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 nano reactor 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.