On Sensing Nitro-Group Containing Compounds Using Thin Planar Arrays of Titanium Dioxide Nanowires

Previous laboratory results have suggested that unheated TiO
₂
nanowire arrays provide a means to detect trace level concentrations of nitro-group containing compounds in the gas phase with fast response and high chemical selectivity. The detection method is based on the chemiresistive effect, where an electron-deficient compound adsorbed to the surface of an n-type semiconductor causes a surface charge deficit on the semiconductor leading to an increase in its resistance. However, a major issue with this method is that chemiresistive sensors based on TiO
₂
are also sensitive to the presence of water vapor, and this cross-sensitivity could lead to artifacts for sensors used under environmental conditions. Results are presented here, where thin planar arrays of TiO
₂
nanowires were tested to determine the sensitivity towards water vapor, along with the detection limits and response times towards several nitrocontaining organic molecules as a function of gas-phase water vapor concentration. When water vapor concentrations were carefully controlled to ensure they remain constant throughout the testing cycle, it was found that TiO
₂
nanowire devices could detect 2,4,6-trinitrotoluene at a concentration as low as a few tens of part per trillion by volume with a response time in the range of 10
²
-10
³
s, depending on experimental conditions.