparticles, focusing on the impact of amino functionalization on their structural and chemical properties. Utilizing self-assembly methods driven by electrostatic interactions, we achieved the effective adsorption of Ag nanoparticles into Fe3O4 cores previously modified with silane (APTES) or polymer (PEI) precursors. Our results elucidate how the type of amino precursor affects the surface charge and subsequent adsorption dynamics, revealing that PEI-modified Fe3O4 nanoparticles exhibit more substantial Ag nanoparticle adsorption than those modified with APTES. This enhanced adsorption was attributed to the higher density of the amine groups introduced by PEI, which also affected the electrostatic properties of the nanoparticles, as evidenced by their zeta-potential values. Moreover, this study highlighted the role of electrostatic attraction in the self-assembly process, facilitating a controlled synthesis environment that enhances the stability and functionality of nanoparticles for potential biomedical and catalytic applications. This research not only advances our understanding of nanoparticle behavior under different surface chemistries but also demonstrates the importance of surface engineering in optimizing nanoparticle performance for targeted applications.