A new active layer for CO2 sensing based on semiconducting CuO-CuxFe3-xO4 (with 0 <= x <= 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO2 target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite-spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures (130-475 degrees C) and frequencies (0.5-250 kHz). The results showed a high response of 50% (R-air/R-CO2 -1.9) at 250 degrees C and 700 Hz for a CO2 concentration of 5000 ppm. (C) 2010 Elsevier B. V. All rights reserved.