In this work, we report on the application of multi-walled carbon nanotubes as gas sensors. We use the vertical growth of aligned carbon nanotubes on structure surfaces composed by a set of Ni electrodes and SiO2 surfaces fraction. The results show that carbon nanotubes could be efficient in terms of sensibility for detection of pollutant species like NH3 even at ambient temperature. The determination of the adsorption energies for various species on the basis of a semi-empirical potential approach show that gases, particularly the polar one, are able to bind strongly on carbon nanotubes surfaces and could explain at least qualitatively the experimental results. (c) 2006 Elsevier B.V. All rights reserved.