Direct electrochemistry and electrocatalysis of horseradish peroxidase immobilized in sol-gel-derived tin oxide/gelatin composite films

Horseradish peroxidase (HRP) was immobilized into a new type of sol-gel-derived nano-sized tin oxide/gelatin composite film (SnO2 composite film) using a sol-gel film/enzyme/sol-gel film “sandwich” configuration. Direct electrochemistry and electrocatalysis of HRP incorporated into the composite films were investigated. HRP/SnO2 composite film exhibited a pair of stable and quasi-reversible cyclic voltammetric peaks for the HRP Fe(III)/HRP Fe(II) redox couple with a formal potential of about −0.25 V (vs. SCE) in a pH 6.0 phosphate buffer solution. The electron transfer between the enzyme and the underlying electrode was greatly enhanced in the microenvironment with nano-SnO2 particles and nanoporous structures. Morphologies and microstructures of the composite films and HRP/composite films were characterized with TEM, AFM. Electrochemical impedance spectroscopy (EIS) was also used to feature the HRP incorporated into composite films. FTIR and UV-Vis spectroscopy demonstrated that HRP in the composite film could retain its native secondary structure. With the advantages of organic-inorganic hybrid materials, the HRP/SnO2 composite film modified electrode displayed good stability and electrocatalytic activity to the reduction of H2O2, The apparent Michaelis-Menten constant (KMapp) was estimated to be 0.345 mM, indicating a high affinity of HRP entrapped into the composite film toward H2O2.