Highly selective ppb-level detection of NH₃ and NO₂ gas using patterned porous channels of ITO nanoparticles

We demonstrate the formation of micro-patterned porous electronic channels of tin-doped indium oxide nanoparticles (ITO NPs) and their utilization as sensor transducers for the detection of NH₃ and NO₂ gas in air. The ITO NP channels were formed by dipping a molecularly patterned solid substrate into an ITO NP suspension and then pulling it vertically at a precisely controlled speed. The ITO NPs were self-assembled on the intended regions with high definition, as the NPs were selectively adsorbed on the polar SiO₂ regions avoiding the nonpolar regions. The thickness of the assembled ITO NP patterns could be modulated by controlling the pulling speed. The NPs formed a dense percolated network through which current could flow without any post-treatment such as heat annealing. By forming electrodes on the assembled ITO NP patterns, we fabricated sensor transducers for the detection of ammonia and nitrogen dioxide. The sensor showed a highly sensitive detection of NH₃ and NO₂ gas down to ppb-level. Furthermore, the sensor response changed in opposite direction to reducing NH₃ and oxidizing NO₂ gases, which shows that our sensor can be utilized in the selective detection of NH₃ and NO₂.