Direct Electrochemistry of Horseradish Peroxidase Embedded in Nano‐Fe 3 O 4 Matrix on Paraffin Impregnated Graphite Electrode and Its Electrochemical Catalysis for H 2 O 2

Fe 3 O 4 particles 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 Fe 3 O 4 solid 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 about E m of‐0.295 V vs. SCE. The standard rate constant k 2 was determined as 2.7 s −1 . It demonstrated that the nano‐Fe 3 O 4 solid 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/Fe 3 O 4 /PIGE showed a strong catalytic activity toward H 2 O 2 . The voltammetric response was a linear function of H 2 O 2 concentration 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.