Direct electrochemistry of horseradish peroxidase in gelatin-hydrophobic ionic liquid gel films

The direct electrochemistry and electrocatalysis of horseradish peroxidase (HRP) immobilized on a gelatin – N, N-dimethylformamide (DMF) – hydrophobic ionic liquid (i.e. 1-octyl-3-methylimidazolium hexafluorophsohate) gel film coated glassy carbon electrode has been studied for the first time. The immobilized HRP exhibits a pair of well-defined quasi-reversible peaks in pH 7.0 phosphate buffer solutions, which results from the direct electron transfer between the enzyme and the underlying electrode. In this case there is about 2.7% of the immobilized HRP undergoing the electrochemical reaction, which corresponds to multi-layer of HRP on the electrode surface. The HRP immobilized has higher thermal stability than in gelatin hydrogel. Experiment results also show that the voltammetric behavior of the enzyme electrode depends on the type of room temperature ionic liquid (RTIL) used. When a more hydrophobic RTIL is adopted, the resulting enzyme electrode gives better performance. In the presence of hydrogen peroxide, the enzyme electrode shows sensitive response. The sensitivity of the catalytic peak is up to 1.38 A cm−2 M−1 and the Michaelis constant is down to 6.84 × 10−5 M, which are superior to that reported elsewhere. In addition, the UV–visible spectra of HRP entrapped in different films and the mass transfer of hydrogen peroxide are discussed as well.