Microchim Acta 152, 277–283 (2006) DOI 10.1007/s00604-005-0447-z Original Paper Glucose Biosensor Based on the Use of a Carbon Nanotube Paste Electrode Modified with Metallic Particles Guillermina L. Luque, Nancy F. Ferreyra, and Gustavo A. Rivas  INFIQC, Physical Chemistry Department, C ordoba National University, 5000 C ordoba, Argentina Published online December 16, 2005 # Springer-Verlag 2005 Abstract. This work reports on the performance of new glucose biosensors based on the combination of the electrocatalytic properties of metals and carbon nanotubes towards the reduction of hydrogen peroxide with the biocatalytic activity of glucose oxidase (GOx). The bioelectrodes were obtained by dispersing the metal particles, enzyme and multi-wall carbon nano- tubes within a mineral oil binder. The strong electro- catalytic activity of copper and iridium towards the reduction of hydrogen peroxide has made possible an important improvement in the sensitivity for the deter- mination of glucose compared to the carbon nanotube composite without metals. A highly sensitive and selective amperometric detection of glucose becomes possible at very low potentials (0.100 V). The pres- ence of the protein enables a better dispersion of the metals within the composite matrix, thus allowing an additional enhancement in the response to hydrogen peroxide. The influence of the amount of copper in the composite on the analytical performance of the bioelectrode is discussed. A biosensor containing 0.77% w=w Cu and 10.0% w=w GOx gave a fast response (10.0 s), a linear relationship between current and glucose concentration up to 1.20  10 2 M, and a detection limit of 2.0  10 5 M. A similar behavior was found for a carbon nanotube-composite electrode containing iridium. Key words: Carbon nanotubes; composite; glucose biosensor; glucose oxidase; copper; iridium; hydrogen peroxide. Carbon nanotubes (CNTs), discovered in 1991 [1], are a new type of carbon material obtained by folding graphene layers into carbon cylinders. They present a closed topology and tubular structure and possess diameters of several nanometers and lengths of many microns [2, 3]. Basically, there are two types of carbon nanotubes, multi-wall carbon nanotubes (MWCNTs) and single-wall carbon nanotubes (SWCNTs) [2]. They can behave as metals or semiconductors depending on their structure, mainly on their diameter and helicity [2–4]. Carbon nanotubes have received enormous atten- tion for the preparation of electrochemical sensors due to their unique properties, as it was reviewed by Zhao et al. [5], Wang [6] and Gooding [7]. Several strategies have been proposed for the immobilization of carbon nanotubes on electrochemical transducers. Wang et al. reported a marked decrease in the over- voltage for the oxidation of NADH using composites obtained by dispersing CNTs in a Teflon binder [8, 9]. Other interesting protocol for immobilizing CNTs have been reported by Li et al. [10] who proposed the electrocatalytic oxidation of norepinephrine at a GCE modified with SWCNTs. Compton et al. [11]  Author for correspondence. E-mail: grivas@mail.fcq.unc. edu.ar