Investigations are reported regarding the electrochemical performance of catalase (CAT) immobilized on a film composed of chitosan-wrapped single-walled carbon nanotubes (SWNTs), and the use of such a system as a biosensor. The immobilized CAT displays a pair of well-defined and quasi-reversible redox peaks, with a formal potential (E(01)) of -0.476 V vs. SCE in 0.1 M, pH 7.0 phosphate buffer solution: also the electrochemical response indicates a surface-controlled electrode process. The dependence of formal potential on solution pH indicated that the direct electron transfer reaction of CAT is a one-electron transfer coupled with a one-proton transfer reaction. The heterogeneous electron transfer rate constant was measured as 118 s(-1), indicating electron transfer between catalase and the modified electrode surface is greatly improved over that which is typically reported in the literature. This result is likely attributed to close contacts between the electroactive centers and the SWNTs. Experimental results demonstrate that absorbed CAT exhibits remarkable electrocatalytic activities toward the reduction of oxygen, hydrogen peroxide and nitrite. Also, the modified electrode exhibited good analytical performance for the amperometric determination of hydrogen peroxide and nitrite, and might find use as a third-generation biosensor based on the direct electrochemistry of catalase. (c) 2008 Elsevier B.V. All rights reserved.