Fig. 3

FeGPNPs released ferrous ions in CT26 cells to induce cell death. a Color changes in Fe²⁺ and ferrozine complexes under different conditions. I-positive control; II-pH 7.0; III-pH 7.0 + GSH 10 mM; IV-pH 4.5; V-pH 4.5 + GSH 10 mM. b Accumulated release of Fe ions (Fe²⁺ and Fe³⁺) at various pH (4.5 and 7.4) and GSH concentrations (0 and 10 mM). c CLSM images of cellular uptake of Ce6-FeGPNPs. Scale bar: 20 μm. d CLSM images of intracellular Fe²⁺ in CT26 cells after incubation with FeGPNPs. Scale bar: 20 μm. e Cytotoxicity of FeGPNPs and FePNPs against CT26 cells after 24 h of incubation. f CLSM images of dead cells with PI (red) staining. Hoechst-stained cell nucleus (blue). Scale bar: 20 μm. g GSH/GSSG ratios in FeGPNP- and FePNP-treated CT26 cells, respectively