Structural effect of Fe₃O₄ nanoparticles on peroxidase-like activity for cancer therapy

Ferromagnetic nanoparticles (Fe₃O₄ NPs) have been proven to have the intrinsic peroxidase-like activity. This property has been used for analyte detection, tumor tissue visualization, and cancer therapy, etc. However, the effect of particle structure and morphology on its peroxidase-like activity has been rarely reported. In this work, we fabricated Fe₃O₄ nanoparticles with different structures (nanoclusters, nanoflowers, and nanodiamonds) by facilely tuning the pH values in the hydrothermal reaction. Their in vitro peroxidase-like activity was evaluated via chromogenic reaction of 3,3',5,5'-tetramethylbenzidine (TMB) by the reduction of H₂O₂ to H₂O. It was found the nanostructures had a great influence on their peroxidase-like activity, following the order of nanoclusters>nanoflowers>nanodiamonds. With this activity, the peroxidase-like activity of Fe₃O₄ NPs was used for cancer therapy with the addition of low-concentration H₂O₂. The cancer cell-killing activity was due to the intracellular generated reactive oxygen species (ROS) after endocytosis of Fe₃O₄ NPs into the Hela cells. It was interesting that the cell killing ability of these three kinds of Fe₃O₄ NPs was not consistent with the in vitro enzyme-like activity. It was deduced that the cell endocytosis of the nanoparticles along with their enzyme-like activity co-determined their cancer cell-killing performance.