High-sensitivity Gas Research Articles

Simultaneous Determination of 7 Short-Chain Fatty Acids in Human Saliva by High-Sensitivity Gas Chromatography-Mass Spectrometry

Simultaneous Determination of 7 Short-Chain Fatty Acids in Human Saliva by High-Sensitivity Gas Chromatography-Mass Spectrometry

Enrichment of Semiconducting Single-Walled Carbon Nanotubes with Indigo-Fluorene-Based Copolymers and Their Use in Printed Thin-Film Transistors and Carbon Dioxide Gas Sensors.

High-purity semiconducting single-walled carbon nanotubes (sc-SWCNTs) are promising for portable and high-sensitivity gas sensors because of their excellent physical and electrical properties. Here, we describe the synthesis of a novel indigo-fluorene-based copolymer (PFIDBoc) that has been designed to selectively enrich sc-SWCNTs with excellent purity (>99.9%) yet contain a latent function in the form of a tert-butoxy (t-BOC)-protected amine that can be later revealed and exploited for carbon dioxide (CO2) gas sensing. SWCNTs wrapped with the PFIDBoc polymer can be easily converted via an on-chip thermal process to reveal a vinylogous amide moiety with a secondary amine nitrogen within the indigo building block of the copolymer which is perfectly suited for CO2 recognition. Thin-film transistors and sensors were inkjet-printed onto rigid and flexible substrates, demonstrating the versatility of enriched PFIDBoc-derived sc-SWCNT dispersions. The printed transistors exhibited a mobility up to 9 cm2 V-1 s-1 and on/off current ratios >105. We further demonstrate herein a CO2 sensor for indoor air quality monitoring even in low humidity environments, possessing a linear response with up to ∼5.4% sensitivity and a dynamic range between 400 and 2000 ppm in air with a relative humidity of ∼ 40%.

Focus of mineralization-synthesis processes of the organic matter in the leached chernozem while cultivating potatoes on different fertilization backgrounds

Aim. To investigate the focus of the mineralization–synthesis processes in leached chernozem while cultivating potatoes in different fertilization systems, ensuring different supplies of raw organic matter into the soil. Methods. Field experiment, gas chromatography. Results. The study of emissions of nitrous oxide and carbon dioxide from the soil followed by the calculations of the specifi c losses of N-N2O (g/kg C-CO2), depending on fertilization system and in comparison with the indicators of the “reference” soil, provide an opportunity for rapid determination of the focus of the mineralization-synthesis processes in the organic matter in agrocenoses. The use of exclusively mineral fertilization systems results in the highest specifi c losses of N2O as the increase of the applied fertilizer doses initiates the mineralization processes in the soil. The combination of mineral fertilizers with raw organic products (5 t/ha straw and 13 t/ha of lupine cover crop) signifi cantly improves the situation. At the same time, in experiment with the lowest (N40P40K40 kg/ha) and medium (N80Р80К80 kg/ha) doses of mineral fertilizers the balance of mineralization-synthesis processes of organic matter was observed. The highest rate of mineral fertilizer dose in the experiment (N120P120K120 kg/ha), even in combination with the raw organic material, activates mineralization processes. With the use of manure, as well as upon its combination with the lupine cover crop and low doses of mineral fertilizers, the optimization of nitrous oxide and carbon dioxide emissions is observed. Conclusions. The use of solely mineral fertilizers in the technology of potato cultivation is inappropriate in terms of environmental reasons. The combination of mineral fertilizers (not exceeding N80Р80К80 kg/ha dose) with straw and lupine cover crop ensures optimization of the processes of mineralization-synthesis of organic matter. Moreover, the optimization of biological processes in the soil was observed in experiments with the use of manure, its combination with lupine cover crop and low doses of mineral fertilizers. The calculations of the indices of mineralization-synthesis of organic matter, considering the emission factors of N2O and CO2, obtained with the use of modern high-sensitivity gas chromatographic methods, allow to determine the focus of biological processes in the soil, depending on fertilization system, and to estimate ecologic sustainability of types and doses of fertilizers.

Study of Polyoxometalates Based Films Formation with High Gas Sensitivity

Introduction Inorganic oxide films activated with different additives are the unique sensitive layers for working at room temperature sensors. The sensor behavior of nanostructured activated silica films produced by sol-gel route was examined for environment control. Polyoxometalates (POMs) of Dawson type were used as additives in the silica matrix for gas sensitivity. POMs have good electronic conductivity and chemical stability. These compounds can act as reversible reagents in the reactions of ligand exchange and redox transformations, accompanied by changes in current carrier concentration or catalyze of such transformations that can be used in chemical sensors. Their redox properties can be varied within broad limits due to changing the heteropolyanion composition [1-4]. Porous silica is a unique matrix for chemical sensors, which has a lot of excellent physical and chemical properties [5]. Method The sensor’s interdigital structure was made by microelectronic planar technology as shown in figure 1. The active area of the sensor was 4 x 4 mm. The thickness of the electrodes was 0,2 mm. The width of finger pairs of electrodes and distance between them were 20 μm. The method of hydrolythic polycondensation from tetraethyl orthosilicate solutions was used for forming complex silica films in this work. Films were deposited by a centrifugation from solutions based on tetraethyl orthosilicate and polyoxometalate. POMs with various compositions have been incorporated into the initial solution. The developed technology of multistep temperature treatment up to 413 K allowed film properties stabilizing.The conditions of film formation varied during the tests: solution composition, temperature, and application modes. Morphology and infrared spectra of the layers were studied using Solver-P47 scanning probe microscope (NT-MDT, Russia) and spectrometer Bruker EQUINOX 55 (Germany). Standard gas mixtures (MGPZ, Russia) and Environics – 4000 gas-mixture generator (Environics, USA) were used to measure the properties of sensors. Electrical parameters of the sensors have been measured in real-time mode. Environment influence on sol preparation and films forming was investigated. Results and Conclusions Films had thickness of 200-300 nm and nanoscale pores. The metrological parameters of sensors depend mainly on different parameters: synthesis conditions and chemical content of sensitive film, temperature of the environment, annealing temperature, storage conditions and duration after heat treatment. Temperature treatment and decreasing of environment humidity lead to acceleration of hydrolythic polycondensation of solutions and stabilization of sensitive films at right conditions as demonstrated in figure 2. Introduction of heteropolyanion into film resulted in film’s mass stabilization. The temperature treatment don’t disturb POM molecule in the film. The polyoxometalates didn’t display their catalytic activity at weight content less than 10 % in the film. The increase in conductivity is observed due to an increase in the concentration of charge carriers on the surface of the film, donors of which are introduced into the film POM molecules. And gas sensitivity maximum decreases at weight content more than 50-60 % in matrix what is explained apparently by the formation of crystalline aggregates POM in the volume of the film. Besides the humidity adsorption on the film’s surface contribute to the sensor response. Adding of Mn3P2Mo18O62 into silica film resulted in high sensitivity to ethanolamine (up to 10 times) more than to ammonia as shown in figure 3. Obviously, this is explained by the reaction of ethanolamine complexation with Mn ions, among the possible valence states of which the strongest complex with ethanolamine molecules is formed by Mn3+. An equilibrium shift towards Mn3+ and a decrease in the redox potential of the Mn3+/Mn2+ pair leads to an intramolecular reduction reaction of the heteropolyanion. This interaction is quick (less than 30 s) and reversible at room temperature.

Heterostructural Nano-Scale Conductometric Sensing Devices to Improve Selective Gas Detection

Heterostructural Nano-Scale Conductometric Sensing Devices to Improve Selective Gas Detection

Flexible Screen-Printed CNT Electrode on Porous PTFE Substrate with Gold Nanoparticle Modification for Rapid Electrochemical Gas Sensing

Flexible Screen-Printed CNT Electrode on Porous PTFE Substrate with Gold Nanoparticle Modification for Rapid Electrochemical Gas Sensing

Fabrication of electrospun Co3O4/CuO p-p heterojunctions nanotubes functionalized with HFIP for detecting chemical nerve agent under visible light irradiation

Organic functionalized composite metal oxide nanomaterials are promising for reliable selective and high sensitive gas sensors based on their chemical bonding with the targeted molecules and rapid transport pathways of charges. The selectivity of semiconducting metal oxides (SMOs) still insufficient and its mechanism is not clearly demonstrated, which restricts their application. Herein, hexafluoroisopropanol (HFIP) groups were grafted on the composite Co3O4/CuO nanotubes as a hybrid sensing material for detecting dimethyl methylphosphonate (DMMP), sarin nerve agent simulant. Porous composite Co3O4/CuO nanotubes were fabricated via electrospun of a polymeric blend as a sacrificial template to construct nanotubes (NTs) based on the phase separation property. The designed hybrid HFIP-Co3O4/CuO NTs showed high response (8.8 Rg/Ra at 90 °C), rapid response (7.3 s)-recovery (5.2 s) times and excellent selectivity to 0.5 ppm DMMP under light irradiation compared to un-functionalized sample and the response in dark, indicating to the specific bonding between HFIP and DMMP via hydrogen bonds and photo-generation of charge carriers. The hybrid sample showed high reversibility and humidity independence under light, approving the repeatability of the chemisorption processes and the hydrophobic behavior of HFIP groups. The enhanced DMMP detection is attributed to the photoactivation of p-p heterojunctions Co3O4/CuO NTs and HFIP functionalization.

HFIP-functionalized electrospun WO3 hollow nanofibers/rGO as an efficient double layer sensing material for dimethyl methylphosphonate gas under UV-Light irradiation

Abstract Gas sensing materials-based transition metal oxides have insufficient sensing properties that limit their application. Inorganic-organic hybrid nanomaterials are the most advanced materials for high sensitivity gas sensors. Herein, hexafluoroisopropanol (HFIP) was grafted on the tungsten trioxide (WO3) hollow nanofibers (HNFs) for detecting dimethyl methylphosphonate (DMMP, sarin agent simulant) due to the hydrogen bonding. Furthermore, reduced Graphene Oxide (rGO) nanosheets were applied as a base layer to avoid the grain boundaries poisoning and enhance the charge mobility. As well, the UV-light photoactivation of the sensing materials was investigated. The double layer rGO/WO3–HFIP exhibited high and rapid responses toward DMMP in comparison with WO3 HNFs and double layer rGO/WO3 after the exposure to various gases. The sensing performance of all sensors improved under UV-light irradiation, demonstrating the UV-light activation of their sensing properties. The double layer rGO/WO3–HFIP showed a high response (17.6) at 150 °C of 10 ppm DMMP with maintaining 90% of it at a relative humidity (80 RH %). In addition to a low detection limit of 0.1 ppm DMMP, indicating the role of HFIP as a hinter of DMMP molecules. This work provides an efficient synthetic method of double layer rGO/WO3–HFIP sensing material for DMMP detection.

Improved Hydrogen Sensing Performance of AlGaN/GaN Based Gas Sensors with Controlled Surface Nanostructures of Platinum Nanoparticulate Films.

A simple and convenient method for the formation of Pt nanoparticulate films as a sensing material by controlling deposition rates is demonstrated to realize AlGaN/GaN high electron mobility transistor-based high-sensitivity hydrogen gas sensors. The Pt nanoparticulate films produced at a low deposition rate (Sample 1: 0.3 Å/s) exhibit a smooth surface and uniformly sized Pt grains, while the films produced at a high deposition rate (Sample 2: 1.5 Å/s) consist of bigger Pt grains and more coalesced grains on the surface. The deposition rate has a distinct effect on the surface morphology. The maximum current change percentage for sample 1 is 2.1×10³% at a VGS of -4.3 V while that for sample 2 is 4.4×10³% at a VGS of -4.5 V. Sample 2 has a two times larger current response to hydrogen gas than sample 1, which results from a large increase in channel conduction induced by a huge catalytic surface area of Pt nanoparticulate films. This technique offers an alternative method for the facile deposition of a sensing material and is potentially useful in various applications, such as gas, chemical, and biological sensors.

Highly sensitive optical waveguide sensor for SO2 and H2S detection in the parts-per-trillion regime using tetraaminophenyl porphyrin

ABSTRACTOptical waveguide (OWG) sensors present great potential for detecting trace levels of harmful gases because of their high sensitivity and anti-electromagnetic interference. However, OWG-based SO2 and H2S-detecting sensors in the parts-per-trillion (ppt) range are still lacking. We fabricated 5,10,15,20-(tetra-4-aminophenyl) porphyrin (TAPP) thin film-based OWG sensor devices (TAPP-OWG) to detect SO2 and H2S gases, in which TAPP thin film was immobilized over the surface of a potassium ion exchange glass OWG. These sensors successfully measure extremely low concentrations of SO2 and H2S (detection limit = 1 ppt), providing good repeatability for SO2 (10 ppt) and H2S (10 ppt) gases, with relative standard deviations of 1.67% and 3.68%, respectively. With fast response (t1) and recovery (t2) times for SO2 (t1=4 s, t2=157 s) and H2S (t1=2 s, t2=117 s) at room temperature, TAPP thin film enhances the potential of OWGs for use in high-sensitivity trace-level gas detection.

Effect of Mixing Ratio of (SnO2)1-x(In2O3)x Thin Film on Gas Sensitivity

In this work, Nitrogen dioxide gas sensorwas manufactured from SnO2 and (SnO2)1-x(In2O3)x at different atomic ratios (x=0.05, 0.1 and 0.15) using pulsed laser deposition technique. The effect of the preparation ratio on structural properties, surface topography, optical and electrical characteristics and gas sensor efficiency were studied. The x-ray diffraction measurements showed polycrystalline structures for all samples and their crystallite size decreases with increasing the doping ratio. The AFM measurement illustrates spherical SnO2 shapes converted to filament-like shapes at x=0.1, and that the average particle diameter decreased, while the RMS roughness increased with increasing ratio. The best samples in terms of gas sensitivity were produced at the 0.1 ratio due to the associated with low particle sizes and high charge carrier concentration. The highest gas sensitivity appeared at 200 °C operating temperature, and it is increased with gas concentration as a second-order equation and be nearly stable at 400 ppm NO2 gas. The best sample appeared at 10% In2O3:SnO2atomic ratio.

A rapid, spatially dispersive frequency comb spectrograph aimed at gas phase chemical reaction kinetics

This New Views article will highlight some recent advances in high sensitivity gas detection using direct infrared absorption frequency comb laser spectroscopy, with a focus on frequency comb use in chemical reaction kinetics and our own contribution to this field. Our recently implemented detection technique uses a combination of a 12.9 GHz free spectral range virtually imaged phased array and diffraction grating to spatially disperse the mid-infrared frequency comb onto a camera. Individual frequencies or ‘comb teeth’ of a 250 MHz repetition-rate frequency comb are able to be resolved. High molecular sensitivity is achieved by increasing the interaction path length using a Herriott multipass cell. High spectral resolution, broadband spectral coverage, and high molecular sensitivity are all achieved on an adjustable 1–50 µs timescale, making this frequency comb apparatus ideal for measuring chemical reaction kinetics where multiple absorbing species can be monitored simultaneously. This New Views article will also discuss some of the challenges and decisions that chemists might face in implementing this advanced physics technology in their own laboratory. Spatially dispersed 250 MHz mid-infrared frequency comb laser, with absorption of some frequencies by a dilute sample of methane.

High-sensitivity photoacoustic gas detector by employing multi-pass cell and fiber-optic microphone.

A high-sensitivity photoacoustic (PA) spectroscopy (PAS) system is proposed for dual enhancement from both PA signal excitation and detection by employing a miniaturized Herriott cell and a fiber-optic microphone (FOM). The length of the optical absorption path of the PA cell is optimized to ∼374 mm with 17 reflections. The volume of the PA cell is only 622 µL. The FOM is a low-finesse fiber-optic Fabry-Pérot (FP) interferometer. The two reflectors of the FP cavity are formed by a fiber endface and a circular titanium diaphragm with a radius of 4.5 mm and a thickness of 3 µm. A fast demodulated white-light interferometer (WLI) is utilized to measure the absolute FP cavity length. The acoustic responsivity of the FOM reaches 126.6 nm/Pa. Several representative PA signals of trace acetylene (C2H2) are detected to evaluate the performance of the trace gas detector in the near-infrared region. Experimental results show that the minimum detectable pressure (MDP) of the FOM is 3.8 µPa/Hz1/2 at 110 Hz. The noise equivalent minimum detection concentration is measured to be 8.4 ppb with an integration time of 100 s. The normalized noise equivalent absorption (NNEA) coefficient is calculated as 1.4×10-9 cm-1·W·Hz-1/2.

Serum Copeptin Levels Predict the Return of Spontaneous Circulation and the Short-Term Prognosis of Patients with Out-of-Hospital Cardiac Arrest: A Randomized Control Study.

Early and accurate prediction of survival to hospital discharge following resuscitation after cardiac arrest (CA) is a major challenge. Biomarkers can be used for early and accurate prediction of survival and prognosis following resuscitation after CA, but none of those identified so far are sufficient by themselves. The goal of this study was to investigate the predictive power of the serum copeptin level for determining the return of spontaneous circulation (ROSC) and prognosis of patients with non-traumatic out-of-hospital cardiac arrest (OHCA) who underwent cardiopulmonary resuscitation (CPR). A total of 76 consecutive consenting adult patients who were diagnosed as non-traumatic OHCA and 63 age- and sex-matched healthy controls were enrolled. The patients were divided into two groups based on whether or not they had ROSC. The ROSC group was divided into two sub-groups according to whether death occurred within 24 hours or after 24 hours following ROSC. Serum copeptin, high-sensitivity cardiac troponin (hs-cTnI), creatine kinase-muscle/brain (CK-MB), glucose, and blood gas values were compared between the groups. Serum copeptin levels were significantly higher in the patient group than control group (P <.001). Receiving operator characteristic analysis revealed a cut-off copeptin level of 27.29pmol/L, with 98.7% sensitivity and 100.0% specificity, for distinguishing patients from controls. Serum copeptin levels were significantly lower in the ROSC group than non-ROSC group (P = .018). Additionally, the mean serum hs-cTnI level was significantly higher in the ROSC group than non-ROSC group (P = .032). However, there were no significant differences in the mean serum glucose level and CK-MB levels or arterial blood gas levels between the ROSC and non-ROSC groups (all P >.05).Ten (38.5%) of the patients died within the first 24 hours after ROSC, whereas 16 (61.5%) survived longer than 24 hours. Serum copeptin levels were significantly lower in patients who survived longer than 24 hours compared with those who died within the first 24 hours. Moreover, the mean CPR duration was significantly lower in patients surviving more than 24 hours compared with less than 24 hours. The serum copeptin level may serve as a guide in diagnostic decision making to predict ROSC in patients undergoing CPR and determining the short-term prognosis of patients with ROSC.

Room-Temperature, Highly Durable Ti3C2Tx MXene/Graphene Hybrid Fibers for NH3 Gas Sensing.

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.

Synthesis of novel BiVO4/Cu2O heterojunctions for improving BiVO4 towards NO2 sensing properties

To develop a high sensitive and low temperature NO2 gas sensor, the novel BiVO4/Cu2O heterojunctions were synthesized by a modified metal organic decomposition method to decorate BiVO4 nanoplates using Cu2O nanoparticles for enhancement of BiVO4 sensing performance to NO2. The structure and morphology of BiVO4, Cu2O and BiVO4/Cu2O composites were characterized by XRD, SEM and TEM spectra. The results indicate that the BiVO4/Cu2O heterojunctions are composed of monoclinic BiVO4 nanoplates with the thickness about 1.0–1.2 μm and 30–40 nm diameters of cubic Cu2O nanoparticles. The gas-sensing tests display that the composite exhibits rapid and linear responses to low concentration NO2 (from 100 ppb to 8.0 ppm), the highest response reaches 4.2 towards 4 ppm NO2 at 60 °C and relative humidity of 28.3%, which is more than 2 times of pure BiVO4 at the same condition. The enhanced sensing properties benefit from the novel p-n heterojunction between BiVO4 and Cu2O, which forms a depletion layer at the interface, leading to resistance increase of composites in NO2. The work demonstrates the as-synthesized BiVO4/Cu2O is a promising sensing material to detect NO2 gas.

High sensitive gas sensor based on vertical graphene field effect transistor

A gas sensor made from graphene vertical field effect transistor (VGr-FET) has been fabricated using graphene as the source electrode, C60 thin film as the semiconductor layer and aluminum thin film as the drain electrode. The on/off ratio of transistor gated by bottom electrode with ionic liquid gel as dielectric layer is derived to be 103 from measured source–drain current Ids. The apparent energy barrier height between the graphene and polycrystalline fullerene was calculated from the model of heterojunction diode I–V response curves. The barrier height φBH was altered by the gating potential vertically applied on graphene sheet, resulting the large on/off ratio of the transistor. The effect of surface adsorption of water vapor, oxygen, ammonia and isoprene gas phase molecules on the Ids was measured. The lower limit of detection (LOD) for ammonia (86 ppb) than that of isoprene (420 ppb) is attributed to the donor nature of ammonia contact with p-type graphene, and the adsorbed donor leads to a corresponding positive gating effect to the VGr-FET. This facile, low cost and quick responsive device shows promise for early diagnose of severe human respiratory diseases.

Synthesis and high ammonia gas sensitivity of (CH3NH3)PbBr3-xIx perovskite thin film at room temperature

A new organic inorganic hybrid perovskite material of MAPbBr3-xIx has been synthesized via a simple one step spinning method. The crystal structure, microstructure and surface morphologies, surface physic-chemical state were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy dispersion spectrum (EDS), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). Meanwhile, ammonia, ethanol and acetone sensing tests were evaluated at room temperature of 15°C and the results show favourable response and selectivity towards ammonia. The gas sensing mechanism of MAPbBr3-xIx perovskite based sensor is also discussed. In ammonia gas sensing process, the adsorption, cation exchange and the reversible weak bonding between MA+ and NH4+ dominate the response and recovery processes. Furthermore, long time and high concentration ammonia gas exposure might accelerate the irreversible decomposition of MAPbBr3-xIx perovskite, which results in a decline in response value. To acetone and ethanol gases, the physical reversible tranfer of electrons from gas molecules to intrinsic bromide vacancies and uncoordinated Pb2+ cations in MAPbBr3-xIx perovskite might be the core of the gas sensing process, which results in short response-recovery time (less than 20 s), good repeatability, stability in wider range of gas concentration.

Gas-Sensing Properties of Thin Films Grown on the Surface of InP Single Crystals by Thermal Oxidation

Thin nanofilms have been grown on the surface of single-crystal InP wafers using PbO + V2O5 mixtures in the gas phase. The oxide mixtures used as chemical stimulators have been shown to accelerate the thermal oxidation of InP. The resultant films exhibit gas-sensing properties for ammonia (concentration of 140 ppm) and carbon monoxide (95 ppm). The highest gas sensitivity is near 1.2 arb. units, at temperatures in the range 200–240°C.

Flexible ZnO/PANI/nonwoven nanocomposite based high-sensitive NH3 gas sensor via vapor phase polymerization method

A new synthetic method to flexible sensor towards NH3 with response magnitude as high as 4300% was based on vapor phase polymerization (VPP), where zinc oxide (ZnO) sheets were exposed to polyaniline (PANI) vapors on the flexible nonwoven fabric substrate. A possible brick wall masonry assembly structure of ZnO and PANI on the surface of nonwoven fabric was provided, which also possessed excellent mechanical flexibility and thermostability. The response value of flexible ZnO/PANI/nonwoven sensor increased from 5% to 4300% with the NH3 concentration varied over a wide range (0.5–10 ppm) at room temperature. Flexible and conductive ZnO/PANI/nonwoven composite material has good potential applications as NH3 gas sensor in environment monitoring components and wearable flexible devices.