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Highlights • A new type NiO decorated SnO 2 vertical-standing nanotubes composite thin film was synthesized via a facile hydrothermal method. • Numerous SnO 2 vertical-standing nanotubes with the size of 200–300 nm in diameter and 1.5 μm in length formed a porous microstructure. • NiO nanoplates with the size of 20 nm in diameter decorated on the inside or outside surface of SnO 2 nanotubes formed a heterojunction structure. • The NiO/SnO 2 thin film gas sensor with an Ni2+/Sn4+ molar ratio of 5% exhibited excellent response characteristics to ethanol at 250 ℃. Abstract In this work, a new type NiO decorated SnO 2 vertical-standing nanotubes composite thin film was synthesized successfully via a facile hydrothermal method. The microstructure, physico-chemical surface state and morphology of the composite thin film were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. The results showed that the NiO decorated SnO 2 vertical-standing nanotubes composite thin film with a coral-like microstructure was built of numerous 1D SnO 2 nanotubes with the size of 200–300 nm in diameter and 1.5 μm in length; while NiO nanoplates with the size of 20 nm in diameter decorated on the surface of SnO 2 nanotubes. Due to the enhanced adsorption of oxygen molecules, formation of p -NiO/ n -SnO 2 heterojunction and porous structure, the NiO/SnO 2 thin film gas sensor with an Ni2+/Sn4+ molar ratio of 5% exhibited high response value, good selectivity and quick response characteristics to ethanol at the optimum working temperature of 250 ℃. [ABSTRACT FROM AUTHOR]

Hydrogen is an important biomarker for the human digestive system. However, accurate detection of ppm-level hydrogen in breath is difficult due to the competing detection of high concentration water. We fabricated Pt thin films that respond to hydrogen in air at concentrations as low as 500 ppb. In both dry and humid air, these films have almost identical response to hydrogen, i.e., their resistance decreases linearly with increasing hydrogen concentration regardless of relative humidity. Even at high relative humidity, these Pt thin films can detect ppm-level hydrogen. Furthermore, it was strongly suggested that these films can be applied to low-level hydrogen in the air expired by a healthy human. Based on the chemical kinetics, namely the adsorption and desorption of hydrogen and oxygen, the sensor response is quantitatively described by relating the hydrogen surface coverage to the magnitude of electron scattering at the Pt surface. The proposed model successfully reproduces the effects of hydrogen concentration and time on the sensor response, particularly at hydrogen concentrations below 20 ppm. Based on this model, these Pt thin film sensors have the potential to detect 1 ppm hydrogen in expired air within 30 s. [ABSTRACT FROM AUTHOR]

In this paper we report on the development of an aerosol jet printed sensing platform integrating elements of silicon and printed electronics. To demonstrate the technology, thin film humidity sensors have been fabricated over the top surface and sides of pre-packaged integrated circuits using a combination of direct-write aerosol jet deposition and drop-casting. The resistive based sensor consists of an aerosol jet deposited interdigitated nano-particle silver electrode structure overlaid with a thin film of Nafion ® acting as a humidity sensitive layer. The fabricated sensor displayed a strong response to changes in relative humidity over the tested range (40% RH–80% RH) and showed a low level of hysteresis whilst undergoing cyclic testing. The successful fabrication of relative humidity sensors over the surface and pins of a packaged integrated circuit demonstrates a new level of integration between printed and silicon based electronics – leading to Printed-Sensor-on-Chip devices. Whilst demonstrated for humidity, the proposed concept is envisaged to work as a platform for a wide range of applications, from bio-sensing to temperature or gas monitoring. [ABSTRACT FROM AUTHOR]

We report the development of a novel label-free electrochemical aptasensing platform to detect prostate specific antigen (PSA) based on mesoporous silica thin film-coated gold electrodes as a sensing interface. The aptasensing approach relies on hindering the diffusion of [Fe(CN) 6 ] 3/4− redox probe through the nanochannels of the mesoporous film gated by the recognition of the target biomarker by its anti-PSA specific DNA aptamer covalently attachment onto the outer surface of the silica nanopores. The aptasensing platform was found to be very sensitive to PSA in the range from 1 to 300 ng mL −1 with a detection limit of 280 pg mL −1 . The aptasensor also showed high specificity, reproducibility and storage stability, and was successfully validated in spiked artificial urine samples and in blood serum from a prostate cancer-free male patient. [ABSTRACT FROM AUTHOR]

The application of conventional tin oxide thin film sensors is limited by its low response. In this study, a heterojunction thin film composed of nickel oxide deposited by electron beam evaporation and tin oxide prepared by radio-frequency (RF) magnetron sputtering has enhanced gaseous ethanol sensing properties. The 5 nm NiO/100 nm SnO 2 gas sensor shows the excellent response 7.9 at 250 °C for 100 ppm gaseous ethanol, good reproducibility, as well as good linearity. In addition, this sensor can measure the ultra-low concentration of gaseous ethanol, and the concentration can be as low as 100 ppb. The gas sensitive properties is related to the thickness of nickel oxide and the mechanism is discussed. [ABSTRACT FROM AUTHOR]

Flower-like Bi 2 MoO 6 microspheres, consisting of closely packed nanoparticles, were grown in-situ on ceramic tubes via a simple solvothermal route. Morphology and structure of the flower-like Bi 2 MoO 6 microspheres were characterized by X-ray diffraction meter (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray photoelectron spectroscope (XPS). The microspheres diameters are around 200 nm constructed by nanosheets. Gas-sensing properties of the flower-like Bi 2 MoO 6 microspheres sensors were also systematically investigated. This sensor exhibited an excellent H 2 S sensing performance, including low detection limit of 0.1 ppb, good selectivity, high sensitivity and stability to H 2 S at 170 °C. Such superior H 2 S sensing property might be resulted from the unique structure and good crystallization of Bi 2 MoO 6 microspheres. [ABSTRACT FROM AUTHOR]

The first steps in the development of an aptasensor for bacterial meningitis diagnosis in real time are described: slow off-rate modified aptamers (SOMAmer) selection, gravimetric sensor fabrication and functionalization of its active surface. SOMAmers polyclonal populations were generated to surface specific proteins PavA ( S. pneumoniae ) and FHbp ( N. meningitidis ) by systematic evolution of ligands by exponential enrichment method (SELEX). After eight rounds, they were tested by direct enzyme-linked oligonucleotide assays (ELONA) and by high frequency (1.4 GHz) gravimetric sensors based on thin film AlN resonators operating in shear mode. The sensing surface of the resonators was functionalized using a silane-glutaraldehyde based protocol and the binding of PavA and FHbp was measured in real time. The SOMAmers polyclonal populations showing the best ELONA results have been also tested using gravimetric sensors and the binding to the protein functionalized surface was measured in real time showing positive results. These first steps towards the development of an aptasensor for the targeted bacteria demonstrate the potential of the method for sensitive, rapid, and cost effective detection of bacterial meningitis. [ABSTRACT FROM AUTHOR]

This work describes the fabrication of humidity sensors by depositing black phosphorous (BP) nanosheets (prepared by liquid exfoliation of bulk BP) onto a quartz crystal microbalance (QCM) in the form of a thin film. The surface morphology of the prepared BP nanosheets is characterized using a field-emission scanning electron microscope and transmission electron microscopy. The humidity sensing characteristics of the BP-based QCM sensors (such as frequency response, stability, humidity hysteresis, and repeatability) are investigated by using an oscillating circuit method. Experimental results indicate that the BP-based QCM sensors exhibit a well-defined logarithmic frequency response to humidity, and the sensitivity of the sensor is strongly related to the amount of BP nanosheets used in the deposition process. Additionally, the BP-based QCM sensors exhibit high stability over the wide relative humidity range of 11.3%–84.3% RH. The BP-based QCM sensors also exhibit little humidity hysteresis and fast dynamic response and recovery times. This work demonstrates that BP is a promising candidate material for humidity detection when combined with a QCM transducer. [ABSTRACT FROM AUTHOR]

This paper presents a miniaturized calcium ion-selective solid-state impedance sensor which can be used to measure Ca 2+ in the presence of Mg 2+ and Na + . A novel approach consisting of an ionophore-based Ca sensor combined with a conductivity sensor is used to take one of a wide variety of physical and chemical measurements in potable water. The sensors permit a relatively fast conditioning time. Their design and performance are described. The sensors utilize electrochemical impedance spectroscopy. The advantages are miniaturization and the potential for large-scale production. [ABSTRACT FROM AUTHOR]

This paper presents the experimental work on the sensitivity enhancement of porous aluminium oxide based capacitive humidity sensor for trace moisture measurement. The pore morphology of nanostructured Al 2 O 3 sensing film has been tuned by adding the different amount of polyethylene glycol (PEG) in the sol solution. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Bruner–Emmet–Teller (BET) were performed for pore morphology analysis of thin films prepared by sol–gel technique. Three parallel plate capacitive sensors with identical geometries but different pore morphologies have been fabricated on Fluorine doped Tin Oxide (FTO) substrate and experimented to analyze the effects of PEG addition. The electrical characterization of the sensors has been performed to determine sensitivity, hysteresis, response and recovery time using Agilent 4294A impedance analyzer with frequency range of 1–1000 kHz. It has been observed that the addition of suitable amount of PEG improves the electrical characteristics of the sensor significantly in the range of 10–210 ppm moisture. Response characteristics of the sensors are highly linear ( R 2 = 0.995) and the sensitivity is almost twice in comparison to a sensor without PEG addition. [ABSTRACT FROM AUTHOR]

Large-scale production of reliable carbon nanotubes (CNTs) based gas sensors involves the development of scalable and reliable processes for the fabrication of films with controlled morphology. Here, we report for the first time on highly scalable, ultrathin CNT films, to be employed as conductometric sensors for NO 2 and NH 3 detection at room temperature. The sensing films are produced by dip coating using dissolved CNTs in chlorosulfonic acid as a working solution. This surfactant-free approach does not require any post-treatment for the removal of dispersants or any CNTs functionalization, thus promising high quality CNTs for better sensitivity and low production costs. The effect of CNT film thickness and defect density on the gas sensing properties has been investigated. Detection limits of 1 ppm for NO 2 and 7 ppm for NH 3 have been achieved at room temperature. The experimental results reveal that defect density and film thickness can be controlled to optimize the sensing response. Gas desorption has been accelerated by continuous in-situ UV irradiation. [ABSTRACT FROM AUTHOR]

The antimony-doped tin oxide thin films for gas sensors were prepared via a sol–gel route on alumina substrates. The influence of the antimony addition amount on the electrical resistance of thin films was concluded. The relationship between them was plotted in the coordinates of logarithmic resistance against doping amount. On the basis of the Schottky barrier model, a novel method was used to evaluate the width of depletion layer of semiconductive gas sensors by using the first-order derivative of logarithmic resistance with respect to doping amount. The values of the depletion layer width were calculated for the antimony-doped thin films. The H 2 S gas was used to examine the sensor properties, which positively correlated to the depletion layer width. The oxygen species of O 2− and O − were determined to be the adsorbates on SnO 2 grains with the same proportion at the operating temperature of 300 °C. The location of the Fermi level was found to be a crucial factor that dominated the calculation results. [ABSTRACT FROM AUTHOR]

Chemiresistive MOS-based acetone sensing device is a futuristic pathway for non-invasive diagnosis of diabetes. Although their potential deployment is restricted till now due to lack of selective, low temperature operated ppm-level sensors. In this work, we demonstrated synthesis of iron doped reduced graphene oxide (rGO) decorated WO 3 nanocomposites in a facile, environment friendly wet chemical sol-gel process. The as-synthesized nanocomposites were comprehensively characterized by using different characterization techniques. A maximum ~78% sensing response was obtained for the optimized composition of ~10 wt% Fe doped 3 wt% rGO decorated WO 3 based thin film (thickness ~700 nm) sensor towards ~10 ppm acetone gas. This sensing performance was observed at comparatively low working temperature of ~130 °C with fast response (~20 s) and recovery (~75 s) time. The efficacy of the fabricated sensors was established by their capabilities to sense a very low concentration of ~1 ppm acetone under similar working environment. Further illustration of versatility of the sensors revealed that, the sensors could be able to manifest a repeatable and reproducible sensing performance with prolong stability and superior selectivity for acetone over other interfering gases. The acetone sensing mechanism was illustrated with the help of electron depletion model and impedance spectroscopy study. Impedance spectroscopy quantifies different electrical properties and enlightens the smooth electronic transition mechanism between analyte and sensing material. [Display omitted] • Novel Fe doped reduced graphene oxide (rGO) decorated WO 3 nanocomposite was prepared using a facile sol-gel procedure. • Fabricated Taguchi type thin film sensor exhibited ~ 78 % sensing response towards ~10 ppm acetone at 130°C. • The sensor was also capable to detect very low concentration (~1 ppm) of acetone with fast response and recovery time. • The sensor revealed reproducible performance over time with minimum interference from other interfering gases. • Impedance spectroscopy was used to analyze the sensing mechanism with comprehensive illustration of electrical properties. [ABSTRACT FROM AUTHOR]

Thin films of indium tin oxide (ITO) were deposited using thermal evaporation technique. Various sets of thin film sensors were prepared under the optimized fabrication conditions. The response of the sensors to the quantitative presence of toluene was studied. The sensing mechanism to explain the redox reactions on the surface of ITO film was developed. The films were coated with thin layers of metals and oxide to enhance the performance for the sensitive and selective detection of toluene. The response of toluene sensor in the detection range 10–1000 ppm was examined. [ABSTRACT FROM AUTHOR]

ZnO nanowires were grown on the active sensor surface of a surface acoustic wave (SAW) sensor via a vapour–liquid–solid (VLS) technique using pulsed laser deposition (PLD) as the particle source. The fabricated sensors were “delay-line” type (quartz substrate; ∼69.4-MHz central frequency). The nanowire length and diameter were controlled by the growth time and temperature, respectively. The sensor response at room temperature to various hydrogen (H 2 ) concentrations was recorded for different ZnO morphologies and nanowire thicknesses and compared with the performance of a thin-film sensor with a comparable amount of ZnO material. The sensor response depended on the ZnO volume and the morphology of the active surface. An increase in the ZnO volume enhanced the frequency shift for the same H 2 concentration, while the larger surface area of the longer nanowires enhanced the sensor response to low H 2 concentrations, enabling detection of concentrations as low as 0.01%. [ABSTRACT FROM AUTHOR]

Thin films of indium tin oxide were grown by the direct evaporation technique. The sensors fabricated under the optimized deposition conditions were exposed at room temperature (303 K) to different concentrations of formaldehyde vapours and the relative change in resistance was measured. The effect of the film thickness on the response to test vapours was studied. In order to enhance the sensitivity, sensors with thin promoting layers of different metals and oxide like Cu, Ag and MgO deposited on the top of the film were fabricated and tested. The sensors with improved sensitivity were studied for the elaborate response to formaldehyde vapours at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: The development of reliable hydrogen sensors will facilitate the introduction of hydrogen to the natural gas infrastructure. One of the most promising configurations for such a device is a thin film based fiber optic sensor. We demonstrate that with such a device not only the measurement of a specific threshold partial pressure is possible, but also allows for a quantitative determination of the partial hydrogen pressure measured real-time and in-situ in the gas stream. The changing hydrogen pressure, up to 200mbar partial pressure, can be measured optically using a Pd–Au alloy thin film. However for the daily use of the sensor in the natural gas infrastructure it is important to determine the hydrogen sensing abilities under non-ideal conditions i.e. in gas mixtures containing high concentrations of CH4, C2H6, and C3H8. It is found that, the type of carrier gas (i.e. Ar (clean-conditions), CH4, C2H6, and C3H8) has hardly any influence on the measured hydrogen concentration and switching kinetics of the sensor. The sensor response times (hydrogenation kinetics) are comparable to those for clean H2 flows. [Copyright &y& Elsevier]

Abstract: A contactless smart card with integral wireless power and data link and on-board chemical sensor is described. The chemical sensor part of the smart card comprises a planar conductometric interface onto which a chemically or biologically sensitive thin film may be cast using microfabrication techniques. The thin film sensor and conductometric interface form an integral part of a radio-frequency smart card that has been designed for use in distributed chemical and biological detection systems, and which is based upon the International Standards Organisation high-frequency (HF) ISO 15693 radio-frequency identification (RFID) protocol. Conductometric measurements are controlled, sampled and stored by the smart card electronics. Measurement results achieved with an organic semiconductor, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), PEDOT-PSS, as a model thin film conductometric sensor material cast on planar gold electrodes are reported. The standardisation of short-range wireless radio protocols such as Bluetooth, RuBee, ZigBee, WiFi and RFID is opening new markets for distributed sensors and sensor networks, and the fusion of chemical and biosensor technologies with short-range, low-cost, wireless technologies will create new opportunities for chemical and biological sensor systems in healthcare, environmental monitoring, process and quality control, and chemical and biological threat detection. The chemical sensor smart card described here could in future be suitable for use in various distributed short range wireless data applications and sensor networks as part of the emerging sensor Internet of Things. [Copyright &y& Elsevier]

Highlights: [•] Primary amine modified polyaniline nanothin film chemiresistor sensor for formaldehyde. [•] Nucleophilic addition of amines with formaldehyde carbonyl reaction. [•] Limit of detection 400ppb, ∼half of permissible exposure level. [•] Selectivity against acetaldehyde, acetone and formic acid. [ABSTRACT FROM AUTHOR]

Thin film sensors on the basis of evaporated layers of chalcogenide glasses for heavy metal ions are developed. In spite of the promising results and good electrochemical performance, the long-term stability of chalcogenide-based thin film sensors is still a problem. In this paper, AES study was made to clarify the problem with “the aging” of chalcogenide thin film membranes.The electrochemical performance of chalcogenide glass membranes covered with plasma deposited polymer film of polyhexamethyldisiloxane (PHMDSO) and vacuum deposited polyimide (PI) was investigated. It was established that both polymer layers improve the electrochemical characteristics of the membranes—increase the sensitivity, the detection limits and long-term stability while maintaining a stable response time and very good reproducibility. [Copyright &y& Elsevier]

A thin film semiconductor sensor array has been employed to discriminate several aromatic compounds in water, ethanol and wine. These compounds are aromas or off-odours usually found in wines: acetic acid, ethyl acetate, acetaldehyde, trichloroanisole (TCA) and SO2. The concentrations of these compounds were in the range of mg/l except in the case of TCA that was in the ng/l range. Principal component analysis (PCA) and radial basis neural networks (RB-NN) were performed in the data. The results showed that despite the strong influence of ethanol the system could discriminate correctly the compounds. [Copyright &y& Elsevier]

Data is presented from a comparison of Stern–Volmer studies on oxygen quenching of Pt octaethylporphyrin (PtOEP) luminescence both in fluid solution and encapsulated in ethylcellulose (EC) polymer films, and for PdOEP luminescence in EC, using three different experimental methods: time-resolved nanosecond laser kinetics, true steady-state luminescence, and gated luminescence using a 10 μs pulsed xenon lamp excitation source. While the first two methods give results that are reliable and in good agreement, results obtained using pulsed xenon lamp excitation with emission gating are unreliable because of systematic errors in quantitative emission intensity measurements using this type of apparatus. The sources and effects of these errors are identified and discussed. [Copyright &y& Elsevier]