In this study, we use the quartz crystal microbalance with dissipation monitoring (QCM-D) to study the immobilization of the enzyme horseradish peroxiclase (HRP) on poly(ethylene-co-acrylic acid) (PEAA) films. The surface polarity of spiri-coated PEAA films was varied by heat treatments in air or in a 30% NaOH aqueous solution leading to COOH-depleted or COOH-enriched Surfaces, respectively. Two reaction schemes, direct adsorption and amine coupling, were employed for HRP immobilization on the two surfaces. The shifts in frequency and dissipation, Delta f and Delta D, measured by QCM-D and the ratio Delta D/Delta f Were used to evaluate the binding amount and the conformation of the adsorbed enzyme. It is found that HRP immobilized via covalent linkages forms rigid and little dissipative films. In contrast, directly adsorbed HRP films exhibit a highly dissipative structure. HRP-catalyzed oxidation of the 4-chloro-1-naphthol in the presence of H2O2 was used to characterize the catalytic activity of the HRP films. The results show that the enzymatic activity of the covalently immobilized HRP tends to be higher. (c) 2005 Elsevier Inc. All rights reserved.