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Abstract In the present work, nanostructures of zeolitic imidazolate frameworks (ZIF-8 and ZIF-67) were combined to obtain a novel chemoresistive sensor, improving the response of ZIF-67 and facilitating measurement of ZIF-8 by decreasing the resistivity. The sensor detected concentrations as low as 10 ppm of toluene, ethanol, carbon monoxide, hydrogen and nitrogen dioxide, showing large resistance change. In the case of toluene and hydrogen for a 10 ppm concentration, the response of ZIFs combination based sensor was significantly higher than ZIF-67 based sensor; about 7.0 and 5.4 times, respectively. [ABSTRACT FROM AUTHOR]

In this paper, propagation of shear horizontal surface acoustic waves (SH-SAW) in nanoparticle layers was studied by means of dispersion acoustic theory in waveguides. These studies have allowed to obtainment of properties of nanoparticles layers, such as shear stiffness modulus. In addition, the numerical analysis of multi-guiding layers have allowed for the design of an innovative, simple and inexpensive gas sensor based on elastic properties variation of the nanoparticles layers due to their interaction with gases. Each sensor has been prepared by coating a uniform layer of nanostructured indium tin oxide (ITO) nanoparticle layer on a piezoelectric material (quartz), working as a guiding layer by confining SH-SAW energy and obtaining a Love-wave sensor. The perturbation produced in the elastic properties of the nanoparticle layer due to its interaction with gases induced a change in wave velocity that was detected by the frequency shift of an oscillator, working as a sensitive layer. Therefore, the Love-wave sensor was optimized with multi-guiding layers containing an intermediate guiding layer of SiO 2 . The Love-wave multi-guiding layer sensor was tested to different concentrations of toluene and benzene, measurements showed high sensitivity, short response time, and good reproducibility, and ability to detect very low concentrations of test gases, such 1 ppm of toluene and 25 ppm of benzene. [ABSTRACT FROM AUTHOR]

An array comprised of four magnonic gas sensors based on magnetic nanoparticles layers of CuFe 2 O 4 , MnFe 2 O 4 , ZnFe 2 O 4 and CoFe 2 O 4 was developed and tested with dymethylformamide, isopropanol, xylene and toluene. Magnonic gas sensors were composed of an yttrium iron garnet (YIG) epitaxial thin film as a magnetostatic spin waveguide combined with a spin-coated layer of magnetic nanoparticles as a sensitive layer. The magnetostatic spin waves (MSW) were very sensitive to perturbations produced in the magnetic properties of the nanoparticle layers due to interaction with gases, allowing the detection of low concentrations of gases. Finally, the sensitive layers of the magnetic nanoparticles revealed a differentiated response in regard to the gases used to test the array. Therefore, the gases could be discriminated and classified using pattern recognition techniques, such as principal component analysis and artificial neural networks. [ABSTRACT FROM AUTHOR]

A highly sensitive, simple and inexpensive Love-wave gas sensor based on surface functionalized nanoparticles has been developed. A thin film of amine-terminated iron oxide nanoparticles was successfully deposited onto the surface of Love-wave sensor to serve as a gas-sensing layer. A gas sensing test was carried out with N,N-dimetilformamide (DMF), which revealed that the Love wave sensor with surface functionalized nanoparticles has a wide concentration range with very high response, fast response–recovery time and stable repeatability. [ABSTRACT FROM AUTHOR]

A novel array comprised of six Love-wave sensors based on metal oxide nanoparticles layers (ZnO and TiO 2 ) mixed with different metals (Co and Pt) was developed to detect, discriminate and classify toxic gases. The metal oxide nanoparticles worked as guiding and sensitive layers at the same time for every sensor. The properties of the different layers of nanoparticles change due to that interaction with the gases, and consequently each sensor suffers a different frequency shift. The array has been tested with different concentrations of ammonia, toluene and xylene. Very low concentrations of these samples have been detected and discriminated by principal component analysis, such as 10 ppm of ammonia, 5 ppm of toluene and 10 ppm of xylene. A correct classification of the measurements has been carried out by means of probabilistic neural network. [ABSTRACT FROM AUTHOR]

This paper presents a robust, simple and highly sensitive method to detect vapour compounds using a magnetostatic spin wave (MSW) tunable oscillator based on a yttrium iron garnet (YIG) epitaxial thin film coupled to a coplanar waveguide resonator. In this work, the device has been tested as relative humidity sensor. For this purpose, the coplanar waveguide resonator was coated with polyvinylpyrrolidone (PVP) polymer and used as a humidity probe. A dielectric change in the PVP due to a change in the ambient humidity introduces a fast phase shift in the probe, which causes a frequency shift in the MSW oscillator. The humidity sensing behavior of this device was investigated at room temperature over a range of 12.5–95% relative humidity (RH). Furthermore, the device was used to monitor human breath as a non-invasive sensor, showing great adaptability and ease of use in a real application. In conclusion, the sensor exhibited reproducibility, accuracy, high sensitivity, and fast response and recovery times. It also has the advantage of being simple and cost-effective. [ABSTRACT FROM AUTHOR]

Abstract: The electrospinning technique has allowed that very different materials are deposited as sensitive layers on Love-wave devices forming a low cost and successful sensor array. Their excellent sensitivity, good linearity and short response time are reported in this paper. Several materials have been used to produce the nanofibers: polymers as Polyvinyl alcohol (PVA), Polyvinylpyrrolidone (PVP) and Polystirene (PS); composites with polymers as PVA+SnCl4; combined polymers as PS+Poly(styrene-alt-maleic anhydride) (PS+PSMA) and metal oxides (SnO2). In order to test the array, well-known chemical warfare agent simulants (CWAs) have been chosen among the volatile organic compounds due to their importance in the security field. Very low concentrations of these compounds have been detected by the array, such as 0.2ppm of DMMP, a simulant of sarin nerve gas, and 1ppm of DPGME, a simulant of nitrogen mustard. Additionally, the CWA simulants used in the experiment have been discriminated and classified using pattern recognition techniques, such as principal component analysis and artificial neural networks. [Copyright &y& Elsevier]

The goal of this work has been to study the polyvinylpyrrolidone (PVP) fibers deposited by means of the electrospinning technique for using as sensitive layer in surface acoustic wave (SAW) sensors to detect volatile organic compounds (VOCs). The electrospinning process of the fibers has been monitored and RF characterized in real time, and it has been shown that the diameters of the fibers depend mainly on two variables: the applied voltage and the distance between the needle and the collector, since all the electrospun fibers have been characterized by a scanning electron microscopy (SEM). Real-time measurement during the fiber coating process has shown that the depth of penetration of mechanical perturbation in the fiber layer has a limit. It has been demonstrated that once this saturation has been reached, the increase of the thickness of the fibers coating does not improve the sensitivity of the sensor. Finally, the parameters used to deposit the electrospun fibers of smaller diameters have been used to deposit fibers on a SAW device to obtain a sensor to measure different concentrations of toluene at room temperature. The present sensor exhibited excellent sensitivity, good linearity and repeatability, and high and fast response to toluene at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: An array of Love-wave sensors based on quartz and Novolac has been developed to detect chemical warfare agents (CWAs). These weapons are a risk for human health due to their efficiency and high lethality; therefore an early and clear detection is of enormous importance for the people safety. Love-wave devices realized on quartz as piezoelectric substrate and Novolac as guiding layer have been used to make up an array of six sensors, which have been coated with specific polymers by spin coating. The CWAs are very dangerous and for safety reasons their well known simulants have been used: dimethylmethyl phosphonate (DMMP), dipropyleneglycol methyl ether (DPGME), dimethylmethyl acetamide (DMA), dichloroethane (DCE), dichloromethane (DCM) and dichloropentane (DCP). The array has been exposed to these CWA simulants detecting very low concentrations, such as 25ppb of DMMP, a simulant of nerve agent sarin. Finally, principal component analysis (PCA) as data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as patterns classification technique have been applied. The performance of the sensor array has shown stability, accuracy, high sensitivity and good selectivity to these simulants. [ABSTRACT FROM AUTHOR]

Abstract: In this work we report on the fabrication and characterization of single-walled carbon nanotubes (SWCNTs) as sensitive layers for the detection of simulants of Chemical Warfare Agents (CWAs). The microsensor fabrication has been achieved after the wafer scale integration of the selective synthesis of SWCNTs as sensitive layer. Their electrical characterization has been carried out by measuring the resistance changes of the SWCNT networks when interacting with very low concentrations of CWA simulants such as dimethyl methyl phosphonate (DMMP), dipropylene glycol methyl ether (DPGME) and dimethylacetamide (DMA) at low temperatures, which are simulants of Sarin, Nitrogen Mustard and Distilled Mustard, respectively. [Copyright &y& Elsevier]