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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: A Love-wave device and a PDMS microfluidic chip have been developed in order to measure immunoreactions in liquid media, operating in dynamic mode (continuous flow-through). The obtained results with the above system for the detection of rabbit immunoglobulin by means of an antibody of goat anti-rabbit have been compared with those obtained by the most used acoustic wave device, the quartz crystal microbalance (QCM), which has worked in static mode. It has been demonstrated once again that QCM is an excellent tool as an immunosensor, although the Love-wave device is a good alternative due to its higher sensitivity. The dynamic mode improves the response time and the limit of detection. In addition, the use of microchannels has allowed working with a small sample volume for a long period of time in dynamic mode. On the other hand, a secondary antibody conjugated with gold nanoparticles has been used as a different method to measure the desired concentrations of antigens, obtaining in this case, a greater frequency shift. [Copyright &y& Elsevier]

An immunosensor based on a Love-wave device and a PDMS microfluidic chip has been developed to detect potentially pathogenic microorganisms in real time. In order to characterize and test the immunosensor, the M13 bacteriophage has been chosen as a model of microorganism. The M13 was detected with the mouse monoclonal antibody, anti-M13 (AM13), which has been immobilized on the Love wave-device. The immunoassay has been carried out in a dynamic mode (continuous flow) through microchannels with the goal of obtaining a short response time in detecting a small volume of a sample of M13 bacteriophage. The concentrations of the bacteriophage have been varied between 5×108 pfuml−1 and 2×1010 pfuml−1, a range for which a fast detection and a favorable discrimination among concentrations have been achieved. The AM13 has been also used as a secondary antibody in order to measure lower concentrations such as 5×107 pfuml−1. The Double-Layer Agar technique has been used to quantify, as plaques-forming unit (pfu), the number of M13 bacteriophage in the initial sample as well as those linked to the sensor surface during the detection. Finally, the number of bacteriophage was estimated by calculating the mass sensitivity. The values obtained in both procedures have been very similar. [ABSTRACT FROM AUTHOR]

Abstract: The goal has been to develop a Love-wave device and a PDMS microfluidic chip in order to measure immunoreactions in liquid media, operating in dynamic mode (continuous flow-through). The obtained results have been compared with the most used acoustic wave device, the quartz crystal microbalance (QCM), which worked in static mode. It has been demonstrated once again that QCM is an excellent tool as immunosensor, although Lovewave device is a good alternative due to its high sensitivity. Besides, the response time and limit of detection are improved working in dynamic mode. On the other hand, a secondary antibody conjugated with gold nanoparticles has been used as a method to measure concentrations of antigens obtaining a great frequency shift. [Copyright &y& Elsevier]

Abstract: An array made up of Love wave sensors based on quartz/SiO2 is proposed as a detection system for chemical warfare agents (CWA). The array is composed of one reference and six devices coated with different polymers means of spray coating technique. The system has been tested with well-known CWA simulants: dimethylmethyl phosphonate (DMMP), dipropyleneglycol methyl ether (DPGME), dimethylmethyl acetamide (DMA), dichloroethane (DCE), dichloromethane (DCM), and dichloropentane (DCP), detecting very low concentrations, such as 40ppb of DMMP, a simulant of sarin nerve gas. Additionally, principal component analysis (PCA) as a data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as a pattern classification technique, have been applied, obtaining a clear discrimination and a correct classification. [Copyright &y& Elsevier]

Abstract: An array made up of Love-wave sensors has been developed as a detection system for chemical warfare agents (CWAs). This array has been tested with well-known CWA simulants detecting very low concentrations, such as 40 ppb of DMMP, a simulant of sarin nerve gas, 250 ppb of DPGME, a simulant of nitrogen mustard and 15ppm of DMA, a simulant of distilled mustard. Additionally, principal component analysis (PCA) as a data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as a patterns classification technique, have been applied, obtaining good results concerning to discrimination and sensitivity. [Copyright &y& Elsevier]

We present the distribution of relaxation times (DRT) method applied to the electrical impedance spectrum data for improving the differentiation of biological tissues by means of two scenarios, a non-parametric representation and a parametric model. The complex electrical impedance from 1 kHz to 1 MHz was measured for ex-vivo WISTAR rat liver, heart, kidney, lung, muscle, and spleen tissues using a homemade electrical impedance spectroscopy (EIS) instrument and analyzed by the DRT method in a time constant domain revealing a particular non-parametric representation for differentiating each tissue using the retrieved distribution function. A larger number of relaxation time constants are found giving the possibility of studying the different polarization processes related to the tissues. We propose a parametric impedance model associated to DRT in the frequency domain to estimate the complex impedance of EIS measurements. Our results were compared with that obtained by the classical impedance Cole-Cole model. [ABSTRACT FROM AUTHOR]