Fabrication, characterization, and tests of the practical gradient microarray electronic nose with SnO(2) nanowire gas-sensing elements are reported. This novel device has demonstrated an excellent performance as a gas sensor and e-nose system capable of promptly detecting and reliably discriminating between several reducing gases in air at a ppb level of concentration. It has been found that, in addition to the temperature gradient across the nanowire layer, the density and morphological inhomogeneities of nanowire mats define the discriminating power of the electronic nose.

Electronic instruments mimicking the mammalian olfactory system are often referred to as "electronic noses" (E-noses). Thanks to recent nanotechnology breakthroughs the fabrication of mesoscopic and even nanoscopic E-noses is now feasible in the size domain where miniaturization of the microanalytical systems encounters principal limitations. Here we describe probably the simplest and yet fully functioning E-nose made of an individual single-crystal metal oxide quasi-1D nanobelt. The nanobelt was indexed with a number of electrodes in a way that each segment of the nanobelt between two electrodes defines an individual sensing elemental "receptor" of the array. The required diversity of the sensing elements is "encoded" in the nanobelt morphology via longitudinal width variations of the nanobelt realized during its growth and via functionalization of some of the segments with Pd catalyst. The proposed approach represents the combined bottom-up/top-down technologically viable route to develop robust and sensitive analytical systems scalable down to submicrometer dimensions.

Lead phthalocyanine (PbPc) single crystal whiskers were grown in vacuum via physical vapor deposition technique. The individual whiskers were used as gas-sensing elements of the conductometric gas sensing devices. These chemiresistors were found to respond sensitively and selectively to NO 2 . High crystallinity and high surface to bulk ratio determine the advantageous stability and time response characteristics of such sensing elements in comparison with polycrystalline films.

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