In this work, we report a remarkably improved toluene response and superior cross-sensitivity against H-2 S molecules by combining Pd catalysts and highly porous WO3 nanofibers (NFs). We functionalized Pd catalysts inside and/or outside of WO3 NFs synthesized by electrospinning, which is a facile and versatile process for producing webs of metal oxide NFs. Pd-embedded WO3 NFs were obtained by the electrospinning of a Pd and W composite precursor/poly(methyl methacrylate) (PMMA) solution followed by calcination at 700 degrees C. Pd nanoparticles (NPs)( 6-10 nm) synthesized by a polyol method were decorated on the WO3 NFs (Pd-NPs/WO3 NFs) by the attachment of the Pd NPs on as-prepared WO3 NFs. The gas sensing characteristics of pure WO3, Pd-embedded WO3, Pd-NP5/WO3, and Pd-NPs/Pd-embedded WO3 NFs were tested using H2S and toluene gases in a highly humid atmosphere (RH 90%), which is similar to human exhaled breath. The results showed that the Pd-NPs/Pd-embedded WO3 NFs whose inner and outer layers were decorated by Pd catalysts, exhibited a high toluene response (R-air/R-gas= 5.5 at 1 ppm) and remarkable selectivity against H-2 S (R-air/R-gas = 1.36 at 1 ppm) at 350 C degrees, whereas pristine WO3 NFs showed superior H2 S response (R-air/R-gas =11.1 at 1 ppm) along with a negligible response toward toluene (R-air/R-gas =1.27 atl ppm). The highly porous WO3 NFs decorated with Pd catalysts, exhibited potential feasibility, i.e., a low limit of detection (LOD) of 20 ppb (R-air/R-gas = 1.32) at 350 degrees C, for application in VOCs sensors, particularly for diagnoses of lung cancer. (C) 2013 Elsevier B.V. All rights reserved.