Comparison of oxidative stress response in Hep G2 cell line. (a) Two and (b) 24 h of exposure to AuNP under EMEM/S- and (c) after 24 h of exposure to EMEM/S+ assay conditions. Average values of three independent measurements are presented (mean ± SEM). Significant differences from control values are shown (*P < 0.05, **P < 0.01). α indicates significant differences between responses, as shown by pair-wise comparison analysis.