Impact of surface coating on the cytotoxicity of iron oxide nanoparticles in 2D and 3D mammalian cell models

Iron oxide nanoparticles (IONPs) are widely used for biomedical applications, and their nanoscale physicochemical properties and surface chemistry strongly influence biological interactions and overall performance. Their easily modified surfaces enable diverse biomedical applications, making it crucial to understand how different surfactants or coatings affect their properties and biological interactions. In this study, IONPs were synthesized by co-precipitation and subsequently functionalized with oleic acid, dextran, or ascorbic acid to investigate coating-dependent differences in physicochemical behavior and cellular responses. Comprehensive structural, magnetic, and colloidal characterizations were performed to ensure well-defined nanoparticle (NP) features. Biological evaluations included cytotoxicity assessments in both monolayer (2D) and spheroid (3D)<i>in vitro</i>models incorporating healthy and cancer-derived mammalian cell lines from different tissue origins. Direct cytotoxicity was evaluated using WST-1, resazurin, and Annexin V/propidium iodide assays, and indirect cytotoxic effects were examined using NP-conditioned media. The findings revealed that cytotoxicity varied not only with the surface coating but also with the assay format and culture model, emphasizing the need for multi-parameter assessment when evaluating NP biocompatibility. Among the tested coatings, ascorbic acid-modified IONPs exhibited the greatest reduction in hydrodynamic size (22.9 nm) and demonstrated no detectable cytotoxic effects across multiple assays and cell lines, while maintaining key magnetic characteristics. These results highlight that nanoscale surface design can be strategically leveraged to achieve a favorable balance between magnetic performance and biological safety. The study underscores the importance of coating-driven modulation in guiding the development of next-generation magnetic NPs for biomedical applications.