Carbon nanotubes thin films fiber optic and acoustic VOCs sensors: Performances analysis

This work is focused on the performances analysis of silica optical fiber (SOF) and quartz crystal microbalance QCM) volatile organic compounds (VOCs) sensors, coated by single-walled carbon nanotubes (SWCNTs) multilayers, towards toluene and xylene vapors, at room temperature. The Langmuir-Blodgett (LB) technique has been used for the deposition of carbon nanotubes directly onto the optical and acoustic sensors substrates. A time division multiplexing approach has been used in order to simultaneously test up to eight SOF and six QCM chemical sensors in the same test chamber. The results obtained demonstrate good sensitivity, fast response and high repeatability provided by the proposed sensors even at very low concentrations. Resolutions in the ppm and sub-ppm range have been found towards the tested VOCs, for both optical and acoustic transducers. The effects of the SWCNTs film thickness and even of a cadmium arachidate (CdA) buffer multilayer, exploited in the past to improve the adhesion of nanotubes onto the sensors substrates, on the performances of SOF and QCM transducers have been investigated. To the aim, several optical and acoustic sensors with a different number of SWCNTs LB layers, directly deposited onto optical fibers and quartz surfaces and buffered by a CdA linker material, have been fabricated and simultaneously exposed, at room temperature, to different concentration pulses of toluene and xylene. The results obtained demonstrate the possibility to use the data coming from carbon nanotubes SOF and QCM sensors to improve the VOC discrimination by means of the hybrid system based on these two complementary transducers by pattern recognition methods. (c) 2006 Elsevier B.V. All rights reserved.