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Spherical nanoparticles of surfactant-coated CoFe2O4(core) were prepared through thermal decomposition of metal acetylacetonates in the presence of a mixture of oleic acid and oleylamine and uniformly coated with silica shell by using tetraethylorthosilicate (TEOS) and ammonia in a micellar solution (core/shell). Transmission electron microscopy (TEM) analysis of core/shell nanoparticles evidenced the high homogeneity of the coating process in producing single core/shell nanoparticles with a narrow size distribution. The combined use of spectroscopic studies (NMR and FTIR) on core and core/shell nanoparticles pointed out that the surfactants’ layer bound to the surface core nanoparticles is retained also after the silica coating process. This allows to obtaining systems with very similar magnetic behavior but weaker dipolar interparticle interactions and lower values of saturation magnetization. In view of the interest in biomedical field, the effect of the CoFe2O4nanoparticles silica coating was also studied by controlling the possible modifications in cytotoxicity by trypan blue and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assays on human cells. [ABSTRACT FROM AUTHOR]