Uptake studies of SDIO–DO3A by J774 macrophages and cytotoxicity study on HepG2 cells at 37 °C. (a) Uptake studies of SDIO–DO3A at different iron concentrations at 37 °C. Mean T2 values of J774 cell lysates incubated with SDIO–DO3A nanoparticles for 1 h are presented. *, P < 0.001; &, P = 0.002; #, P = 0.01–0.02. (b) Competition uptake of SDIO–DO3A-10 (100 μM [Fe]) by J774 with the presence of competitor (dextran or dextran sulfate) at 37 °C. (c) Cell viability studies with C12-resazurin assay. HepG2 cells were incubated for 4, 24, and 48 h with different iron concentrations of SDIO–DO3A-10. Fluorescent intensities reflecting survival fractions were normalized against the signal from the untreated cells. All error bars present SEM (n = 3).