Metal oxide semiconductors (MOS) are important candidates as the sensing layer for chemical gas sensors to detect volatile organic compounds (VOCs). However, the low surface activity limits the use of MOS in future high performance gas sensors. The design of susceptive nanostructures with prominent surface modification can be an effective strategy to achieve high sensitivity and high selectivity. Herein, Pt nanoparticles with a fine size of below 1 nm serving as the sensitizers are functionalized on porous W18O49 nanospheres via atomic layer deposition and investigated for acetone detection. The W18O49/Pt spheres combine the advantages of fast gas diffusion enabled by the porous shells and catalytic properties of Pt nanocatalysts. Gas sensing tests reveal that W18O49/Pt has a very high response to 20 ppm acetone (Ra/Rg = 85), which is ∼40 times higher than that of pure W18O49 (Ra/Rg = 2.1) at a low operating temperature of 180 °C. Meanwhile, W18O49/Pt shows fast response-recovery speed and good stability as well as excellent selectivity to acetone against other interfering gases. In addition, an ultrahigh sensitivity of 1.01 ppm−1 and a very low limit of detection of 52 ppb is obtained. The superior gas sensing performances of the W18O49/Pt materials indicates a strong potential for detection of biomarkers for exhaled breath diagnosis, and also paves the way to manipulate other metal oxide semiconductor-based sensors with high performances. © 2019 Elsevier B.V.