D. Matatagui

Real-Time Characterization of Electrospun PVP Nanofibers as Sensitive Layer of a Surface Acoustic Wave Device for Gas Detection

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.

Array of Love-wave sensors based on quartz/Novolac to detect CWA simulants.

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 25 ppb 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.

Graphene oxide as sensitive layer in Love-wave surface acoustic wave sensors for the detection of chemical warfare agent simulants

A Love-wave device with graphene oxide (GO) as sensitive layer has been developed for the detection of chemical warfare agent (CWA) simulants. Sensitive films were fabricated by airbrushing GO dispersions onto Love-wave devices. The resulting Love-wave sensors detected very low CWA simulant concentrations in synthetic air at room temperature (as low as 0.2 ppm for dimethyl-methylphosphonate, DMMP, a simulant of sarin nerve gas, and 0.75 ppm for dipropylene glycol monomethyl ether, DPGME, a simulant of nitrogen mustard). High responses to DMMP and DPGME were obtained with sensitivities of 3087 and 760 Hz/ppm respectively. Very low limit of detection (LOD) values (9 and 40 ppb for DMMP and DPGME, respectively) were calculated from the achieved experimental data. The sensor exhibited outstanding sensitivity, good linearity and repeatability to all simulants tested. The detection mechanism is here explained in terms of hydrogen bonding formation between the tested CWA simulants and GO.

Characterization of an array of Love-wave gas sensors developed using electrospinning technique to deposit nanofibers as sensitive layers.

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 0.2 ppm of DMMP, a simulant of sarin nerve gas, and 1 ppm 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.

Love-Wave Sensors Combined with Microfluidics for Fast Detection of Biological Warfare Agents

The following paper examines a time-efficient method for detecting biological warfare agents (BWAs). The method is based on a system of a Love-wave immunosensor combined with a microfluidic chip which detects BWA samples in a dynamic mode. In this way a continuous flow-through of the sample is created, promoting the reaction between antigen and antibody and allowing a fast detection of the BWAs. In order to prove this method, static and dynamic modes have been simulated and different concentrations of BWA simulants have been tested with two immunoreactions: phage M13 has been detected using the mouse monoclonal antibody anti-M13 (AM13), and the rabbit immunoglobulin (Rabbit IgG) has been detected using the polyclonal antibody goat anti-rabbit (GAR). Finally, different concentrations of each BWA simulants have been detected with a fast response time and a desirable level of discrimination among them has been achieved.

Nanocrystalline Tin Oxide Nanofibers Deposited by a Novel Focused Electrospinning Method. Application to the Detection of TATP Precursors

A new method of depositing tin dioxide nanofibers in order to develop chemical sensors is presented. It involves an electrospinning process with in-plane electrostatic focusing over micromechanized substrates. It is a fast and reproducible method. After an annealing process, which can be performed by the substrate heaters, it is observed that the fibers are intertwined forming porous networks that are randomly distributed on the substrate. The fiber diameters oscillate from 100 nm to 200 nm and fiber lengths reach several tens of microns. Each fiber has a polycrystalline structure with multiple nano-grains. The sensors have been tested for the detection of acetone and hydrogen peroxide (precursors of the explosive triacetone triperoxide, TATP) in air in the ppm range. High and fast responses to these gases have been obtained.

Saw Sensor Array for Chemical Warfare Agent Simulants

A surface acoustic wave array of sensors was developed for the detection of chemical warfare agent simulants. Sensors were coated with different polymers for a higher accuracy. Data acquired were processed; Principal Components Analysis (PCA) and Probabilistic Neural Network (PNN) were used for the discrimination and classification of the chemical agents.

Acoustic Sensors Based on Amino-Functionalized Nanoparticles to Detect Volatile Organic Solvents

Love-wave gas sensors based on surface functionalized iron oxide nanoparticles has been developed in this research. Amino-terminated iron oxide nanoparticles were deposited, by a spin coating technique, onto the surface of Love-wave sensors, as a very reproducible gas-sensing layer. The gases tested were organic solvents, such as butanol, isopropanol, toluene and xylene, for a wide and low concentration range, obtaining great responses, fast response times of a few minutes (the time at which the device produced a signal change equal to 90%), good reproducibilities, and different responses for each detected solvent. The estimated limits of detection obtained have been very low for each detected compound, about 1 ppm for butanol, 12 ppm for isopropanol, 3 ppm for toluene and 0.5 ppm for xylene. Therefore, it is demonstrated that this type of acoustic wave sensor, with surface amino-functionalized nanoparticles, is a good alternative to those ones functionalized with metal nanoparticles, which result very expensive sensors to achieve worse results.

Love wave toluene sensor based on multi-guiding layers

A novel Love-wave sensor based on multi-guiding layers, SiO2 layer and indium tin oxide (ITO) nanoparticle layer, was developed. The ITO nanoparticles worked as guiding and sensitive layers at the same time. The interaction between ITO nanoparticles and toluene molecules produced changes in elastic properties of nanoparticles and consequently the sensor suffered a proportional frequency shift for each toluene concentration. The Love wave multi-guiding layer sensor detected concentrations as low as 1 ppm of toluene.

Improving Sensitivity of a Chemoresistive Hydrogen Sensor by Combining ZIF-8 and ZIF-67 Nanocrystals

In the present work, nanostructures of zeolitic imidazolate frameworks (ZIF-8 and ZIF-67) were combined to obtain a novel chemoresistive sensor, improving the sensitivity of ZIF-67 and facilitating measurement of ZIF-8 by decreasing the resistivity. The sensor detected concentrations as low as 10 ppm of hydrogen increasing its resistivity about 4.5 times. The response of the sensor was compared with a similar chemoresistive sensor based exclusively on ZIF-67, and the sensitivity was around three times higher in the case of the sensor with ZIFs combination.