Carbon nanotube acoustic and optical sensors for volatile organic compound detection

Carbon nanotube coated acoustic and optical sensors have been successfully studied for volatile organic compound (VOC) sensing applications, at room temperature. Here, Langmuir–Blodgett (LB) films consisting of tangled bundles of single-walled carbon nanotubes (SWCNTs) have been transferred onto different transducing sensors by using a linker–buffer LB multilayered material of cadmium arachidate pre-deposited on the sensor surface to promote adhesion of SWCNTs. Two different kinds of sensors have been designed, fabricated and utilized: quartz crystal microbalance 10 MHz AT-cut quartz resonators and standard silica optical fibre sensors based on light reflectometry at a wavelength of 1310 nm. The proposed detection techniques are focused on two key parameters in gas sensing applications: mass and refractive index, and their changes induced by gas molecule absorption. The results indicate high sensitivity, good repeatability and reversibility. Signals from each sensor type have been analysed and processed by using pattern recognition techniques such as principal component analysis and use of artificial neural networks. The recognition of the hybrid system is successfully performed, improving the data fusion from acoustic and optical sensors with SWCNT-functionalized sensors that are highly discriminating. To our knowledge, this is the first reported study of combined hybrid integration of acoustic sensors with optical fibre sensors using nanostructured materials as single-walled carbon nanotubes for VOC detection, at room temperature.