Direct Electrochemistry of Horseradish Peroxidase Embedded in Nano‐Fe3O4Matrix on Paraffin Impregnated Graphite Electrode and Its Electrochemical Catalysis for H2O2

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Abstract
Fe3O4particles coated with acrylic copolymer (ACP) of about 5–8 nm in diameter were synthesized and used for immobilization of horseradish peroxidase (HRP). Direct electrochemistry of HRP embedded in the nanosized Fe3O4solid matrix modified paraffin impregnated graphite electrode (PIGE) was achieved, which is related to the heme Fe(III)/Fe(II) conversion of HRP. Cyclic voltammetry gave a pair of reproducible and well‐defined redox peaks at aboutEmof‐0.295 V vs. SCE. The standard rate constantk2was determined as 2.7 s−1. It demonstrated that the nano‐Fe3O4solid matrix offers a friendly platform to assemble the HRP protein molecules and enhance the electron transfer rate between the HRP and the electrode. UV‐Vis absorption spectra and FTIR spectra studies revealed that the embedded HRP retained its native‐like structure. The HRP/Fe3O4/PIGE showed a strong catalytic activity toward H2O2. The voltammetric response was a linear function of H2O2concentration in the range of 10–140 μmol/L with detection limit of 7.3 μmol/L (s/n= 3). The apparent Michaelis‐Menten constant is calculated to be 0.42 mmol/L.

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