The direct voltammetry and electrocatalytic properties of catalase, which was adsorbed on the surface of multiwall carbon nanotubes (MWCNTs), was investigated. A pair of well-deWned and nearly reversible cyclic voltammetry peaks for Fe(III)/Fe(II) redox couple of catalase adsorbed on the surface of MWCNTs at approximately ¡0.05 V versus reference electrode in pH 6.5 buVer solution, indicating the direct electron transfer between catalase and electrode. The surface coverage of catalase immobilized on MWCNTs glassy carbon electrode was approximately 2.4£10¡10 mol cm¡2. The transfer coeYcient () was calculated to be 0.4, and the heterogeneous electron transfer rate constant was 80 s¡1 in pH 7, indicating great facilitation of the electron transfer between catalase and MWCNTs adsorbed on the electrode surface. The formal potential of catalase Fe(III)/Fe(II) couple in MWCNTs Wlm had a linear relationship with pH values between 2 and 11 with a slope of 58mV/pH, showing that the electron transfer is accompanied by single proton transportation. Catalase adsorbed on MWCNTs exhibits a remarkable electrocatalytic activity toward the reduction of oxygen and hydrogen peroxide. The value for calculated Michaelis–Menten constant (1.70mM) was high, indicating the potential applicability of the Wlms as a new type of reagentless biosensor based on the direct electrochemistry of the catalase enzyme. 2005 Elsevier Inc. All rights reserved.
