Fe0/Fe3C-assisted Fe3O4 redox sites as robust peroxidase mimics for colorimetric detection of H2O2

Fe-based nanozymes have been shown promising peroxidase-mimicking activity and are used as colorimetric H2O2 sensing platforms. However, the redox cycle of Fe2+/Fe3+ in the Fe-H2O2 system to generate •OH that is needed to oxidize chromogenic substrate (3, 3′, 5, 5′-tetramethylbenzidine, TMB) is restricted due to a slower reaction rate of Fe3+ with H2O2 which leads to insensitive colorimetric detection of H2O2. In this study, Fe3O4-Fe0/Fe3C nanozyme was processed with a peculiar peroxidase-mimicking activity from a carbothermal reduction of ZnFe-double-layer hydroxide and glucose-derived carbon under a nitrogen environment. The nanozyme Fe3O4-Fe0/Fe3C was engineered upon thermal treatment and its peroxidase-mimicking activity was studied in detail. The Fe3O4-Fe0/Fe3C nanozyme exhibits excellent peroxidase activity with regard to the activation of H2O2 and oxidation of TMB due to the synergy of Fe3O4 and Fe0/Fe3C interface. A Fe0/Fe3C improves Fe2+/Fe3+ redox chemistry, and electron transfer kinetics to generate sufficient •OH while strong Lewis acid property of Fe3+ enhances adsorption of TMB. This synergy leads Fe3O4-Fe0/Fe3C nanozyme for highly selective and supersensitive sensing of H2O2 with a low limit of detection (67.1 pM). Furthermore, the proposed colorimetric sensor was impressively used for the real-time detection of H2O2 in milk and HepG2 living cells with excellent biocompatibility.