Direct electrochemistry and electrocatalysis of horseradish peroxidase based on clay–chitosan-gold nanoparticle nanocomposite

Gold nanoparticles stabilized by chitosan (AuCS) were hybridized with exfoliated clay nanoplates through electrostatic interaction. The resulting clay–chitosan-gold nanoparticle nanocomposite (Clay/AuCS) was used to modify glassy carbon electrode (GCE). HRP, a model peroxidase, was entrapped between the Clay/AuCS film and another clay layer. UV–vis spectrum suggested HRP retained its native conformation in the modified film. Basal plane spacing of clay obtained by X-ray diffraction (XRD) indicated that there was an intercalation–exfoliation–restacking process among HRP, AuCS and clay during the modified film drying. The immobilized HRP showed a pair of quasi-reversible redox peaks at −0.195 V (vs. saturated Ag/AgCl electrode) in 0.1 M PBS (pH 7.0), and the biosensor displayed a fast amperometric response to H2O2 with a wide linear range of 39 μM to 3.1 mM. The detection limit was 9.0 μM based on the signal to noise ratio of 3. The kinetic parameters such as α (charge transfer coefficient), ks (electron transfer rate constant) and Km (Michaelis–Menten constant) were evaluated to be 0.53, 2.95 ± 0.20 s−1 and 23.15 mM, respectively.