Objectives: A colloidal suspension of superparamagnetic iron oxide nanoparticles (SPION) with an average particle size of 6 nm was prepared for further surface modification with gold and L-aspartic acid (LAA). The information about the cytotoxicity and endocytosis was provided by in vitro studies of human fibroblast response to the particles.
Methods: XRD, TEM, FT-IR, SQUID, alongside light and fluorescence microscopy were used to characterize the samples.
Results: The XRD spectra of all samples exhibit a pure magnetite phase. TEM images demonstrate that particles have almost spherical morphology with a mean diameter of 12 and 9 nm for Au@SPION and LAA@SPION, respectively. FT-IR data confirm the presence of LAA on the surface of particles. Uncoated SPION demonstrate superparamagnetic behaviour with reduced value of saturation magnetization for Au@SPION and LAA@SPION. Incubation of particles with human fibroblasts for 24 hrs shows similar gross cell morphologies to control cells. Clathrin staining displays an increase in clathrin production, particularly at the cell filopodia.
Conclusions: The cells incubated with Au@SPION and LAA@SPION are definitely responding to the particles. Au@SPION appears to be internalized by the cells through endocytosis. LAA@SPION shows partial endocytosis, and there is no cytoskeletal disorganization and no cell damage.

Keywords: Nanoparticles, Endocytosis, Magnetite, Superparamagnetism, Human Fibroblasts, toxicity, Cytoskeleton