Peroxidase mimetic activity of porphyrin modified ZnFe2O4/reduced graphene oxide and its application for colorimetric detection of H2O2 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 ZnFe2O4 nanoparticles loaded on the surface of reduced graphene oxide (Por-ZnFe2O4/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 ZnFe2O4 nanoparticles, ZnFe2O4/rGO and Por-ZnFe2O4, Por-ZnFe2O4/rGO was proved to possess the highest peroxidase-like activity. Electron spin resonance (ESR) verified the catalytic activity of Por-ZnFe2O4/rGO for H2O2 was due to hydroxyl radical from decomposition of H2O2. Temperature and pH strongly affected the peroxidase-like activity of Por-ZnFe2O4/rGO nanocomposites. Under optimal conditions (pH = 4, 40 degrees C), the constructed sensor based on the catalytic activity of the Por-ZnFe2O4/rGO could be conveniently used for colorimetric detection of H2O2 in the range of 0.7-30 mu M with the detection limit of 0.54 mu M. Moreover, the colorimetric sensor based on Por-ZnFe2O4/rGO exhibited a good linear response to glutathione (GHS) in the range of 2-40 mu M with a low detection limit of 0.76 mu M. The detection of GHS can be easily realized through the obvious color change by naked eyes without any complicated instrumentation.