Semiconducting MOX sensors were initially demonstrated as thin films, although recent advances using nanoparticle morphologies have led to decreased operating temperatures and mass loadings . The MOX sensitivity to VOCs derives from the semiconductor conductivity dependence on charge carrier density. When a VOC adsorbs onto the MOX, a charge transfer produces a measurable conductivity change. The mechanism used to describe this is based on early thin film MOX VOC sensors, which described both the direct charge exchange process and a catalytically enhanced oxidation process occurring at elevated temperatures (>400 o C) . In the oxidation process, adsorbed/ionosorbed oxygen molecules withdraw electrons from the p/n-type MOX resulting in an increase/decrease of conductivity and producing different anions (O2 -, O -, O 2-) depending on the temperature. These high-energy charged species may react with VOC molecules and release the withdrawn electrons back into the MOX, undoing their previous modulation, upon exposure to a VOC molecule.