Sensing properties of buffered and not buffered carbon nanotubes by fibre optic and acoustic sensors.

Single-walled C nanotubes (SWCNTs) are advanced nanostructured materials with promising sensing properties in terms of sensitivity, low sub-ppm limit of detection, online and real-time vapor detection, at room temp. This work is focused on the study of the sensitivity to arom. volatile org. compds. (VOCs) of std. SiO2 optical fiber (SOF) and quartz crystal microbalance (QCM) sensors incorporating Langmuir-Blodgett multilayers of SWCNTs. Multilayers of SWCNTs with different thicknesses and successfully transferred directly onto the sensors' surface were tested for the detection of toluene and xylene at room temp. and compared with the sensing performances of SWCNT multilayers buffered by a linker multilayer of Cd arachidate. The optical and acoustic sensors' principle of operation relies resp. on the complex dielec. function and mass change induced by target analyte mols. adsorbed into the sensitive nanomaterials. A time division multiplexing approach for both optical and acoustic chem. sensors was exploited to simultaneously test „T8 SOF and 6 QCM sensors. The results obtained demonstrate that the sensors based on SWCNTs provide high sensitivity, very low limits of VOC detection and fast response, at room temp., with a clear dependence of the sensors' sensitivities on the nanomaterial thickness. Furthermore, higher sensitivity was obsd. in the case of optical fiber sensors exposed to xylene; in addn., behavior with the opposite sign in the optical response occurred between buffered and not buffered SWCNTs overlayers. Also, effects of humidity were investigated in the case of optical fiber sensors demonstrating a linear dependence of the response at a const. temp. of 28„a.