Direct electrochemistry and electrocatalysis of horseradish peroxidase immobilized in graphene oxide–Nafion nanocomposite film

Direct electron transfer of horseradish peroxidase (HRP) immobilized in graphene oxide (GO)–Nafion nanocomposite film and its application as a new biosensor was investigated with electrochemical methods. Immobilized HRP shows a pair of well-defined redox waves and retains its bioelectrocatalytic activity for the reduction of H2O2 and O2. As a new sensor with excellent electrocatalytic response to the reduction of H2O2 and O2, calibrations with good linear relationships were obtained from 1.0 μmol L−1 to 1.0 mmol L−1 for H2O2 and from 0.5 μmol L−1 to 18.6 μmol L−1 for O2 with the detection limits of 4.0 × 10−7 mol L−1 for H2O2 and 1.0 × 10−7 mol L−1 for O2 at a signal-to-noise ratio of 3. Additionally, the responses showed Michaelis–Menten behavior with Kmapp values of 0.684 mmol L−1 for H2O2 and 0.0160 mmol L−1 for O2. Moreover, the cathodic peak current of an HRP/GO/Nafion/GCE biosensor decreases by less than 5% after 4 weeks. These results reveal that GO can be conveniently incorporated into a polymer nanocomposite for fabrication of new GO-based biosensors.