Portable ppb-level SO2 gas sensor based on CeO2 solid electrolyte

Acetone is one of the most abundant volatile compounds in the human breath and might be important for monitoring diabetic patients. Here, a portable acetone sensor consisting of flame-made, nanostructured, Si-doped WO3 sensing films was used to analyse the end tidal fraction of the breath (collected in Tedlar bags) from eight healthy volunteers after overnight fasting (morning) and after lunch (afternoon). After breath sampling, the gaseous components were also analysed by proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS), and each person's blood glucose level was measured. The portable sensor accurately detected the presence of acetone with fast response/recovery times (<12 s) and a high signal-to-noise ratio. Statistical analysis of the relationship between the PTR-TOF-MS measurements of breath gases (e.g., acetone, isoprene, ethanol and methanol), sensor response and the blood glucose level was performed for both sampling periods. The best correlations were found after overnight fasting (morning): in particular, between blood glucose level and breath acetone (Pearson's 0.98 and Spearman's 0.93). Whereas the portable sensor response correlated best with the blood glucose (Pearson's 0.96 and Spearman's 0.81) and breath acetone (Pearson's 0.92 and Spearman's 0.69).

During the last few years, interest in wearable devices including a portable and wearable gas sensor system has increased. Since integration of fabric and gas sensors for a wearable breath monitoring system would allow continuous monitoring patients’ breathing gases such as acetone gas for diabetes (1), ammonia for renal disease (2), and ethanol for hepatic steatosis (3), realization of a miniaturized wearable gas sensor operating at daily environment is in demand. Zinc oxide has definite advantages over other semiconducting nano-scale metal oxides because of its electric properties such as wide bandgap and high electron mobility (4). ZnO nanostructures have been investigated such as nanorods, nanotubes, and nanowires. Recently, hollow micro/nanosphere ZnO has been attracting attention. It may be able to apply for dye-sensitized solar cells, photocatalts, high performance electrodes, and gas sensors due to its large surface-to-volume ratio and reduced transport lengths for both mass and charge transport (5). The researches about the catalytic decoration of ZnO gas sensors by metallic nanoparticles or layers have been also investigated to improve selectivity (6, 7). Especially, ZnO with silver is considered to exhibit relatively high sensitivity to ethanol (7). In this study, the hollow microsphere ZnO particles were prepared by a simple but new precipitation method and then Ag sputter coated. Electrophoretic deposition (EPD) of the hollow particles with Ag was then used to construct ZnO-Ag layers on flexible polyimide films. The structural properties of the deposited ZnO layers were analyzed by using SEM, TEM, and XRD. Then, gas sensing behaviors to detect ethanol, acetone, and ammonia by thickness of Ag are discussed in detail. This research was partially supported by the Korea Institute of Energy Technology Evaluation and Planning (20158520000210) grant funded by the Korea Government Ministry of Trade, Industry and Energy, a grant from a Strategic Research Project (2013-0132) funded by the Korea Institute of Construction Technology, and Auburn University IGP. (1) Zhang, Q., Wang, P., Li, J., and Gao, X. (2000) Biosens. Bioelectron. 15, 249-256 (2) Moorhead, K. T., Lee, D., Chase, J. G., Moot, A., Ledingham, K., Scotter, J., Allardyce, R., Senthilmohan, S., and Endre, Z. (2008) Computer methods and programs in biomedicine 89, 226-238 (3) de Lacy Costello, B., Ewen, R., Ratcliffe, N. M., and Richards, M. (2008) J. Breath Res. 2, 037017 (4) Ahn, H., Park, J.-H., Kim, S.-B., Jee, S. H., Yoon, Y. S., and Kim, D.-J. (2010) Electrochemical and Solid-State Letters 13, J125-J128 (5) Xie, Q., Li, J., Tian, Q., and Shi, R. (2012) Journal of Materials Chemistry 22, 13541-13547 (6) Lupan, O., Chow, L., Ono, L. K. Ono, Cuenya, B. R., Chai, G., Khallaf, H., Park, S., and Schulte, A. (2010) The Journal of Physical Chemistry C 114, 12401-12408 (7) Lyashkov, A. Yu, Tonkoshkur, A. S., Aguilar-Martinez, J. A. and Glot, A. B. (2013) Ceramics International 39, 2323-2330

Owing to the unique properties such as pristine interfaces, ultra‐thin and uniform thickness, 2D nanomaterials have attracted the attention from many researchers. Particularly, rGO and MXene 2D nanomaterials have received intense research interest in the application of gas sensors due to their high electrical conductivity. The coating of these 2D nanomaterials onto plastic, paper or textile substrate formed flexible, stretchable and portable gas sensors as an alternative to the conventional rigid gas sensors. To date, numerous research works on flexible gas sensors using either graphene or MXene have been published. However, the reported data is scattered and varied by multiple factors. In this short review, we revisit the advances in the current application of 2D conductive nanomaterials (mainly rGO and MXene) and their nanocomposites with metal oxides on flexible gas sensors. We focus on recent developments regarding the working mechanism, advantages, disadvantages, and performances (including gas response, selectivity, response time, and recovery time) of each type of gas sensor. Finally, this short review sheds light on future directions and prospects in the field of flexible gas sensors using 2D nanomaterials.

Hydrogen sulfide is found in many environments including sewage systems, petroleum extraction platforms, kraft paper mills, and exhaled breath, but its determination at ppb levels remains a challenge within the analytical chemistry field. Off-line methods for analysis of gaseous reduced sulfur compounds can suffer from a variety of biases associated with high reactivity, sorptive losses, and atmospheric oxidative reactions. Here, we present a portable, online, and disposable gas sensor platform for the in situ determination of gaseous hydrogen sulfide, employing a 470 nm light emitting diode (LED) and a microfiber optic USB spectrometer. A sensing layer was created by impregnating 2.5 μL (0.285 nmol) of fluorescein mercury acetate (FMA) onto the surface of a micropaper analytical device with dimensions of 5 × 5 mm, which was then positioned in the optical detection system. The quantitative determination of H2S was based on the quenching of fluorescence intensity after direct selective reaction between the gas and FMA. This approach enabled linear calibration within the range 17-67 ppb of H2S, with a limit of detection of 3 ppb. The response time of the sensor was within 60 s, and the repeatability was 6.5% (RSD). The sensor was employed to monitor H2S released from a mini-scale wastewater treatment tank in a research laboratory. The appropriate integration of optoelectronic and mechanical devices, including LED, photodiode, pumps, and electronic boards, can be used to produce simple, fully automated portable sensors for the in situ determination of H2S in a variety of environments.

Simple, accurate, portable, and selective gas sensors with autonomous, remote, and real-time access have become a requisite in various fields of applications. In this article, we report the development of a stand-alone and selective gas sensor system incorporating a single resistive sensor with wireless monitoring and Internet connectivity. The sensor is fabricated in-house with platinum-decorated tin-oxide hollow spheres as the sensing material, which exhibits a prominent response toward the tested volatile organic compounds (VOCs) at different concentrations. The intelligence in terms of accurate identification of VOCs and their concentration is attained by employing a machine learning tool based on a deep neural network. The applied model displays an average accuracy of 96.43% with a fast prediction speed of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$310~\mu \text{s}$ </tex-math></inline-formula> , allowing a real-time recognition capability. The wireless connectivity is established utilizing a low-power microcontroller board and a Bluetooth module. The real-time data is made available for the users over an Android-based mobile application and a webpage while utilizing cloud services through the Internet. The implemented system is successfully experimented with and validated under different test conditions that verify the whole platform. Further, the sensor system can be potentially applied to a remote application without needing any manual involvement. The demonstrated work with an Internet of Things (IoT) paradigm strengthens the next-generation gas sensing technology for developing smart, selective, and real-time gas sensor systems.

Modeling of gaseous pollutants (CO and NO2) emission from an industrial stack in Kano city, northwestern Nigeria

Global air quality has deteriorated significantly in recent years due to large emissions from the transformation industry and combustion vehicles. This issue requires the development of portable, highly sensitive, and selective gas sensors. Nanostructured materials, including defective graphene, have emerged as promising candidates for such applications. In this work, we investigated the B-doped topological line defect in graphene as a sensing material for various gas molecules (CO, CO2, NO, and NH3) based on a combination of density functional theory and the non-equilibrium Green's function method. The electronic transport calculations reveal that the electric current can be confined to the line defect region by gate voltage control, revealing highly reactive sites. The B-doped topological line defect is metallic, favoring the adsorption of NO and NH3 over CO and CO2 molecules. We notice changes in the conductance after gas molecule adsorption, producing a sensitivity of 50% (16%) for NO (NH3). In addition, the recovery time for nitride gases was calculated for different temperatures and radiation frequencies. At 300 K the ultraviolet (UV) has a fast recovery time compared to the visible (VIS) one by about two orders of magnitude. This study gives an understanding of how engineering transport properties at the microscopic level (by topological line defect and chemical B-doping) leads to promising nanosensors for detecting nitride gas.

We demonstrated in this work the usefulness of solvate ionic liquids SIL 3 and SIL 4 for chemoselective detection of amine gases on a quartz crystal microbalance. This detection of gaseous amines was achieved by nucleophilic aromatic addition reactions with super electrophilic SIL 3 or SIL 4 thin-coated on quartz chips. Starting with inexpensive reagents, functional SIL 3 and SIL 4 could be readily synthesized in two short steps with high isolated yield (81 and 77%, respectively). The QCM platform developed in this work is readily applicable and highly sensitive to low molecular weight amine gases: for propylamine gas at 10 Hz decrease in resonance frequency, the sensitivity of detection using SIL 4 was 5.4 ppb. This simple and convenient assembly of neutral ligands (e.g., 1a and 1b) with Li+ ion to afford room temperature ionic liquids should be of great importance for a myriad of applications. To the best of our knowledge, no example to date of reports based on nucleophilic aromatic addition reactions demonstrating sensitive amine gas detection in solvate ionic liquids on a QCM has been reported. Furthermore, because of the high color intensity of the Meisenheimer complexes formed, our preliminary result showed that SIL 4 loaded on copier paper can be used not only as a portable amine gas sensor but also as a potential invisible ink that is only revealed by amine vapor.

Graphene-based fibers (GFs) have aroused enormous interest in portable, wearable electronics because of their excellent mechanical flexibility, electrical conductivity, and weavability, which make them advantageous for wearable electronic devices. Herein, we report the development of metal binder-free Ti3C2Tx MXene/graphene hybrid fibers by a scalable wet-spinning process. These hybrid fibers exhibit excellent mechanical and electrical properties for applications in flexible wearable gas sensors. The synergistic effects of electronic properties and gas-adsorption capabilities of MXene/graphene allow the created fibers to show high NH3 gas sensitivity at room temperature. The hybrid fibers exhibited significantly improved NH3 sensing response (ΔR/R0 = 6.77%) compared with individual MXene and graphene. The hybrid fibers also showed excellent mechanical flexibility with a minimal fluctuation of resistance of ±0.2% and low noise resistance even after bending over 2000 cycles, enabling gas sensing during deformation. Furthermore, flexible MXene/graphene hybrid fibers were woven into a lab coat, demonstrating their high potential for wearable devices. We envisage that these exciting features of 2D hybrid materials will provide a novel pathway for designing next-generation portable wearable gas sensors.

A portable, low-power, battery operated hydrogen detection system has been developed and built. Significant performance advantage is achieved using Sandia National Laboratories' robust, wide range hydrogen sensor technology. Features of the prototype system include dual set points with audible and flashing LCD alarms as well as direct readout in ppm of hydrogen gas concentration.

We demonstrate the results of numerical simulations of 1.3μm InAlGaAs/InP VCSEL with a ring pattern etched at the interface between the cavity and top DBR. We show that the proposed design offers selective confinement of the fundamental mode and strong discrimination of higher order modes. Consequently, VCSEL with ring confinement is capable to operate in a broad range of injected currents in the single mode regime, which facilitates the improvement of maximal emitted power and increase of the wavelength tuning range with very narrow spectral characteristics. High power, single-mode emitting vertical-cavity surface-emitting lasers (VCSELs) are of great interest, since they can serve as high-power, smoothly tuned with current and temperature, coherent-optical sources. Emerging applications include inexpensive and portable gas sensors, telecommunication emitters, and so on. For these applications, it is preferable to have a low-threshold, high side-mode suppression ratio (SMSR) light source. VCSELs inherently emit in a single longitudinal mode; controlling the lateral mode is far more complicated. It can be achieved using a well-established wet oxidation technology, which makes possible single-mode operation only for relatively narrow apertures (providing less than 5 mW of output power) (1). Other methods provide up to twofold higher emitted power but exploit more challenging technologies (2-5). The limitation of high power single mode operation comes from small optical apertures or multimode operation under high injection levels. This paper provides numerical analysis of the ring pattern etched in the cavity of the VCSEL which eliminates higher order mode emission. The ring pattern provides confinement for a fundamental mode and forces higher order modes to be pushed out of the active region. The analyzed structure (Fig. 1a) (6) incorporates InAlGaAs quantum wells within an InP cavity. The cavity is bounded by 35 pairs of Al0.9Ga0.1As/GaAs DBRs from the bottom and 20.5 pairs of Al0.9Ga0.1As/GaAs DBRs from the top. Laterally patterned tunnel junction (TJ) layers are responsible for tunnelling carriers into the

Several molecules of interest have their absorption signature in the mid-infrared. Spectroscopy is commonly used for the detection of these molecules, especially in the short-wave infrared (SWIR) region due to the low water absorption. Conventional spectroscopic systems consist of a broadband source, detector and dispersive components, making them bulky and difficult to handle. Such systems cannot be used in applications where small footprint and low power consumption is critical, such as portable gas sensors and implantable blood glucose monitors. Silicon-On-Insulator (SOI) offers a compact, low-cost photonic integrated circuit platform realized using CMOS fabrication technology. On the other hand, the GaSb material system allows the realization of high performance SWIR lasers and detectors. Integration of GaSb active components on SOI could therefore result in a compact and low power consumption integrated spectroscopic system. In this paper, we report the study on thin-film GaSb Fabry-Perot lasers integrated on a carrier substrate. The integration is achieved by using an adhesive polymer (DVS-BCB) as the bonding agent. The lasers operate at room temperature at 2.02μm. We obtain a minimum threshold current of 48.9mA in the continuous wave regime and 27.7mA in pulsed regime. This yields a threshold current density of 680A/cm² and 385A/cm², respectively. The thermal behaviour of the device is also studied. The lasers operate up to 35 &deg;C, due to a 323 K/W thermal resistance

Surface Modification of Acrylic Fiber by Polyaniline-ZnO Nanocomposite and Its Application as a Portable Gas Sensor

Effect of oxygen-containing groups in functionalized graphene on its gas sensing properties

Low-power, and relatively low-cost, gas sensors have potential to improve understanding of intra-urban air pollution variation by enabling data capture over wider networks than is possible with ‘traditional’ reference analysers. We evaluated an Aeroqual Ltd. Series 500 semiconducting metal oxide O3 and an electrochemical NO2 sensor against UK national network reference analysers for more than 2 months at an urban background site in central Edinburgh. Hourly-average Aeroqual O3 sensor observations were highly correlated (R2 = 0.91) and of similar magnitude to observations from the UV-absorption reference O3 analyser. The Aeroqual NO2 sensor observations correlated poorly with the reference chemiluminescence NO2 analyser (R2 = 0.02), but the deviations between Aeroqual and reference analyser values ([NO2]Aeroq − [NO2]ref) were highly significantly correlated with concurrent Aeroqual O3 sensor observations [O3]Aeroq. This permitted effective linear calibration of the [NO2]Aeroq data, evaluated using ‘hold out’ subsets of the data (R2 ≥ 0.85). These field observations under temperate environmental conditions suggest that the Aeroqual Series 500 NO2 and O3 monitors have good potential to be useful ambient air monitoring instruments in urban environments provided that the O3 and NO2 gas sensors are calibrated against reference analysers and deployed in parallel.