Reliable Chemical Sensors Research Articles

Selective Detection of Toxic C1 Chemicals Using a Hydroxylamine-Based Chemiresistive Sensor Array.

Formaldehyde (FA) is a deleterious C1 pollutant commonly found in the interiors of modern buildings. C1 chemicals are generally more toxic than the corresponding C2 chemicals, but the selective discrimination of C1 and C2 chemicals using simple sensory systems is usually challenging. Here, we report the selective detection of FA vapor using a chemiresistive sensor array composed of modified hydroxylamine salts (MHAs, ArCH2ONH2·HCl) and single-walled carbon nanotubes (SWCNT). By screening 32 types of MHAs, we have identified an ideal sensor array that exhibits a characteristic response pattern for FA. Thus, trace FA (0.02-0.05 ppm in air) can be clearly discriminated from the corresponding C2 chemical, acetaldehyde (AA). This system has been extended to discriminate methanol (C1) from ethanol (C2) in combination with the catalytic conversion of these alcohols to their corresponding aldehydes. Our system offers portable and reliable chemical sensors that discriminate the subtle differences between C1 and C2 chemicals, enabling advanced environmental monitoring and healthcare applications.

Metal Oxide Nanoheterostructures for Gas Sensing

1. Introduction.Metal oxides such as SnO2, MoO3. TiO2, CuO, are well-known to exhibit significant changes in their electrical resistance upon admission of certain oxidizing or reducing chemical species which constitutes the base for their application as gas sensors. These materials can be synthesized in different forms ranging from bulk ceramics to thin films. Thin-film technology has contributed significantly to the development of reliable chemical sensors as it is easily controllable and results in reproducible parameters of deposited layers [1,2]. Moreover, it is compatible with interdigitated transducer IDT electrodes which facilitates film deposition and subsequent electrical contacts with the resistance measuring units [3]. Emerging nanotechnology has led to a revolution in sensing especially as far as different forms of nanomaterials have demonstrated better response, sensitivity and selectivity to different stimuli. Moreover, the nanostructured sensors can operate much faster due to better kinetics of responses at relatively low temperatures, i.e., close to room temperature. The aim of this contribution is to review the most recent work performed in the field of thin film resistive-type gas sensors with a special emphasis on the n-n and n- p nanostructures.2. ExperimentalThin films of different stoichiometry and crystal structures have been deposited by magnetron sputtering of Ti, Sn, and Cu targets in reactive Ar+O2 atmosphere with controlled composition. Characterization of films has been performed by X-ray diffraction XRD, X-ray reflectivity, XRR, X-ray photoelectron spectroscopy XPS, atomic force microscopy, AFM, scanning electron microscopy, SEM and optical spectrophotometry over uv and visible range of the light spectrum. Gas sensing measurements both in dc and ac modes have been carried out in a custom-made set-up capable of detecting changes in the electrical resistance under stabilized temperature and humidity level. Modular XM-MTS unit from Solartron Analytical has been used to detect the impedance spectra in reference atmosphere (air) and upon gas (NO2, H2) admission.3. ResultsExperimental results concerning thin film characterization will be presented and compared with the most representative data obtained by other authors. Fundamental properties of different n-type (TiO2, SnO2) and p-type (CuO) semiconductors will be discussed.Depending on the material being sputtered and the substrate on which a thin film is deposited one can observe a growth of different nanostructures. Typically, a columnar structure is obtained in the case of TiO2 while the amorphous films of SnO2 result in a smooth top SEM image composed of small, isolated grains. CuO thin films crystallize easily with relatively large, well-developed grains.Gas sensor responses are good and reproducible in the case of n-type semiconductors such as TiO2 and SnO2. CuO being a p-type semiconductor demonstrates much lower response which can be improved by forming TiO2/CuO n-p type hetero-structure.

Environment-friendly and highly sensitive dichloromethane chemical sensor fabricated with ZnO nanopyramids-modified electrode

Abstract The effective detection of dichloromethane (DCM) was performed by hexagonal zinc oxide (ZnO) nanopyramids (NPys) modified disposable screen printed electrode (SPE) for the fabrication of reproducible, highly sensitive and reliable chemical sensors. ZnO NPys were synthesized by a simple hydrothermal procedure using zinc acetate as precursor and oleylamine as surfactant. Well-grown hexagonal pyramids like structures were incurred in a high aspect ratio. The optical, structural and the compositional characterizations confirmed a good quality and crystallinity possessing a wide band gap (Eg) of ∼3.29 eV of ZnO NPys. The hexagonal ZnO NPys modified disposable SPE chemical sensor showed a good sensing behavior with a sensitivity of ∼293.5 µA/µM/cm2 and limit of detection (LOD) of ∼17.3 µM toward the detection of DCM. The electrochemical sensor based on hexagonal ZnO NPys modified disposable SPE demonstrated an excellent linearity in the range of ∼100 nM to 200 µM and a good retention coefficient (R) of ∼0.982055 which resulted in good sensing properties.

Detection of trace levels of organophosphate pesticides using an electronic tongue based on graphene hybrid nanocomposites

Organophosphate (OP) compounds impose significant strains on public health, environmental/food safety and homeland security, once they have been widely used as pesticides and insecticides and also display potential to be employed as chemical warfare agents by terrorists. In this context, the development of sensitive and reliable chemical sensors that would allow in-situ measurements of such contaminants is highly pursued. Here we report on a free-enzyme impedimetric electronic tongue (e-tongue) used in the analysis of organophosphate pesticides comprising four sensing units based on graphene hybrid nanocomposites. The nanocomposites were prepared by reduction of graphene oxide in the presence of conducting polymers (PEDOT:PSS and polypyrrole) and gold nanoparticles (AuNPs), which were deposited by drop casting onto gold interdigitated electrodes. Impedance spectroscopy measurements were collected in triplicate for each sample analyzed, and the electrical resistance data were treated by Principal Component Analysis (PCA), revealing that the system was able to discriminate OPs at nanomolar concentrations. In addition, the electronic tongue system could detect OPs in real samples, where relations between the principal components and the variation of pesticides in a mixture were established, proving to be useful to analyze and monitor mixtures of OP pesticides. The materials employed provided sensing units with high specific surface area and high conductivity, yielding the development of a sensor with suitable stability, good reproducibility, and high sensitivity towards pesticide samples, being able to discriminate concentrations as low as 0.1nmolL−1. Our results indicate that the e-tongue system can be used as a rapid, simple and low cost alternative in the analyses of OPs pesticide solutions below the concentration range permitted by legislation of some countries.

SnO2 doped MoO3 nanofibers and their carbon monoxide gas sensing performances

SnO2 doped MoO3 nanofibers with an average diameter of 100nm were synthesized by a wet-chemical method, and sensors were fabricated by screen printing the nanofibers on alumina ceramic substrates. Structural characterizations were carried out using X-ray diffractometer, scanning electron microscope and transmission electron microscope, and chemical state analyses by energy dispersive X-ray spectroscope, X-ray photoelectron spectroscope and Diffuse Reflectance Infrared Fourier Transform Spectroscope. The carbon monoxide (CO) sensing properties were characterized in the temperature range of 200 to 400°C; comparing with α-MoO3, both the sensitivity and the selectivity of the SnO2 doped MoO3 nanofibers were improved. The chemisorption and the oxidation of CO on the surfaces of the nanofibers are vital to the sensing performance; the addition of SnO2 to MoO3 enhanced the chemisorption and the oxidation of CO. The high sensitivity and vigorous repeatability demonstrate that the nanofibers are auspicious as sensitive and reliable chemical sensors.

Microwave-assisted synthesis of ZnO doped CeO2 nanoparticles as potential scaffold for highly sensitive nitroaniline chemical sensor

Herein, we report the successful fabrication of highly sensitive, reproducible and reliable nitroaniline chemical sensor based on ZnO doped CeO2 nanoparticles. The ZnO doped CeO2 nanoparticles were synthesized through a simple, facile and rapid microwave-assisted method and characterized by several techniques. The detailed characterizations confirmed that the synthesized nanoparticles were monodisperse and grown in high density and possessing good crystallinity. Further, the synthesized ZnO doped CeO2 nanoparticles were used as efficient electron mediators for the fabrication of high sensitive nitroaniline chemical sensors. The fabricated nitroaniline chemical sensor exhibited very high sensitivity of 550.42μAmM−1cm−2 and experimental detection limit of 0.25mM. To the best of our knowledge, this is the first report in which CeO2–ZnO nanoparticles were used as efficient electron mediators for the fabrication of nitroaniline chemical sensors. Thus, presented work demonstrates that ZnO doped CeO2 nanoparticles are potential material to fabricate highly efficient and reliable chemical sensors.

An electrochemical sensing platform based on hollow mesoporous ZnO nanoglobules modified glassy carbon electrode: Selective detection of piperidine chemical

Hollow mesoporous ZnO nanoglobules were synthesized through carbon spheres template assisted sonochemical process followed by annealing at 600°C. The synthesized hollow mesoporous ZnO nanoglobules was applied as a working electrode or electron mediator electrode for the fabrication of reproducible, highly sensitive and reliable chemical sensors for the detection of piperidine chemical. The synthesized nanomaterials possessed the porous hollow globular morphology due to the radial arrangement of nanoparticles on the outer shell of nanoglobules. The formation of hollow mesoporous ZnO nanoglobules was confirmed by analyzing the structural, crystalline and the compositional properties. The electrochemical behavior was examined by performing the cyclic voltammetry using hollow mesoporous ZnO nanoglobules based glassy carbon electrode (GCE) towards the detection of piperidine chemical. The performance of piperidine chemical sensor based on hollow mesoporous ZnO nanoglobules GCE was analyzed by measuring the current (I)–voltage (V) characteristics of different piperidine concentrations in phosphate buffer solution. The hollow ZnO nanoglobules GCE based piperidine chemical sensor exhibited the high sensitivity of ∼59.9μAmM−1cm−2 and a detection limit of ∼3.3μM with a correlation coefficient (R) of ∼0.98782 and a short response time of 10s.

Fabrication and Characterization of Smart Chemical Sensor Based on CoAl<SUB>0.</SUB><SUB>7</SUB>Fe<SUB>1.</SUB><SUB>3</SUB>O<SUB>4</SUB> Ferrite Nanoparticles

This paper reports the successful fabrication of phenyl hydrazine chemical sensor based on CoAl07Fe13O4 ferrite nanoparticles. The CoAl07Fe13O4 ferrite nanoparticles were synthesized by simple and facile co-precipitation method and characterized in terms of their morphological, structural, compositional and electrical properties. The detailed characterizations confirmed that the prepared ferrite nanoparticles are grown in nanostructure, possessing CoAl07Fe13O4 composition and spinel structure of cubic phase. The fabricated phenyl hydrazine chemical sensor based on CoAl07Fe13O4 nanoparticles exhibited a high and reproducible sensitivity of ∼32342 Am M −1 cm −2 with the low experimental detection limit of 0.625 mM in a short response time of ∼100 s. The fabricated sensor shows a linear dynamic range from 0.625 mM to 10 mM. This presented work demonstrates that simply prepared CoAl07Fe13O4 ferrite nanoparticles are efficient electron mediators for the fabrication of robust and reliable chemical sensors for the detection of hazardous chemicals.

Synthesis and characterizations of ferrite nanomaterials for phenyl hydrazine chemical sensor applications.

This paper presents the synthesis, characterization and phenyl hydrazine chemical sensing applications of Cd0.5Mg0.5Fe2O4 ferrite nanoparticles. The nanoparticles were synthesized by facile and simple co-precipitation method and characterized in detail in terms of their morphological, structural, compositional and electrical properties. The detailed characterization studies revealed that the prepared nanoparticles are grown in high density, possessing Cd0.5Mg0.5Fe2O4 composition and exhibiting spinel cubic structure. Moreover, the prepared Cd0.5Mg0.5Fe2O4 ferrite nanoparticles were used as efficient electron mediators for the fabrication of high-sensitive, robust, reliable and reproducible phenyl hydrazine chemical sensor by simple I-V technique. The fabricated chemical sensor exhibits a highsensitivity of 7.01 microA mM(-1) cm(-2) with an experimental detection limit of 3.125 mM in a short response time of -10.0 s. This work demonstrates that Cd0.5Mg0.5Fe2O4 ferrite nanoparticles can efficiently be utilized for the fabrication of highly sensitive and reliable chemical sensors.

Porphyrin Supramolecular Aggregates and Chemical Sensors: A Marriage for Smart Devices

The development of smart and reliable chemical sensors has become increasingly important for several application fields, ranging from medical to environmental applications. A chemical sensor is in fact a device that transforms chemical information, ranging from the concentration of a specific sample component to the total composition analysis, into an analytically useful signal. Porphyrins are useful materials for chemical sensors development, since in these devices the porphyrins play the role of receptor, the component that interacts with the chemical environment and for this reason it mostly influences the performances of the device. Since 1995 we have been involved in the preparation of different kind of porphyrin based chemical sensors, for the detection of analytes both in liquid and in the gaseous phase.1 A critical step in the development of such a devices is the deposition of porphyrins as solid layer, because in this process it is necessary from one side to preserve the recognition properties of the single molecules and from the other side take eventually advantage of the additional interaction pathways that the supramolecular organization can offer.2 This latter feature could be furtherly improved by the development of hybrid sensing materials, where the recognition properties of porphyrin aggregates are boosted by the coupling with both inorganic or organic substrates.We have been interested in this approach, developing hybrid materials where porphyrins have been deposited onto ZnO nanorods.3 More recently we have also exploited a simple non-covalent approach to prepare chiral aggregates of poly-lysine, deposited onto a quartz crystal microbalance surface and then used these films as a matrix to form a supramolecular complex with a negatively charged porphyrin, the tetrasulfonatophenylporphyrin (TPPS). This study aims to develop chemical sensors able to perform enantioselective recognition, by functionalization of quartz crystal microbalances (QCM) with chiral supramolecular aggregates. Chemical sensors able to perform rapid and reliable chiral discrimination have an enormous importance for all the fields where the discrimination of enantiomeric pairs is a mandatory task, such as for example drug industry. For this reason the preparation of chiral films is a necessary step, to develop reliable chemical sensors for enantioselective recognition. In this scenario the non-covalent approach can represent a simple way to obtain sensing films featuring chiral properties. We tested the chiral recognition performances of different QCM functionalized with poly-lisine-TPPS films, exposing them to the vapors of some volatile chiral compounds. We studied also in detail the experimental parameters influencing the sensor responses.In the present work we summarise our recent results, showing a promising route for chemical sensors applications.

Detection of organic chemical vapors with a MWNTs-polymer array chemiresistive sensor

Organic chemical hazardous gases pose a significant threat to human life and the environment. An urgent need exists for the development of reliable chemical sensors that would be able to identify these hazardous gases. In a recent study, conductive carbon nanotubes were mixed with six polymers with various chemical adsorption properties to produce a composite thin film for the fabrication of a chemical sensor array. A silicon wafer was used as a microelectrode substrate for a resistance sensor fabricated using a typical semiconductor manufacturing process. This sensor array was then used to identify hazardous chemical gases at various temperatures. Results for two hazardous gases, ammonia (NH3) and chloroform (CHCl3), tested with the six polymers at different temperatures, indicated that the variation in sensitivity/resistance increased when the temperature increased. It was found that the MWNTs-PVP and MWNTs-PMVEMA sensing films had high sensitivity, excellent selectivity, and favorable reproducibility in detecting the two chemical agent vapors. In addition, we derived the solubility parameter (Δδ) to demonstrate the sensitivity of the polymers to ammonia (NH3). The results showed that smaller solubility parameter corresponds to a stronger interaction between NH3 gas and polymers, and increased sensitivity. Additionally, we used the statistical methods of principal component analysis to identify the interaction of hazardous gases with the MWNTs-polymer sensor.

Synthesis of In 2O 3–ZnO core–shell nanowires and their application in gas sensing

Heteronanostructures are very promising gas sensor materials due to their high surface area and hybrid properties. In 2O 3–ZnO core–shell nanowires are synthesized via two-step growth process. The as-deposited shell is made up of grainy polycrystalline ZnO coated on the single crystalline In 2O 3 core. The sensing properties of pristine In 2O 3 and In 2O 3–ZnO core–shell nanowires are investigated for different gases. In 2O 3–ZnO core–shell nanowires are found to possess better response towards the CO, H 2 and ethanol while pristine In 2O 3 nanowires has shown a superior response towards the NO 2. The high sensitivity and dynamic repeatability have shown in these sensors reveal that the core–shell nanowires are promising as sensitive and reliable chemical sensors. The gas sensing mechanism of these heterostructured nanowires is discussed in detail.

Synthesis and Gas Sensing Properties of TiO2–ZnO Core‐Shell Nanofibers

We fabricated TiO2–ZnO core‐shell nanofibers via a novel two‐step process. In the first step, the TiO2 core nanofibers were synthesized by electrospinning. Subsequently, the ZnO shell layers were grown in a controlled manner using atomic layer deposition. The methodology proposed in this work is expected to be one of most suitable methods for preparing various kinds of oxide core‐shell nanofibers or nanowires. We investigated the O2 sensing properties of the synthesized core‐shell nanofibers. Good sensitivity and dynamic repeatability were observed for the sensor, demonstrating that the core‐shell nanofibers hold promise for the realization of sensitive and reliable chemical sensors.

Synthesis of SnO2–ZnO core–shell nanofibers via a novel two-step process and their gas sensingproperties

SnO2–ZnO core–shell nanofibers were synthesized via a novel two-step process. First,SnO2 nanofibers were synthesized by electrospinning. In sequence, ZnO shell layerswere deposited using atomic layer deposition on the electrospinning synthesizedSnO2 nanofibers. To demonstrate the practical applications of the synthesizedcore–shell nanofibers, we investigated their sensing properties toO2 andNO2. The high sensitivity and dynamic repeatability observed in these sensors reveal that thecore–shell nanofibers are promising as sensitive and reliable chemical sensors.

The response of yttria stabilised zirconia oxygen sensors to carbon monoxide gas

Pressures to reduce pollution and conserve fuel have created a growing interest in emission control, highlighting the need for reliable chemical sensors to detect pollutant gases. With particular regard to automotive emission control, this study examines chemical sensors based on yttria stabilised zirconia (YSZ) solid electrolytes for detection and control of carbon monoxide.

Fast Chemical Sensors for Emission Control

Consideration of environmental issues is constantly growing. This brings about a potential market for more sophisticated control of emissions from automobiles and more advanced on-board diagnosis. There is also a growing interest in zero emission power plants and in stricter regulation of other emission sources in industry. One of the important prerequisites for this development is the existence of reliable chemical sensors for combustion control.

Detection of organic solvents with reliable chemical sensors based on cellulose derivatives

Different cellulose derivatives are used as sensitive materials for the detection of different organic solvent vapours by means of quartz-microbalance oscillators and interdigital capacitors. The results show that the sensor responses depend on the temperature-dependent partition coefficients of the organic solvents in the polymers, which are correlated with the Ostwald solubility parameter and the boiling temperature.

Gas sorption to plasma-polymerized copper phthalocyanine film formed on a piezoelectric crystal

Many advances have been made in the last decade in the understanding of the computational principles underlying olfactory system functioning. Neuromorphic Olfaction is a collaboration among European researchers who, through NEUROCHEM (Fp7-Grant Agreement Number 216916)—a challenging and innovative European-funded project—introduce novel computing paradigms and biomimetic artifacts for chemical sensing. The implications of these findings are relevant to a wide audience, including researchers in artifical olfaction, neuroscientists, physiologists, and scientists working with chemical sensors. Developing neuromorphic olfaction from conceptual points of view to practical applications, this cross-disciplinary book examines: The biological components of vertebrate and invertebrate chemical sensing systems The early coding pathways in the biological olfactory system, showing how nonspecific receptor populations may have significant advantages in encoding odor intensity as well as odor identity The redundancy and the massive convergence of the olfactory receptor neurons to the olfactory bulb A neuromorphic approach to artificial olfaction in robots Reactive and cognitive search strategies for olfactory robots The implementation of a computational model of the mammalian olfactory system The book’s primary focus is on translating aspects of olfaction into computationally practical algorithms. These algorithms can help us understand the underlying behavior of the chemical senses in biological systems. They can also be translated into practical applications, such as robotic navigation and systems for uniquely detecting chemical species in a complex background.