Effect of Co-Fe NPs on viability assayed by NR. Cytotoxicity was examined in different cultured cells: (A) Caco-2, HepG2 (B) and (C) MDCK. Cells were treated with 0 – 1.2 mM Co-Fe NPs for 24 and 72 h. Cell Viability was assessed by NR 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.