Engineered Fe3O4 nanoreactor as a high-performance hydrogen peroxide sensor

Nanozymes with peroxidase-mimicking activities have been extensively explored for hydrogen peroxide (H2O2) detection. However, the conventional nanozyme assay with suspensions suffer the limitations of restricted available surface, loss of short-lived radicals, and slow reaction in non-acidic conditions, thus have a greatly reduced detection sensitivity. We here proposed to overcome these drawbacks by constructing aligned nanoreactor sensor with Fe3O4 nanozymes distributed alongside the nanochannels of anodized aluminum oxide (termed as NR-Fe3O4), which allowed for a spatially confined nanozyme reactions (ca. 5 nm) operated under a filtration reaction mode. We presented the unique merits of NR-Fe3O4 on H2O2 detection compared to Fe3O4 nanozyme suspensions, together with the mechanism discussion about how the radical production and capturing got maximized under the confinement. As a result, our NR-Fe3O4 sensor featured a highly sensitive H2O2 detection with a linear concentration from 10 to 5000 nM (detection limit of 0.9 nM), expanded workable pH to neutral, and enhanced nanozyme stability for at least 8 h continuous run. We further showed the great feasibility of using NR-Fe3O4 sensor in complex water matrices for H2O2 detection, as it allowed for a pore rejection of background organics which in turn protected the internal radicals for a capturing and signal magnification. Our findings highlight the great interest of constructing confinement nanoreactors as an innovative approach of enhancing H2O2 detection sensitivity based on the nanozyme assay.