A horseradish peroxidase (HRP) modified glass carbon electrode (GCE) was fabricated by using composite of multi-walled carbon nanotubes (MWCNTs), HRP and chitosan (Chi) as modifier. UV-Vis and IR spectroscopy of HRP showed that HRP retained its native structure in the composite. The Chi-HRP-
MWCNTs/GCE was applied to investigation on the direct electrochemistry of HRP in a hydrophilic ionic liquid, 1-ethyl-3-methylimidazolium tetrafluroborate ([EMIM]BF4). The cyclic voltammetric experiment results of HRP indicated that HRP exhibited a pair of well-defined and nearly symmetrical redox peaks with a formal potential of －0.247 V (vs. Ag/AgCl) in [EMIM]BF4, which resulted from the direct electron transfer between entrapped HRP and the underlying electrode. The electron transfer rate constant (ks) of HRP on the electrode surface was 3.12 s－1. HRP could maintain excellent activity in [EMIM]BF4 at 65 ℃. Further experiment demonstrated that the HRP modified electrode exhibited an electrocatalytic activity for the reduction of H2O2. The catalytic peak current was linear to H2O2 concentration in the range of 5.0×10－7 to 5.0×10－5 mol•L－1, with a detection limit of 2.0×10－7 mol•L－1. The apparent Michaelis-Menten constant (Km) was estimated to be 5.6×10－5 mol•L－1. This study can provide a new approach for developing a nonaqueous biosensor.

Key words: electrochemistry, electrocatalysis, ionic liquid, carbon nanotube, horseradish peroxidase, hydrogen peroxide