Peroxidase mimetic activity of porphyrin modified ZnFeO/reduced graphene oxide and its application for colorimetric detection of HO and glutathione.

Artificial nanoenzymes which can overcome some drawbacks of natural enzymes is a challenging topic in the biosensor field. Herein, we demonstrated 5, 10, 15, 20-tetrakis (4-carboxylpheyl)-porphyrin modified magnetic ZnFeO nanoparticles loaded on the surface of reduced graphene oxide (Por-ZnFeO/rGO), which exhibited intrinsic peroxidase-like activity and rapidly oxidized the peroxidase substrate 3, 3', 5, 5'-tetramethylbenzidine (TMB) into a blue product (OxTMB) distinguished by naked eyes. Interestingly, by comparative study of different nanomaterials ZnFeO nanoparticles, ZnFeO/rGO and Por-ZnFeO, Por-ZnFeO/rGO was proved to possess the highest peroxidase-like activity. Electron spin resonance (ESR) verified the catalytic activity of Por-ZnFeO/rGO for HO was due to hydroxyl radical from decomposition of HO. Temperature and pH strongly affected the peroxidase-like activity of Por-ZnFeO/rGO nanocomposites. Under optimal conditions (pH = 4, 40 °C), the constructed sensor based on the catalytic activity of the Por-ZnFeO/rGO could be conveniently used for colorimetric detection of HO in the range of 0.7-30 μM with the detection limit of 0.54 μM. Moreover, the colorimetric sensor based on Por-ZnFeO/rGO exhibited a good linear response to glutathione (GHS) in the range of 2-40 μM with a low detection limit of 0.76 μM. The detection of GHS can be easily realized through the obvious color change by naked eyes without any complicated instrumentation.