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Mimicking the biological olfactory receptor array that possesses large surface area for molecule capture, vertically aligned ZnO nanowire arrays, used as structural templates, were coated with SnO2/noble metal nanoparticles as active materials for fabrication of 3-D gas sensors. The gas sensors showed room-temperature responses to environmental toxic gases, such as NO2 and H2S, down to ppb level, which can be attributed to the large surface area of their 3D structure and catalytic behaviors of noble metals. A sensor array composed of three sensors with the different noble metals decoration (Pd, Pt, and Au) has shown capability to discriminate five different gases (H2S, NO2, NH3, H2, and CO) when using principal component analysis (PCA) incorporated the response speed as a discrimination factor. This study demonstrates a rational strategy to prepare sensing devices with 3-D structures for selective detection, which can be readily extended to other sensing materials that can be hardly grown as 3-D nanowire arrays.