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WO 3 has attracted great attention for chemical gas sensing applications. However, the synthesis of WO 3 is mainly performed by using hazardous organic solvents and corrosive acidic solutions, which can result in environmental and health issues. The development of safe synthesis procedures using green compounds and solvents is in great demand to overcome the aforementioned drawbacks. Therefore, the effect of different eco-friendly chemical compounds on the growth of WO 3 materials has yet to be thoroughly studied. Meanwhile, the fabrication of material at the nanoscale with specific crystalline properties may improve its sensitivity to the target gas. In this work, we report an efficient method for the synthesis of WO 3 nanopowder by using water and a green surfactant such as vitamin C. The growth mechanism of the structure is analyzed considering the nature of solutions and surfactants. The studies indicate that the surfactant has a crucial effect on the formation of nanoparticles. Furthermore, the experimental findings show that the fabricated monoclinic WO 3 material is highly sensitive and selective to low concentrations of acetone. Moreover, the structure exhibits quite stable functionalities at different levels of environmental humidity. Hence, this work may have a considerable impact on the existing techniques for the preparation of WO 3 nanomaterials providing new insights into their green synthesis procedures. In addition, it can significantly affect the development of high-performance gas sensors and other catalytic devices based on WO 3 nanostructures. [Display omitted] [ABSTRACT FROM AUTHOR]

The olfactory system is one of the six basic sensory nervous systems. Developing artificial olfactory systems is challenging due to the complexity of chemical information decoding and memory. Conventional chemical sensors can convert chemical signals into electric signals to decode gas information but they lack memory functions. Additional storage and processing units would significantly increase the complexity and power consumption of the devices, especially for portable and wearable devices. Here, an olfactory-inspired in-sensor organic electrochemical transistor (OI-OECT) is proposed, with the integrated functions of chemical information decoding, tunable memory level, and selectivity of vapor sensing. The ion-gel electrolyte endows the OI-OECT with the function of tunable memory levels and a low operating voltage. Typical synaptic behaviors, including inhibitory postsynaptic current and paired-pulse facilitations, are successfully achieved. Importantly, the gas memory level can be effectively modulated by the gate voltages (0 and -1 V), which realized the transformation of volatile and nonvolatile memory. Furthermore, benefiting from the recognition of multiple gases and ability to detect cumulative damage caused by gases, the OI-OECT is demonstrated for early warning system targeting leakage detection of two gases (NH 3 and H 2 S). This work achieves the integrated functions of chemical gas information decode, tunable gas memory level, and selectivity of gas in a single device, which provides a promising pathway for the development of future artificial olfactory systems.

In industrial applications, a functional relationship between the quality characteristics of interest is well represented by profile functions. These are often characterized by linear or nonlinear relationships that depend on the nature of the experimental study. A monitoring method based on linear profiles is known as linear profiling, which is commonly used because of its simplicity. In this article, we propose a new linear profiling method based on a homogenously weighted moving average (HWMA) chart to monitor the linear profile parameters. The HWMA chart is based on the idea of allocating a specific weight to the current estimate of the profiling parameter, and the remaining weight is circulated equally among the prior estimates. The performance of the proposed control chart was evaluated using the average run length criterion and further compared with existing charts for the monitoring of the linear profile parameter. Our simulation results revealed the superiority of the newly proposed chart in terms of its quick detection ability. An example concerning gas sensors fromthe chemical industry is also presented to illustrate the application of the proposed chart. [ABSTRACT FROM AUTHOR]

A newly synthesized calix[4]arene thiourea derivative decorated with 2‐(2‐aminophenyl)benzothiazole unit is selected to take part important role in host‐guest interactions of the macrocyclic molecules. p‐tert‐butylcalix[4]arene dithiourea (C[4]‐DT) Langmuir‐Blodgett (LB) thin films are prepared and characterized to develop a new sensing element for the detection of seven different organic vapors (dichloromethane, chloroform, acetone, benzene, carbon tetrachloride, toluene and m‐xylene). The preparation of C[4]‐DT‐based thin films onto the different substrates was successfully and uniformly achieved with linear regressions of 0.9971 and 0.9954 for coating onto quartz glass and quartz crystal, respectively. The frequency shift (61.01 Hz) and the mass deposited onto quartz crystal (969.80 ng) were calculated for each layer. The swelling dynamics of C[4]‐DT QCM chemical sensor was also illuminated by developing the early time Fick's diffusion equation. The sensing measurements can be concluded that owing to its high sensitivity (6.63 Hz/ppm), fast response and low detection limit (0.45 ppm), this proposed C[4]‐DT LB coated sensor is expected to be promising alternative chemical sensor for detection of DCM vapor. [ABSTRACT FROM AUTHOR]

For many applications, gas sensors need to be very sensitive, selective and exhibit a good stability. Moreover, they should also be cheap and small, and allow a fast response time. Usually, sensors are optimized for specific applications with a compromise between the mentioned criteria. Here, we show a method that allows very sensitive, but rather slow, graphene metal oxide hybrid sensors to be used in a much faster and more effective way with a focus on targeting trace level concentrations of some common toxic air pollutants. By exploiting the first-order time-derivative of the measured resistance signal after a concentration step, the response peak is achieved much faster, while also being more robust against sensor exposure and relaxation times, and concomitantly maintaining the very high sensitivities inherent to graphene. We propose to use this method to generate an additional signal to allow using sensors that are normally rather slow in applications where steep concentration changes need to be detected with much faster time constants.

Sensor drift is one of the important problems affecting the stability of gas sensing detection system.In this paper,a support vector machine (SVM) self-training classification model for online drift compensation is proposed,in which the forgetting factor is introduced to cope with the influence of drift and en sure the balance state of the data set, and the priming factor is introduced to avoid the extreme situation that the model cannot be trained due to the imbalance of the training set. The experimental results show that the improved classification model can extend the reliable service time of the sensor and improve the classification effect in the short and medium term to a certain extent. The self-training process of the model does not require manual participation, which is in line with the practical application scenario. The research ideas and methods put forward in this paper have certain reference significance to the research in related fields. [ABSTRACT FROM AUTHOR]

TiO2 – Fe2O3 composites with iron oxide content in the range of 1–50 mol. % were synthesized by sol-gel method. By means of X-ray diffraction analysis, scanning electron microscopy and IR spectroscopy the dependence of composite structure on the oxide molar ratio and annealing temperature was established. With the use of the synthesized oxide materials semiconductor gas sensors were fabricated. The possibility of low temperature detection of ethanol vapor with sensor at power consumption of 20 mW was shown. Correlation between the gas sensing activity of the composites towards ethanol vapor and structural characteristics of the composites was revealed. The highest output signal value has been attained for TiO2 – Fe2O3 composite with 50 mol. % content of iron oxide heated below 400 °C. This material consists of two oxide phases (anatase and g-Fe2O3 ) and possesses a developed surface.

Carbon dioxide (CO 2 ) is a major greenhouse gas responsible for global warming and climate change. The development of sensitive CO 2 sensors is crucial for environmental and industrial applications. This paper presents a novel CO 2 sensor based on perovskite nanocrystals immobilized on graphene and functionalized with oxygen plasma treatment. The impact of this post-treatment method was thoroughly investigated using various characterization techniques, including Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The detection of CO 2 at parts per million (ppm) levels demonstrated that the hybrids subjected to 5 min of oxygen plasma treatment exhibited a 3-fold improvement in sensing performance compared to untreated layers. Consequently, the CO 2 sensing capability of the oxygen-treated samples showed a limit of detection and limit of quantification of 6.9 and 22.9 ppm, respectively. Furthermore, the influence of ambient moisture on the CO 2 sensing performance was also evaluated, revealing a significant effect of oxygen plasma treatment.

Highly sensitive, stable, low production costs, together with easy maintenance and portability, sensors are ever most demanded nowadays for monitoring and quantification of hazardous chemicals/gases in the environment. The utilization of one dimensional (1D) metal oxide nano structured chemical/gas sensors for environmental monitoring is vastly investigated because of their superior surface to volume ratio, stability, and low production costs, to provide information on the presence of chemical species. Several outstanding attempts have been pursued investigating 1D nano structures of Co3O4 over the past decades as an active material for chemical analytes detection owing to its superior catalytic effect together with its excellent stability. This article reviews the state-of-the-art of growth and characterization of Co3O4 1D nano structures and their functional characterization as chemical/gas sensors. Moreover, fundamental concepts and characteristic features, that enhance the key performances of chemical/gas sensors, are discussed. Finally, challenges and prospective for growth and fabrication of 1D Co3O4 chemical/gas sensors are discussed.

This paper presents an inkjet-printed differential passive microwave planar resonator-based sensor for toxic vapor detection at room temperature. Two devices are presented, with 5 (D1) and 50 (D2) layers of composite sensitive film (PEDOT:PSS-MWCNTs). Each one consists of two band-pass resonators with the fundamental modes around 2.5 and 2.7 GHz. Theoretical and experimental results are presented, both devices show sensitivity to ethanol vapor ranging from 500 to 1300 ppm according to the magnitude and resonant frequency shifts of their scattering parameters (S-parameters). Limitations due to a continuous drift on both the reference and the sensitive channels are discussed. Though further improvements are needed, such sensor is a good candidate for integration into real-time multi-sensing platforms adaptable for the Internet of Things. [ABSTRACT FROM AUTHOR]

In this manuscript, we explore the sensor properties of epitaxially grown graphene on silicon carbide decorated with nanolayers of CuO, Fe3O4, V2O5, or ZrO2. The sensor devices were investigated in regard to their response towards NH3 as a typical reducing gas and CO, C6H6, CH2O, and NO2 as gases of interest for air quality monitoring. Moreover, the impact of operating temperature, relative humidity, and additional UV irradiation as changes in the sensing environment have been explored towards their impact on sensing properties. Finally, a cross-laboratory study is presented, supporting stable sensor responses, and the final data is merged into a simplified sensor array. This study shows that sensors can be tailored not only by using different materials but also by applying different working conditions, according to the requirements of certain applications. Lastly, a combination of several different sensors into a sensor array leads to a well-performing sensor system that, with further development, could be suitable for several applications where there is no solution on the market today.

Highlights • We believe that the presented study provides a new approach to create a highly sensitive and selective sensory nanocomposite to hydrogen peroxide (HP) vapors based on organic chromophore infiltrated in nanoporous multi-layered structure. An attractive feature of our approach is that quinoline-boronate (QIB) exhibits higher quantum yield and faster response time when infiltrated into the nanoporous silicon, as compared with a flat substrate. • The highest sensitivity can be easily attained by the optimal amount of the sensory material infiltrated inside nanoporous silicon. In contrast to other dyes used for hydrogen peroxide vapor detection, which require multi-step synthesis or additional compounds to stabilized fluorescence and increase sensitivity, QIB is photo-stable and commercially available. • We would like to emphasize, that the trace detection of HP vapors is of the utmost of importance for homeland security, as HP can be utilized as a precursor for fabrication of homemade peroxide explosives; however, there are just a few studies about HP trace detection in the vapor phase. Abstract We report the highly sensitive and selective detection of hydrogen peroxide vapors via fluorescence enhancement (turn-on mechanism) for boronate quinoline chromophore deposited on a flat substrate and entrapped in a nanoporous silicon multi-layered structure. The detection limit was determined to be 150 ppt with a negligible response to major volatile organic compounds and water. A distinctive feature is extraordinary sensitivity which critically depends on amount of the sensory material infiltrated inside nanoporous silicon. [ABSTRACT FROM AUTHOR]

The analysis of exhaled volatile organic compounds (VOCs) related to lung cancer is a very promising way in medical diagnosis because it is non-invasive and much less expensive than traditional medical analysis used so far. In that sense, a silicon micro-analytical platform consisting of a micro-preconcentrator coupled to a silicon spiral gas chromatographic micro‐column was built, and a metal oxide-based gas sensor was used as a miniaturized gas detector. This micro-fabricated device was successfully tested to selectively detect low concentrations of VOCs considered as lung cancer biomarkers, within a few minutes even in presence of high concentrations of water vapor and carbon dioxide. [ABSTRACT FROM AUTHOR]

This study presents the feasibility and the first real time results of microwave flexible gas sensor based on poly (3,4-ethylenedioxythiophene) polystyrene sulfonate – multi wall carbon nanotubes (PEDOT:PSS-MWCNTs) as sensitive material, deposited by inkjet printing technology. The sensor is suitable for wireless applications, it consists of two stub resonators on kapton in order to provide a differential detection. The final aim of this work is to develop a low cost communicating sensor which can be integrated into real time multi sensing platform dedicated to the applications requiring low power consumption and adaptable for the Internet of Things (IoT), in order to do the detection of harmful gases such as Volatile Organic Compounds (VOCs). Preliminary results have shown a large influence of ethanol concentration on the electrical properties of the passive resonators at radio-frequency range. These vapors have induced additional insertion losses and frequency shifts on the first resonant frequency mode around 0.65 GHz. The sensor sensitivity to ethanol vapors exposition has been estimated to −642.9 Hz/ppm and −7 μdB/ppm for resonant frequency and insertion losses variations in differential mode, respectively, according to the values at 4 min of exposure to 500, 1000 and 2000 ppm. To deepen the study of the sensor, we have focused on the influence of ethanol on the conductivity of the sensitive layer, in terms of repeatability and sensitivity. We proposed a way of real-time reconstruction of the response by representing the difference of the insertion losses as well as the difference of frequencies calculated on the basis of the phase average value within a specified frequency range near the resonance. This lead to estimate a sensitivity of −9 μdB/ppm and 648.1 Hz/ppm, respectively, for ethanol concentrations ranging from 500 ppm to 2000 ppm at 10 min of exposure. [ABSTRACT FROM AUTHOR]

We have obtained and studied the sensing properties of porous titania-based nanostructures. The materials have been prepared using cost-effective techniques. The morphological and structural analyses of the prepared materials have been performed. The sensing properties of the samples have been studied towards carbon monoxide. The obtained results demonstrate that the prepared structures are promising for the potential applications in the area of chemical sensors for the environmental monitoring.

Due to high porosity and increased surface area; metal organic frameworks (MOFs) have been widely used in gas storage applications as well as volatile organic compounds (VOCs) detection. Most of these sensors are electromechanical or electrochemical based; however there are few works in which capacitive sensors were developed using micrometer MOFs. In the present study, for the first time, MOF (Cu-BTC) nanoparticles were used to develop capacitive sensor device for detecting VOCs (e.g. methanol, ethanol, isopropanol, and acetone). The studied capacitive sensors were performed in a moderate environment (10% relative humidity and 25 °C). Capacitive sensors were fabricated in a sandwich form or parallel plate by using copper plate as a back electrode, MOF nanoparticles layer as the dielectric, and interconnected silver spots as the upper electrode of the capacitor. Linearity of the response versus LCR meter frequency, reusability, reversibility, response time, and limit of detection (LOD) of the capacitive sensor were determined to evaluate the sensor performance. The results showed high ability of Cu-BTC nanoparticles synthesized as dielectric layer of a capacitive nanosensor to determine VOCs. [ABSTRACT FROM AUTHOR]

Phthalocyanines are well-established sensing materials for chemical sensors such as quartz crystal microbalance (QCM), surface acoustic wave, or conductive sensors due to their superb sensing qualities and the wide manifold in their sorption properties. The sensing characteristics are determined by the metal ion center and substituents attached to the periphery of the ring system. In this work, a novel method to change the sorption characteristics of phthalocyanines and thereby to govern sensor sensitivity and selectivity is presented by using axial ligands attached to phthalocyanines with a suitable metal ion center. This has been proven to be a simple method to create a library of compounds having very diverging sensing properties using a single base compound. Fourteen axially substituted titanium phthalocyanines were tested using the QCM in their responses to vapors of selected volatile compounds including DMMP. Generally, the axially substituted phthalocyanines have shown excellent sensor characteristics. It was found that the axial ligand has a strong influence on the sensor responses and selectivity for certain analytes was achieved. The use of axial ligands to govern the sensing features of phthalocyanines is considered a promising approach for sensitive material development and advantageous due to the rather simple preparation method. [ABSTRACT FROM AUTHOR]

Poly(3-methylthiophene) (PMeT) thin films were electrochemically deposited on quartz crystal microbalance QCM transducers to investigate their volatile organic compound (VOC) sensing properties depending on ambient conditions. Twelve different VOCs including alcohols, ketones, chlorinated compounds, amines, and the organosphosphate dimethyl methylphosphonate (DMMP) were used as analytes. The responses of the chemical sensors against DMMP were the highest among the tested analytes; thus, fabricated chemical sensors based on PMeT can be evaluated as potential candidates for selectively detecting DMMP. Generally, detection limits in the low ppm range could be achieved. The gas sensing measurements were recorded at various humid air conditions to investigate the effects of the humidity on the gas sensing properties. The sensing performance of the chemical sensors was slightly reduced in the presence of humidity in ambient conditions. While a decrease in sensitivity was observed for humidity levels up to 50% r.h., the sensitivity was nearly unaffected for higher humidity levels and a reliable detection of the VOCs and DMMP was possible with detection limits in the low ppm range. [ABSTRACT FROM AUTHOR]

The objective of the present paper is to provide a concept for a chemical sensor having a small size, a low power consumption and a high reliability for sensing CO2 under different humidity levels at atmospheric pressure, while maintaining a long term stability under working conditions. A high temperature regeneration process of the sensing layer is unneeded to ensure a long term stability of the sensing material. This objective is achieved by using a hybrid organic-inorganic nanomaterial, consisting of inorganic nanoparticles functionalized with an amine-based polymer.

This communication presents results on the feasibility of an inkjet printed chemical gas sensor suitable for a real time multi-sensing platform. The prototype targets volatile organic compounds (VOCs) such as ethanol vapor to monitor environmental pollution. The designed and ink-jet printed microwave sensor is presented. Preliminary results have shown the influence of ethanol vapor on the electrical properties of the sensor at microwave frequency range. The sensor’s sensitivity to ethanol vapor has been estimated to −2.48 kHz/ppm. The final aim of this work is to develop a low cost sensor for Internet of Things (IoT) applications.

The sensory response of nanostructured In 2 O 3 + CeO 2 composite films to hydrogen and carbon monoxide in air ambience is investigated for varying film composition and temperature ranging from 280 °C to 520 °C. The temperature dependence of the sensor response S ( S = R 0 / R , where R 0 and R are respectively the film resistance in pure air and air containing the sample gas), exhibits the trend typical of such sensors, specifically, curves with maximum S max at a certain temperature T max . The values of S max , characterizing the sensor response of the films significantly increase when a small amount of CeO 2 is added to In 2 O 3 . Addition of CeO 2 to In 2 O 3 also results in a decrease in T max . The measured XPS spectra show that at low CeO 2 composition, the composite film structure is characterized by clusters with a high concentration of oxygen vacancies, which increase the chemisorption of reagents and oxygen. The maximum sensor response is observed in In 2 O 3 + CeO 2 composite films containing 3–10 wt.% CeO 2 . Further enrichment of the composite with CeO 2 produces a sharp decrease in sensor response, which at 40 wt.% CeO 2 is less than the response of pure In 2 O 3 . The response mechanism in the In 2 O 3 + CeO 2 composite is also investigated, considering the promotion of sensory reactions by small CeO 2 nanoclusters located on the surface of the In 2 O 3 nanocrystals. [ABSTRACT FROM AUTHOR]

In this study we deposited new, ternary thin films of copper aluminum oxide with p -type and n -type behavior using RF magnetron sputtering for use as chemical gas sensors. p -Type materials are known to be good catalysts and can be combined with the well-known n -type materials for chemiresistive sensors application. Copper aluminum oxide in the delafossite phase CuAlO 2 is a ternary oxide that has generated interest as a transparent p -type conducting material, while in the spinel phase CuAl 2 O 4 is known to be n -type. We demonstrated that thin films of copper aluminum oxide with the proper resistance can be successfully applied as p - and n -type resistive gas sensors for ozone detection. We have studied the sputtering deposition conditions from a CuAlO 2 sintered target by changing the substrate temperature in inert Ar atmosphere. In addition, post-deposition annealing in O 2 atmospheres was also tested. XRD, SEM and Raman investigations were used to characterize the thin films. Selected films with mixed phases of CuAlO 2 , CuAl 2 O 4 and CuO were tested for gas sensing as resistive chemical sensors, showing promising results with ozone, acetone and ethanol. [ABSTRACT FROM AUTHOR]

In this work, we propose to use a screen-printed piezoelectric cantilever with double transduction. Indeed, the piezoelectric cantilever is used as a resonant type sensor coated with carbon nanotubes (CNTs) as sensitive layer. Then, the resistance of CNTs is measured in static mode in parallel thanks to a modification of the cantilever top electrode. The combination of the CNTs equilibrium conductivity measurement and the resonance frequency shift of the 31-longitudinal mode allows the use of this device as a chemical gas sensor for benzene detection. The responses towards benzene concentrations under different relative humidity backgrounds are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Vic-dioximes and their nickel and palladium complexes were customized with fluorinated substituents including moieties capable of hydrogen bonding to improve selectivity in chemical sensing of polar analytes. Many analytes of interest in applications as diverse as food stuff or air quality analysis are of polar chemical nature. Such compounds, e.g., ketones, esters or alcohols contribute to the aroma of fruits and food products, but are also in industrial use as solvents in paints or in the production of plastic products. The gas sensing properties of the new compounds are demonstrated using the quartz crystal microbalance and selected volatile organic compounds as analytes. The results illustrate that fluorinated alkylamino and arylamino substituents efficiently enhance and direct the sorption preferences of vic-dioxime metal complexes toward polar analytes. High sensor responses to polar analytes including high vapor pressure analytes like acetone and methanol were observed, whereas the responses to aromatic hydrocarbons are low. Besides, the individual sensor responses were only little affected by water vapor. H bonding activities of the NH group are identified as the source for the observed selectivity patterns. The vic-dioximes are considered excellent sensing materials for practical use in chemical gas sensor arrays for sensing of polar compounds. [Copyright &y& Elsevier]

Abstract: Metal complexes of vic-dioximes are characterized as new candidate materials for volatile organic compound sensing with sorption based chemical gas sensors. They are proposed as an interesting alternative to conventional sensing materials with metal ion centers such as phthalocyanines or porphyrins. Besides, they are considered an appealing platform to study metal effects on analyte sorption and sensor performance due to a high variety in possible metal centers. In this work, the sensing properties are explored with the quartz crystal microbalance on the basis of a set of vic-dioximes complexes varied in their metal ion centers (Ni2+, Pd2+, Cu2+, Co2+) and substituents (alkyl chain lengths from C3H7 up to C7H15) and twelve selected analytes. Depending on the metal center and substituents widely diverging selectivity patterns were observed indicating preferences for alcohols, amines, and aromatic compounds. The results presented in this work show that the proposed metal complexes of vic-dioximes are excellent sensing materials and very promising for the use in chemical gas sensor array applications. [Copyright &y& Elsevier]

Abstract: Tin–copper mixed metal oxide nanowires were successfully prepared by thermally oxidizing electrodeposited metallic nanowires (Sn–8at.% Cu, Sn–43at.% Cu and Sn–86at.% Cu). The structure and composition of these nanowires before and after thermal oxidation were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD). Dielectrophoresis was utilized to align the nanowires in contact with pre-fabricated interdigitated electrodes to form a chemiresistive gas sensor circuit. The sensitivity variation of the nanowires with different compositions was tested with acetone, ethanol and ethyl acetate vapors at different concentration levels, and the temperature effect was studied at five operating temperatures, ranging from 200°C to 440°C. All the three mixed metal oxide nanowire sensors exhibited higher sensitivity than that of pure tin oxide nanowire sensor. The sensor performance was also investigated in terms of response/recovery time and repeatability. An interesting positive/negative response was observed by varying the element composition of the mixed oxide nanowires. [Copyright &y& Elsevier]

Abstract: Vic-dioximes, a class of organic chemical compounds, are proposed and characterized for the first time as sensitive materials for volatile organic compound sensing with sorption based chemical gas sensors. Their peculiar sensing properties described in this work originate in the oxime functional group which is a powerful H bond donor interacting strongly but reversibly with H bond acceptors. These specific interactions result in a high preferential enrichment of analyte molecules with H bonding acceptor capabilities in the sensitive material. Accordingly, sensitivity and selectivity for these compounds of vic-dioxime based sensors are high. The advantageous sensing properties are demonstrated in this work with quartz crystal microbalance sensors using 11 selected volatile organic compounds and a set of vic-dioximes varied in their substituents. Vic-dioximes with short alkylthiol substituents were found highly sensitive to such H bond acceptors as organic amines, alcohols, and esters with partition coefficients up to 26,000. At the same time they showed low affinity for aromatic compounds and chlorocarbons. Vic-dioximes are considered powerful sensing materials and interesting for practical use in chemical gas sensor arrays. [Copyright &y& Elsevier]

Abstract: Ni(II) and Zn(II) phthalocyanines (Pcs) having fluorinated and non-fluorinated alkyl and aryl oxy substituents were synthesized and characterized as sensitive coatings for chemical gas sensors, namely quartz crystal microbalance (QCM) and surface acoustic wave sensors. The materials are highly suitable for the detection of the organophosphate class of chemicals like dimethyl methyl phosphonate (DMMP). DMMP is not only used as a simulant for nerve agents such as sarin, but also constitutes an interesting target analyte in many other application fields. The fluorinated substituents attached to the Pc core increase the affinity for polar compounds of the Pc molecule resulting in the observed high sensitivity for organophosphates being polar molecules. The octakis(2,2,3,3-tetrafluoropropyloxy) substituted ZnPc shows the highest sensitivity towards DMMP among the tested materials with detection limits below 100ppb. At the same time the influence of background humidity on the sensor signal is very low and the cross-sensitivity values to possible interferents contained in ambient air are 1000times lower. The presented results demonstrate the viability of the new phthalocyanine compounds as highly sensitive and selective materials for detection of DMMP. [Copyright &y& Elsevier]

Abstract: The gas sensing properties of purpose-made phthalocyanines (Pcs) having fluoroalkyloxy, fluoroaryloxy, or non-fluorinated alkyloxy substituents are described. Fourteen Pcs with Ni and Zn metal centers were synthesized systematically changing substituents and substitution pattern. A high sensitivity for polar volatile organic compounds (VOCs) is intended, which is a group of chemicals that is usually less accessible for Pcs as sensing material. Especially, octa fluoroalkyloxy substituted Pcs are very sensitive to polar compounds such as ethyl acetate or acetonitrile. Partition coefficients as high as 5000 are a proof of a high enrichment of these compounds in the sensitive layer. The concept is demonstrated using quartz crystal microbalance (QCM) sensors and twelve VOCs as analytes representing common chemical classes and covering a wide range of chemical properties. Besides, through combination of conventional alkyloxy substituted Pcs with ones having the new fluoroalkyloxy substituents a sensor array with very diverging responses can be created. As the described Pcs are readily available via standard synthesis procedures this is a simple, but effective approach to extend the sensing capabilities of Pcs making them even more attractive as sensitive materials in the use of sorption based chemical sensors, not only the QCM, but also other acoustic transducers. [Copyright &y& Elsevier]

Abstract: This study focused on the detection of vapours of 2, 4, 6 trinitrotoluene (TNT), 2, 4 dinitrotoluene (DNT) and pentaerythrite tetranitrate (PETN) with quartz crystal microbalances operated at 100 MHz. In the selected configuration of the multi-sensors chamber, the behaviour of 4 coated QCM sensors was shown to be equivalent in presence of explosive vapours, which is a major requirement for a multi-sensors system. The high sensitivity and selectivity of the QCMs operated at 100 MHz were demonstrated. The detection signals measured with polypentiptycene coated QCMs in presence of TNT and PETN vapours were considerably increased in comparison with 9 MHz QCMs. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a low temperature sensor with a dual function property is fabricated by using 3–4nm SnO2 quantum dots (QDs) prepared by sonication-assisted precipitation. The sensor shows high selectivity to CO in the presence of methane below 375°C. SnCl4 aqueous solution was precipitated by ammonia under sonication, which continued for 1, 2 and 3h. A part of the sample was then dried and calcined at 400°C for 1.5h and characterized by XRD and BET. UV–vis analyses were carried out for band gap measurements. The average particle size and the specific surface area of the SnO2 QDs as well as their sensing properties were compared with the SnO2 nano-particles prepared by conventional sol–gel method. The BET surface area of sonochemically as-prepared product after 2h sonication and the one calcined at 400°C after 1.5h are 257 and 212m2/g, respectively while the specific surface area for SnO2 prepared by conventional sol–gel method is about 80m2/g. XRD spectra revealed pure crystalline phase of SnO2 is formed for both as-prepared and calcined samples of SnO2 QDs. However, for the sample prepared by sol–gel method and calcined at 400°C, SnO crystals are detected along with the SnO2 crystals. Band gap measurements for the sample fabricated by sonochemical method and calcined at 400°C indicated band gap energy of 5.7eV which shows 2.1eV blue-shift (shift into smaller wave lengths) from that of the bulk SnO2 which was reported earlier by others. Quantum dots of SnO2 show exceedingly high response to different concentrations of 100, 300 and 1000ppm of CO in a temperature range of 25–350°C. At about 50°C a response of 27 was obtained for 1000ppm CO, which increases to a maximum of 147 at 225°C and then decreases whereas the maximum of 47.2 was detected for the SnO2 sample prepared by the sol–gel method occurred at about 300°C. At the same time no response to methane is observed in the whole range of temperatures for SnO2 QDs. On the other hand the response to methane is higher than that to CO at above 375°C. [Copyright &y& Elsevier]

A miniature (millimeter-scale) synthetic jet actuator is integrated with a chemical gas sensor (chemFET) to effect inhalation and exhalation of ambient gas samples and induce small-scale mixing at the surface of the sensor. The fluidically integrated jet transports ambient fluid into the jet/sensor assembly through integrated fluid channels, impinges the sample fluid on the sensing element, and finally ejects the sample fluid to the ambient. The response of the sensor in the presence of the active jet is compared to its response when the jet is inactive. The jet actuator directs entrained ambient air toward the active surface of the sensor, and the impingement of sample gas onto the surface of the sensor results in faster response time. Because the operating characteristics of the integrated synthetic jet actuator can be easily optimized for specific configurations, it is concluded that jet-assisted sampling and sample transport coupled with turbulent impingement can offer significant advantages for gas sensor systems [ABSTRACT FROM PUBLISHER]

Abstract: Nanostructured thin films based on indium oxide have been prepared by a modified rheotaxial growth and thermal oxidation (RGTO) deposition technique. The layers were additivated with 8–30% iron in order to stabilize the microstructure and to enhance the sensing properties toward ozone. Microstructural characterization highlighted formation of core–shell structures featuring iron segregation in the outer part of the nanosized agglomerates. Such peculiar morphology resulted in improved gas sensing performance. The electrical test of the sensing layers indicated high sensitivity to ozone together with a relatively low cross-sensitivity to interfering gases. [Copyright &y& Elsevier]

Abstract: We have designed, manufactured and measured performance of novel chemical gas sensors, which are based on conductivity modulation of discontinuous gold films on a dielectric substrate. The sensor elements were functionalized with different calixarenes. Several volatile analytes were exposed and dynamical sensor responses were investigated. Physical principles of the sensor operation are discussed. Our results show applicability of the proposed approach for chemical sensing and recognition. [Copyright &y& Elsevier]

A micro chlorine gas sensor with an inner-circulation diffuser pump is newly developed. The sensor based on electro-chemical principle, only has the size of one-tenth in comparison with the conventional one. The sensor consists of an air–liquid separation membrane, a PZT-driven diffuser pump and micro electrodes which were manufactured by micro machining. The inner-circulation is generated by driving the diffuser pump with trapped air working as a buffer, in order to preserve the condition of internal reagent. The properties of the sensor were evaluated by circulation rate of the pump, pressure-proof of the membrane, and responsibility to chlorine gas. [Copyright &y& Elsevier]

This paper reports performance characteristics of an electrochemical sensor for CO2 monitoring. The sensor is based on yttria-stabilised (10 mol% Y2O3) cubic zirconia (as a solid electrolyte) and equipped with a CO2 sensing electrode (made of the mixture of carbonates), and Pt reference electrode exposed to air. The sensor performance at 691.6 K is characterised by a stable sensing signal within 5 months. Its response time is 60 s. [Copyright &y& Elsevier]

Highly sensitive, stable, low production costs, together with easy maintenance and portability, sensors are ever most demanded nowadays for monitoring and quantification of hazardous chemicals/gases in the environment. The utilization of one dimensional (1D) metal oxide nano structured chemical/gas sensors for environmental monitoring is vastly investigated because of their superior surface to volume ratio, stability, and low production costs, to provide information on the presence of chemical species. Several outstanding attempts have been pursued investigating 1D nano structures of Co3O4 over the past decades as an active material for chemical analytes detection owing to its superior catalytic effect together with its excellent stability. This article reviews the state-of-the-art of growth and characterization of Co3O4 1D nano structures and their functional characterization as chemical/gas sensors. Moreover, fundamental concepts and characteristic features, that enhance the key performances of chemical/gas sensors, are discussed. Finally, challenges and prospective for growth and fabrication of 1D Co3O4 chemical/gas sensors are discussed. [ABSTRACT FROM AUTHOR]