The mixed-potential-type yttria-stabilized zirconia (YSZ)-based planar sensors using nano-structured sensing-electrodes (SE) were fabricated and evaluated in the wide range of operating temperatures under the wet (5 vol.% water vapor) condition aiming at detection of exhaust gases and ammonia slip in automobiles. The sensors using nano-structured NiO-, laminated (NiO-Au)- or pure Au-SEs fabricated by r.f. sputtering gave the sensitive and selective responses to NO2 at 600 degrees C. Furthermore, it was found that the fabrication method of Au-SE as well as the roughness of surface of YSZ solid electrolyte influenced to a large extent on the sensing characteristics of the fabricated sensors. The higher catalytic activity to electrochemical reaction of oxygen for the Au nano-particles fabricated by impregnation method resulted in the excellent sensitivity and selectivity to propene. The implementation of smooth YSZ substrates led to achieve the highly selective response to ammonia in the concentration range of 20-200 ppm. The detailed sensing characteristics and the proposed sensing mechanisms for the obtained sensors are discussed here. (C) 2008 Elsevier Ltd. All rights reserved.