All villi-like metal oxide nanostructures-based chemiresistive electronic nose for an exhaled breath analyzer

Chemiresistive electronic nose (CEN) composed of villi-like nanostructures (VLNs) of SnO2 and WO3, and Au-functionalized VLNs was fabricated by applying electron-beam evaporation in a glancing angle deposition mode. The VLNs-based CEN with a back-heater (212 °C) shows high responses with low detection limits of parts per billion (ppb)-levels for NO and NH3 vapors at 80% relative humidity atmosphere. The enhanced sensitivities in a high humidity condition turn out to be attributed to the spillover effect by the Au nanoparticles and a large surface-to-volume ratio in porous VLNs. Employing Au NPs on VLNs leads to the increase of O− ions via the spillover effect which impedes the adsorption of water molecules, maintaining the enhanced responses against environmental humidity. Consequently, high responses for NO and NH3 vapors maintain even in the high humidity condition. Herein, with the principal component analysis (PCA), we demonstrate highly selective detection of NO and NH3 vapors against C2H5OH, CO, C7H8, C6H6, and CH3COCH3 vapors. These results open up wide applications of the VLNs-based CEN as an inexpensive and non-invasive diagnostic tool for asthma and kidney disorder.