Effect of Co-Fe NPs on viability assayed by MTT. Cytotoxicity was examined in different cultured cells: (A) Caco-2, (B) HepG2, (C) MDCK, (D) A459, (E) NCIH441, (G) TK6 and in lung slices (F). Cells were treated with 0 – 1.2 mM Co-Fe NPs for 24 and 72 h. Cell viability was assessed by MTT assays and results are presented as ratio of control (untreated group). Mean ± SD of three independent experiments performed in triplicate. * Significant differences of each point from the control at P<0.05.