Carbon nanotubes-based surface acoustic waves oscillating sensor for vapour detection

Surface acoustic waves (SAWs) sensors coated by either single-wall carbon nanotubes (SWCNTs) or multi-wall carbon nanotubes (MWCNTs) have been designed and developed for chemical detection of volatile organic compounds (VOCs), at room temperature. Upon individual exposure to 86 ppm ethanol, 178 ppm ethylacetate and 93 ppm toluene in nitrogen, the resonance frequency of the SAW 433.92 MHz oscillating sensor, based on ST-cut,X-propagation quartz substrate coated by a 0.1-μm-thick SiO2 guiding layer, exhibits high downshift of 720 (150), 670 (160), 450 (110) kHz, respectively, for SWCNTs (MWCNTs) sensing films dispersed into solvent of ethanol. Higher sensitivity up to 3-4 orders of magnitude than that of existing organic layer-coated SAW sensors can be achieved, at room temperature. The selectivity to VOCs under test can be controlled by the type of organic solvent used to disperse the carbon nanotubes as sensing materials onto SAW sensors. The analyte/coating interactions and the sensing mechanisms between molecular species to be detected and the carbon nanotubes are preliminarily investigated.