Direct electrochemistry and electrocatalysis of horseradish peroxidase immobilized in hyaluronic acid and single walled carbon nanotubes composite film

Direct electrochemistry and electrocatalysis of horseradish peroxidase (HRP) immobilized on a hyaluronic acid (HA)-single walled carbon nanotubes (SCNs) composite film coated glassy carbon electrode (GCE) was studied for the first time. HRP entrapped in the SCNs-HA composite film exhibited a pair of well-defined, quasi-reversible cyclic voltammetric peaks in a 0.1 M phosphate buffer solution (pH 7.0). Formal potential vs. standard calomel electrode (E°′) was −0.232 V, and E°′ was linearly dependent on the solution pH indicating that the electron transfer was proton-coupled. The current is linearly dependent on the scan rate, indicating that the direct electrochemistry of HRP in that case is a surface-controlled electrode process. UV-VIS spectrum suggested HRP retained its original conformation in the SCNs-HA film. Immobilized HRP showed excellent electrocatalysis in the reduction of hydrogen peroxide (H₂O₂).