Nanocomposite-based quantum resistive vapour sensors (vQRS) have been developed from the assembly of hybrid copolymers of polyhedral oligomeric silsesquioxane (POSS) and poly(methyl methacrylate) (PMMA) or poly(styrene) (PS) with carbon nanotubes (CNT). The originality of the resulting conducting architecture is expected to be responsible for the ability of the transducer to detect sub-ppm concentrations of ammonia and formaldehyde at room temperature despite the presence of humidity. In particular, the boosting effect of POSS is evidenced in CNT-based nanocomposite vQRS. The additive fabrication by spraying layer-by-layer provides (sLbL) is an effective method to control the reproducibility of the transducers’ chemo-resistive responses. In dry atmosphere, the two types of sensors showed a high sensitivity towards both hazardous gases, as they were able to detect 300 ppb of formaldehyde and 500 ppb of ammonia with a sufficiently good signal to noise ratio (SNR > 10). They also exhibited a quick response times less than 5 s for both vapours and, even in the presence of 100 ppm of water, they were able to detect small amounts of gases (1.5 ppm of NH₃ and 9 ppm of CH₂O). The results suggest promising applications of POSS-based vQRS for air quality or volatolome monitoring. Full article

Different grades of chemically functionalized carbon nanotubes (CNT) have been processed by spraying layer-by-layer (sLbL) to obtain an array of chemoresistive transducers for volatile organic compound (VOC) detection. The sLbL process led to random networks of CNT less conductive, but more sensitive to vapors than filtration under vacuum (bucky papers). Shorter CNT were also found to be more sensitive due to the less entangled and more easily disconnectable conducting networks they are making. Chemical functionalization of the CNT’ surface is changing their selectivity towards VOC, which makes it possible to easily discriminate methanol, chloroform and tetrahydrofuran (THF) from toluene vapors after the assembly of CNT transducers into an array to make an e-nose. Interestingly, the amplitude of the CNT transducers’ responses can be enhanced by a factor of five (methanol) to 100 (chloroform) by dispersing them into a polymer matrix, such as poly(styrene) (PS), poly(carbonate) (PC) or poly(methyl methacrylate) (PMMA). COOH functionalization of CNT was found to penalize their dispersion in polymers and to decrease the sensors’ sensitivity. The resulting conductive polymer nanocomposites (CPCs) not only allow for a more easy tuning of the sensors’ selectivity by changing the chemical nature of the matrix, but they also allow them to adjust their sensitivity by changing the average gap between CNT (acting on quantum tunneling in the CNT network). Quantum resistive sensors (QRSs) appear promising for environmental monitoring and anticipated disease diagnostics that are both based on VOC analysis. Full article