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The vapour sensing performances of various surfactant–carbon nanotube (CNT) sensors fabricated by spray layer by layer (sLbL) towards various VOC including eleven lung cancer biomarkers have been investigated. It is found that changing the surfactants’ nature allows to efficiently tailor both the selectivity and the sensitivity of CNT vapour sensors to detect specifically some VOC biomarkers of lung cancer. An original boosting effect of chemo-resistive responses has also been evidenced and assumed to result from the combined expansion of surfactant molecules directly sheathing CNT at junctions and of those organised in micelles in the vicinity of CNT, upon analytes’ diffusion. The performances of surfactant–CNT sensors, hierarchically structured by sLbL with sodium deoxycholate (DOC), sodium dodecylbenzenesulfonate (SDBS), 1-hexadecyl trimethyl ammonium bromide (CTAB), benzalkonium chloride (BnzlkCl), and triton ® x-405 (TX405) were found to depend on the interactions of the surfactants with the analytes, on their supramolecular assembly with CNT but also on the initial resistance R 0 that can be adjusted by CNT content, surfactant:CNT ratio or the surfactant concentration over its CMC. CNT-DOC sensors were found sensitive to methanol and other alcohols but also water. TX405-CNT sensors were found sensitive to benzene, n -pentane and chloroform. SDBS-CNT sensors could detect ethanol, acetone, chloroform and water but not much biomarkers, excepted isopropanol. BnzlkCl-CNT sensors were sensitive to n -pentane, isoprene, acetone and ethanol. CTAB-CNT sensors were slightly sensitive to most VOC but did not show any strong selectivity, whereas pristine CNT sensors were found to be good to detect most aromatic VOC of the set. Moreover it is remarkable that the technique of fabrication used here is almost exclusively based on eco-friendly aqueous solutions of CNT. [ABSTRACT FROM AUTHOR]

Electrically conductive aerogels composed of carbon nanotubes (CNTs) and cellulose were used as vapour sensors for the first time. The vapour sensing behaviours of these aerogels were investigated by monitoring the electrical resistance change upon exposure to a series of volatile organic compound (VOC) vapours such as methanol, ethanol, toluene, and others. The effects of vapour types, CNT contents and vapour concentrations on relative electrical resistance change were analyzed. The results revealed that CNT–cellulose composite aerogels exhibit rapid response, high sensitivity and good reproducibility to both polar and nonpolar vapours. The dominant mechanism for these aerogels as vapour sensors is the resistance change from chemical molecule absorption by both CNT networks and cellulose matrix. This is mainly due to the unique three-dimensional (3D) porous structure of materials, which also broadens the scope of analytes to be detected. This work provides a novel concept for developing a new class of chemical sensors by combining the nature of CNTs with the 3D porous matrix. [ABSTRACT FROM AUTHOR]

Abstract: Vapour sensors based on single walled carbon nanotubes (SWCNT) networks offer a high sensitivity but poor selectivity. Different works were undertaken, with varying degrees of success, to overcome this drawback. In this context, we develop a new selective sensor architecture based on a SWCNT network covered with a mesoporous silica film elaborated by sol–gel process. The topological and chemical characteristics of this sensor are obtained by TEM, SEM, EDX, contact angle and electrical measurements. We demonstrate that highly polarised molecules are stopped by the silica layer while other molecules like NO2 can diffuse easily in the mesoporous silica layer to reach the SWCNT network without increasing the response time. [Copyright &y& Elsevier]

Abstract: Conductive biopolymer nanocomposites (CPC) have been prepared by dispersing multi-wall carbon nanotubes (CNT) “guest conducting filler” in biopolymer, poly(lactic acid) (PLA) “host matrix” via solution mixing to develop volatile organic compounds (VOC) sensors. CPC transducers were fabricated by spray layer by layer (sLbL) technique and the derived sensors chemo-resistive properties have been investigated by exposition to a set of organic vapours (chloroform, methanol, toluene and water) exhibiting different physical properties such as solubility, polarity and molecular size. The influence of both vapour nature and CNT content has been elucidated and explained on the basis of solubility parameters and percolation theory. The selectivity of PLA/CNT CPC towards vapours, was found to be well correlated to solubility parameters. Among all, chloroform was the vapour that led to the highest response of sensors. To determine the influence of crystallization on conductive network architecture and thus on chemo-resistive characteristics of PLA/CNT, a comparative study has been carried out before and after annealing of sensors. The modification induced by this thermal treatment on both surface morphology and bulk crystallinity of PLA/CNT CPC, has clearly evidenced by atomic force microscopy (AFM) and differential scanning calorimetry (DSC) are found to be responsible for important changes in vapour sensing behaviour. [Copyright &y& Elsevier]

Abstract: Inkjet-printed films of the conductive polymer polypyrrole have been used for vapour sensing at room temperature. The electrical properties, sensitivity, reproducibility and stability of the polymer chemiresistors are reported. A significant increase in conductivity was observed on the exposure of the films to the vapours of simple alcohols. The value of the fractional resistance change, ΔR/R, of the films increased linearly with increasing concentrations of both ethanol and methanol. A relatively high ΔR/R value, approximately 90%, was obtained on exposure to 5000 parts per million of methanol. The response time of the inkjet-printed sensors to polar vapours was generally shorter than that for non-polar compounds. It is suggested that the increase in conductivity may be related to a vapour-induced change in the transfer of charge carriers between the polymer chains. [Copyright &y& Elsevier]

Ion-beam sputtering deposited palladium-fluoropolymer (Pd-CFx) nano-structured composite films have been investigated as active layers for the detection of organic solvents vapours. The composites sensing properties have been studied and compared to those of homologous Au-CFx films by means of ellipsometric and quartz crystal microbalance (QCM) experiments. Differences have been shown between sensitivity, selectivity and response repeatability of Au-CFx and Pd-CFx sensors exposed to organic solvent vapours. X-ray photoelectron spectroscopy (XPS) analysis has revealed strong similarities between the two materials as to the polymer matrix structure, but higher concentration of metal oxides and fluorides in the case of palladium. The results of the analytical characterisation have been used to discuss the performance level of the sensors. [Copyright &y& Elsevier]

Chemically synthesised copper/polyaniline (PANi) nanocomposite has been utilised as a chloroform sensor for ppm level vapour concentration. The response in terms of increase in dc electric resistance on exposure to chloroform vapours has been observed. The FT–IR spectra of nanocomposite on exposure to chloroform show remarkable modifications in the far IR region indicating the interaction of chloroform with metal cluster. It is believed that the sensing mechanism mainly involves adsorption–desorption of chloroform at metal cluster surfaces. [Copyright &y& Elsevier]