In this work an attempt to obtain a more compact system for gas sensing, designed directly on a transducer, is presented. In the nature, a mucous layer covers the olfactory receptor cells of mammalians and selectively tunes the chemical interactions between odorous molecules and sensing systems. Such natural double layer design was reproduced in this study using a double coating comprised of a proper hydrophobic Teflon-like overlayer tuning the humidity interference between the odorous molecules and the sensitive matrix below consisting of a Zn-porphyrin film. This double coating was applied on both surfaces of the quartz crystal microbalance used for transducing into electrical signals the chemical signals deriving from the adsorption of volatile molecules. (c) 2008 Elsevier. B. V. All rights reserved.