Glucose coated FeO@Fe₃O₄ nanoparticles show tunable catalytic reactivity and safety in a 3D hepatic in vitro model

Iron-oxide magnetic nanoparticles (MNPs) have been extensively investigated as magnetically actuated nanocatalysts for diagnostic and therapeutic applications. However, because wüstite/magnetite/maghemite phases can interconvert, coexisting Fe²⁺/Fe³⁺ species may redirect Fenton-like chemistry and generate reactive oxygen species (ROS) profiles that differ from the intended biocatalytic pathway. Here, we investigate monodisperse biphasic FeO@Fe₃O₄ core-shell MNPs with an average particle size ⟨d⟩ = 9.6(5) nm, and their glucose-coated analogue, combining EPR radical analysis with toxicity testing in a 3D HepG2 hepatic spheroid model. Naked particles exhibited conventional Fenton-like behavior dominated by hydroxyl radicals (⋅OH), whereas glucose coating markedly suppressed ⋅OH while increasing hydroperoxyl radicals (⋅OOH; ≈55 pM at 60 min), demonstrating ligand-controlled rerouting of the radical pathway. TEM mapping across spheroid cross-sections showed preferential MNP accumulation in the outer layer, with most observed events confined to the outer ≈10-15 μm, corresponding to an approximately one-cell-thick rim; sparse deeper events were observed up to ≈30-35 μm. MNPs produced dose- and time-dependent cytotoxicity in HepG2 spheroids, with IC₅₀ values of 29.3 (24 h) and 10.8 (96 h) µg·cm^- 2, without evidence of lipid peroxidation or genotoxicity. MDA levels remained unchanged, the comet assay showed no increase in DNA damage, and γH2AX and phospho-H3 (p-H3) positive events were not detected. Our results show that glucose functionalization provides a simple route to modulate radical pathways and define operational windows for redox-active FeO@Fe₃O₄ nano-reactors in oxidative nanomedicine.