Wood identification by a portable low-cost polymer-based electronic nose

The rapid and reliable identification of woods is a difficult task, yet extremely necessary for the control of illegal logging or trade of protected species. In this paper we describe a portable low-cost electronic nose based on conductive polymers, capable of distinguishing pairs of similar-looking woods, aiming to help wood traders to comply with the determinations of the United Nations (UN) Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Examples of woods with CITES restrictions are (i) mahogany (Swietenia macrophylla) and Spanish-cedar (Cedrela fissilis), and (ii) Brazilian walnut (Ocotea porosa) and black-cinnamon (Ocotea catharinensis). The e-nose consists of an array of four different gas sensors fabricated by the deposition of thin doped conductive polymer films onto the surface of interdigitated metallic electrodes. The electrical conductance responses of the sensors upon exposure to the volatile compounds emitted by the wood specimens, after scratching their surface, were evaluated by principal component analysis (PCA). The data can be processed on small computers or even on smart phones. The analysis time is only 10-15 min. Leave-one-out analysis gave a classification hit rate of 100% for group (i) and 94% for group (ii). Hence, this is an extremely viable method for standard control use in remote places such as roads in the Amazon forest, which are sometimes hundreds of miles away from urban centers, where conventional analyses could be performed.