Gas Sensor Platform Research Articles

Highly Selective Ammonia Detection in NiO‐Functionalized Graphene Micropatterns for Beef Quality Monitoring

AbstractGraphene has emerged as one of the most promising materials for next‐generation gas sensor platforms due to its high flexibility, transparency, and hydrophobicity. However, graphene shows inherent low selectivity in gas sensing. This has led to extensive development of noble‐metal decoration on graphene to modulate its surface chemistry for enhanced selectivity. While noble metals such as Pt, Pd, and Au have widely been employed to functionalize graphene surface, non‐noble metal decoration of graphene has remained underexplored. Here, an unprecedented room‐temperature self‐activated graphene gas sensor functionalized by NiO nanoparticles and its application to wearable devices monitoring ammonia gas in daily life are demonstrated. NiO‐functionalized graphene micropatterns show ultra‐high selectivity to ammonia with a low detection limit of 2.547 ppt. Density functional theory (DFT) calculations reveal that the strong attraction between NiO and NH3 induced by charge depletion and the vertex region of NiO accelerate the adsorption of NH3 molecules. Furthermore, a wearable graphene device demonstrates the capability to detect ammonia emissions from beef, triggering an alarm call when a specific threshold is exceeded. This work proposes the functionalization of graphene with transition metal oxides, extending beyond the conventional noble metal decoration, and the potential utilization of the graphene for wearable devices.

Real-Time Tunable Gas Sensing Platform Based on SnO2 Nanoparticles Activated by Blue Micro-Light-Emitting Diodes

HighlightsBlue micro-light-emitting diodes (μLED)-integrated gas sensors were fabricated as monolithic structure by directly loading sensing materials onto the μLED.SnO2 nanoparticles are activated by blue μLED and exhibit outstanding sensitivity to NO2 at μ-Watt power levels.Noble metal (Au, Pd, Pt)-decorated SnO2 showed the tunable gas selectivity for 4 target gases under blue light illumination.

Reliability of FET-type gas sensor with asymmetric air-gap micro-heater structure considering thermoelectric effect

Poly-silicon has a wide range of applications because of its interesting properties in the thermoelectric effect. We propose an optimal field-effect transistor-type (FET-type) gas sensor platform with an embedded poly-silicon micro-heater designed considering both power consumption and reliability. Since the poly-silicon micro-heater has a thermoelectric effect, the reliability of the micro-heater can be improved without a significant increase in power consumption by adopting asymmetric etch-holes (finally asymmetric air-gap) along the heater electrode. The sensor with the shorter etch-hole (10 µm) around one electrode of the heater electrode increases power consumption by only 1.22 times but can increase lifetime by 14.2 times. The heat distribution and contact temperature of symmetric and asymmetric air-gap heaters are compared using COMSOL Multiphysics. Sensors with different lengths of etch-holes are fabricated, and the thermal response and reliability of the fabricated sensors are measured and analyzed. In addition, in a sensor in which a thin film of indium oxide is deposited as a sensing material on the gas sensor platform, the effect of air-gap design change on the gas sensing characteristics is investigated. Depending on the polarity of the voltage applied between the two terminals of the heater, the difference in void formation and damage at the heater contacts is confirmed by TEM and EDS analysis.

The Networked Nitrous Node: A Low-Power Field-Deployable COTS-Based N$_{2}$O Gas Sensor Platform

We present a wireless nitrous oxide (N <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> O) gas sensor system consisting of a commercial high-current infrared N <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> O sensor wrapped in a “smart” sensor framework to make it suitable for battery-powered deployment. This framework consists of wireless mesh networking, data storage, additional environmental sensors, and a gas sensor power control circuit managed by a central microcontroller. The N <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> O sensor is the first order consumer of power and sampling N <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> O at approximately ten minute intervals yields an estimated system lifetime of 63 days when using four 18650 Li-ion batteries. The node stores data locally on SD card and wirelessly reports to a root PC that also stores data and displays to users in a simple graphical user interface. The system is composed of majority off-the-shelf components and any custom components were designed or programmed with open-source software. We expect these features will lead to this system being more easily understood, copied, and modified by engineers wishing to design similar sensor system frameworks and thereby allow even more power-prohibitive devices to be wirelessly deployed.

Polymer Ring-Flexure-Membrane Suspended Gate FET Gas Sensor: Design, Modelling and Simulation.

This work reports the design, modelling, and simulation of a novel polymer MEMS gas sensor platform called a ring-flexure-membrane (RFM) suspended gate field effect transistor (SGFET). The sensor consists of a suspended polymer (SU-8) MEMS based RFM structure holding the gate of the SGFET with the gas sensing layer on top of the outer ring. During gas adsorption, the polymer ring-flexure-membrane architecture ensures a constant gate capacitance change throughout the gate area of the SGFET. This leads to efficient transduction of the gas adsorption-induced nanomechanical motion input to the change in the output current of the SGFET, thus improving the sensitivity. The sensor performance has been evaluated for sensing hydrogen gas using the finite element method (FEM) and TCAD simulation tools. The MEMS design and simulation of the RFM structure is carried out using CoventorWare 10.3, and the design, modelling, and simulation of the SGFET array is carried out using the Synopsis Sentaurus TCAD. A differential amplifier circuit using RFM-SGFET is designed and simulated in Cadence Virtuoso using the lookup table (LUT) of the RFM-SGFET. The differential amplifier exhibits a sensitivity of 2.8 mV/MPa for a gate bias of 3 V and a maximum detection range of up to 1% hydrogen gas concentration. This work also presents a detailed fabrication process integration plan to realize the RFM-SGFET sensor using a tailored self-aligned CMOS process adopting the surface micromachining process.

Defect engineering of nanostructured ZnSnO3 for conductometric room temperature CO2 sensors

Slow response/recovery kinetics and high limit of detection (LOD) are crucial challenges for practical room-temperature carbon dioxide (CO2) gas sensor platforms. Herein, visible light-excited ZnSnO3 three-dimensional nanostructures are utilized for highly sensitive and selective detection of CO2. The sensing performance reveals that fine-controlled oxygen vacancy (OV) and highly-active electron transition of defect-rich nanomaterials are obtained via modulating the hydrogen treatment duration, conducive to the prominently enhanced ppm-level CO2 response with low LOD (3.05 ppm), ultrafast response time (16.814 s) and improved stability (14.658 ± 2.339 @ 400 ppm for 14 days) among all the reported ternary metal oxide semiconductor (TMOS) -based gas sensors. The photophysical enhancement mechanism of analyte is discussed in detail by combining experimental and theoretical investigation through the effect of photoexcitation on both adsorbed CO2 molecules and sensing materials, the role of pre-adsorbed oxygen for regulating targeted gas interaction, the changes of electronic transition in the bandgap, the impact of in-plane OV and bridging OV on CO2 sensing, and the function of OV for modifying the coordination sites and geometry of metal cations at the surface. From a broader perspective, the fabricated sensor provides a remarkably facile and effective technique for rapid and repeatable CO2 monitoring.

Sensing Properties of g-C3N4/Au Nanocomposite for Organic Vapor Detection

Alleviating the increasingly critical environmental pollution problems entails the sensing of volatile organic compounds (VOCs) as a hazardous factor for human health wherein the development of gas sensor platforms offers an efficient strategy to detect such noxious gases. Nanomaterials, particularly carbon-based nanocomposites, are desired sensing compounds for gas detection owing to their unique properties, namely a facile and affordable synthesis process, high surface area, great selectivity, and possibility of working at room temperature. To achieve that objective, g-C3N4 (graphitic carbon nitride) was prepared from urea deploying simple heating. The ensuing porous nanosheets of g-C3N4 were utilized as a substrate for loading Au nanoparticles, which were synthesized by the laser ablation method. g-C3N4 presented a sensing sensitivity toward organic vapors, namely methanol, ethanol, and acetone vapor gases, which were significantly augmented in the presence of Au nanoparticles. Specifically, the as-prepared nanocomposite performed well with regard to the sensing of methanol vapor gas and offers a unique strategy and highly promising sensing compound for electronic and electrochemical applications.

PdO-Nanoparticle-Embedded Carbon Nanotube Yarns for Wearable Hydrogen Gas Sensing Platforms with Fast and Sensitive Responses

Hydrogen (H2) gas has recently become a crucial energy source and an imperative energy vector, emerging as a powerful next-generation solution for fuel cells and biomedical, transportation, and household applications. With increasing interest in H2, safety concerns regarding personal injuries from its flammability and explosion at high concentrations (>4%) have inspired the development of wearable pre-emptive gas monitoring platforms that can operate on curved and jointed parts of the human body. In this study, a yarn-type hydrogen gas sensing platform (HGSP) was developed by biscrolling of palladium oxide nanoparticles (PdO NPs) and spinnable carbon nanotube (CNT) buckypapers. Because of the high loading of H2-active PdO NPs (up to 97.7 wt %), when exposed to a flammable H2 concentration (4 vol %), the biscrolled HGSP yarn exhibits a short response time of 2 s, with a high sensitivity of 1198% (defined as ΔG/G0 × 100%). Interestingly, during the reduction of PdO to Pd by H2 gas, the HGSP yarn experienced a decrease in diameter and corresponding volume contraction. These excellent sensing performances suggest that the fabricated HGSP yarn could be applied to a wearable gas monitoring platform for real-time detection of H2 gas leakage even over the bends of joints.

A multi-layered graphene based gas sensor platform for discrimination of volatile organic compounds via differential intercalation

Selective and sensitive detection of volatile organic compounds (VOCs) is of critical importance for environmental monitoring, disease diagnosis and industrial applications. Graphene Foam based sensor platform suggests selective determination of VOCs.

Effects of oxygen gas in the sputtering process of the WO3 sensing layer on NO2 sensing characteristics of the FET-type gas sensor

This paper investigates the effect of oxygen gas in the sputtering process of the WO3 sensing layer. The WO3 sensing layer is deposited on the Si FET-type gas sensor platform having horizontal floating-gate (FG) interdigitated with control-gate (CG) by using the DC magnetron sputtering method. When exposed to the NO2 gas, the drain current of the FET-type gas sensor with the WO3 sensing layer increases since the NO2 gas is known as an oxidizing gas. In this work, NO2 sensing characteristics of the gas sensors with the WO3 sensing layer deposited under three different sputtering conditions are compared. The flow rate of argon gas in total sputtering gas is fixed at 30 sccm, and the flow rate of oxygen gas is changed (0, 1, and 3 sccm). NO2 response of the gas sensor with WO3 sensing layer deposited using the oxygen gas with the argon gas in the sputtering process is higher than that of the gas sensor with WO3 sensing layer deposited using only argon gas. As the ratio of oxygen gas in the total sputtering gas increases, the response of the gas sensor increases since the size of the grain is reduced and the number of W = O bonds at the grain boundary increases. Therefore, NO2 response of the FET-type gas sensor with the WO3 sensing layer deposited at an oxygen flow rate of 3 sccm in the sputtering process is the largest. The optimized FET-type gas sensor has excellent selectivity for NO2 target gas.

Multilevel Self-Assembly of Block Copolymers and Polymer Colloids for a Transparent and Sensitive Gas Sensor Platform.

The recent emerging significance of the Internet of Things (IoT) demands sensor devices to be integrated with many different functional structures and devices while conserving their original functionalities. To this end, optical transparency and mechanical flexibility of sensor devices are critical requirements for optimal integration as well as high sensitivity. In this work, a transparent, flexible, and sensitive gas sensor building platform is introduced by using multilevel self-assembly of block copolymers (BCPs) and polystyrene (PS) colloids. For the demonstration of an H2 gas sensor, a hierarchically porous Pd metal mesh structure is obtained by overlaying the two different patterned template structures with synergistic, distinctive characteristic length scales. The hierarchical Pd mesh shows not only high transparency over 90% but also superior sensing performance in terms of response and recovery time owing to enhanced Pd-to-hydride ratio and short H2 diffusion lengths from the enlarged active surface areas. The hierarchical morphology also endows high mechanical flexibility while securing reliable sensing performance even under severe mechanical deformation cycles. Our scalable self-assembly based multiscale nanopatterning offers an intriguing generalized platform for many different multifunctional devices requiring hidden in situ monitoring of environmental signals.

Effect of Ag NPs-decorated carbon nanowalls with integrated Ni-Cr alloy microheater for sensing ammonia and nitrogen dioxide gas

Carbon nanowalls (CNWs), which have high mobility, high surface area and high porosity, generally have high potential as gas sensing materials, but poor gas detection performance has been reported due to low response and recovery. To enhance the sensing performance of a chemiresistive gas sensor based on CNWs, a metallic catalyst and micro heating system have been used. Ag NPs were decorated onto CNWs patterned for fabrication of a gas sensor platform with microheater. Diverse characteristics of functionalized CNWs by Ag NPs were investigated via scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy. Ag NPs or clusters were optically observed among a significant number of pores on the surface of CNWs, resulting in change in pore size. Also, a certain evidence of Ag NPs was demonstrated by surface-enhanced Raman scattering (SERS), causing a positive and negative shift in the Raman band of CNWs. In terms of gas-sensing performance, a greater amount of Ag NPs showed highly improved sensing signal for NH3 and NO2 gas from 25 to 100 ppm compared to pristine conditions. The microheater also improved the poor recovery rate of CNWs. Consequently, the combined gas sensing platform with metallic catalyst and microheating system showed significantly enhanced gas sensing performance.

Experimental Demonstration of Germanium-on-Silicon Slot Waveguides at Mid-Infrared Wavelength

We first demonstrated a slot waveguide based on a Ge-on-Si (GOS) platform with a 3 μm thickness of the Ge in the mid-infrared wavelength range at 4.2 μm. We numerically designed the slot waveguide to have a large field confinement in the slot for sensing application. Based on the design, we fabricated the GOS slot waveguide with a slot gap of 200 nm, which is coupled with in-out grating couplers. We characterized the propagation loss of the waveguides by the cut-back method and carefully compared it with channel waveguides. In fundamental TE mode, the propagation loss in the channel waveguide and the slot waveguide were quite similar (5.20 and 4.86 dB/cm, respectively), whereas the field confinement was much higher in the slot waveguides. Additionally, we simulated and analyzed the loss of the devices in terms of radiation, sidewall roughness scattering, material absorption by free-carrier absorption (FCA), and CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . These results strongly suggest that the fabricated slot waveguide based on the GOS platform would be one of the promising building blocks for the optical gas sensor platform.

Trifluoromethyl ketone P3HT-CNT composites for chemiresistive amine sensors with improved sensitivity

Chemiresistive sensors, wherein conductivity is changed by exposure to analytes, are widely used in various disciplines and in our daily lives. Carbon nanotubes (CNTs) are excellent materials with exceptional conductivity, and polymer/CNT composites have been extensively deployed in chemiresistive sensors. To improve sensitivity, we herein report the covalent functionalization of poly(3-hexylthiophene)s (P3HTs) with highly electrophilic trifluoromethyl ketones, referred to as TFMK-P3HT, and its composite with CNT and amine sensing were investigated. The synthesis was begun with the bromination of commercial P3HT, followed by a lithium-halogen exchange reaction and subsequent quenching with trifluoroacetic anhydride, producing TFMK-P3HT. Homogeneous CNT networks with TFMK-P3HT were confirmed by atomic force microscopy (AFM). The sensing of three representative amines with TFMK-P3HT/CNT showed four times higher sensitivity than P3HT/CNT samples. The sensors were selective to amines and less responsive to competitive gas species such as alcohols and H2S. The sensitivity improvements of the TFMK-P3HT sensor were maintained in humid conditions. This work suggests a facile synthetic method to improve the sensitivity of CNT-based chemical sensors and provides an effective gas sensor platform for the selective detection of amine gas.

Smartphone Case-Based Gas Sensing Platform for On-site Acetone Tracking.

Gas sensor-embedded smartphones would offer the opportunity of on-site tracking of gas molecules for various applications, for example, harmful air pollutant alarms or noninvasive assessment of health status. Nevertheless, high power consumption and difficulty in replacing malfunctioned sensors as well as limited space in the smartphone to host the sensor restrain the relevant advancements. In this article, we create a smartphone case-based sensing platform by integrating the functional units into a smartphone case, which performs a low detection limit of 117 ppb to acetone and high specificity. Particularly, dimming glass-regulated light fidelity (Li-Fi) communication is successfully developed, allowing the sensing platform to operate with relatively low power consumption (around 217 mW). Experimental proof on harmful gas sensing and potential clinic application is implemented with the sensing platform, demonstrating satisfactory sensing performance and acceptable health risk pre-warning accuracy (87%). Thus, the developed smartphone case-based sensing platform would be a good candidate for realizing harmful gas alarms and noninvasive assessment of health status.

Preparation and Characterization of PEDOT:PSS/TiO2 Micro/Nanofiber-Based Gas Sensors.

In this study, we employed electrospinning technology and in situ polymerization to prepare wearable and highly sensitive PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors. PEDOT, PEDOT:PSS, and TiO2 were prepared via in situ polymerization and tested for characteristic peaks using energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR), then characterized using a scanning electron microscope (SEM), a four-point probe resistance measurement, and a gas sensor test system. The gas sensitivity was 3.46–12.06% when ethanol with a concentration between 12.5 ppm and 6250 ppm was measured; 625 ppm of ethanol was used in the gas sensitivity measurements for the PEDOT/composite conductive woven fabrics, PVP/PEDOT:PSS nanofiber membranes, and PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors. The latter exhibited the highest gas sensitivity, which was 5.52% and 2.35% greater than that of the PEDOT/composite conductive woven fabrics and PVP/PEDOT:PSS nanofiber membranes, respectively. In addition, the influence of relative humidity on the performance of the PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors was examined. The electrical sensitivity decreased with a decrease in ethanol concentration. The gas sensitivity exhibited a linear relationship with relative humidity lower than 75%; however, when the relative humidity was higher than 75%, the gas sensitivity showed a highly non-linear correlation. The test results indicated that the PVP/PEDOT:PSS/TiO2 micro/nanofiber gas sensors were flexible and highly sensitive to gas, qualifying them for use as a wearable gas sensor platform at room temperature. The proposed gas sensors demonstrated vital functions and an innovative design for the development of a smart wearable device.

Drone-Mountable Gas Sensing Platform Using Graphene Chemiresistors for Remote In-Field Monitoring.

We present the design, fabrication, and testing of a drone-mountable gas sensing platform for environmental monitoring applications. An array of graphene-based field-effect transistors in combination with commercial humidity and temperature sensors are used to relay information by wireless communication about the presence of airborne chemicals. We show that the design, based on an ESP32 microcontroller combined with a 32-bit analog-to-digital converter, can be used to achieve an electronic response similar, within a factor of two, to state-of-the-art laboratory monitoring equipment. The sensing platform is then mounted on a drone to conduct field tests, on the ground and in flight. During these tests, we demonstrate a one order of magnitude reduction in environmental noise by reducing contributions from humidity and temperature fluctuations, which are monitored in real-time with a commercial sensor integrated to the sensing platform. The sensing device is controlled by a mobile application and uses LoRaWAN, a low-power, wide-area networking protocol, for real-time data transmission to the cloud, compatible with Internet of Things (IoT) applications.

Machine Learning‐Enabled Smart Gas Sensing Platform for Identification of Industrial Gases

Both ammonia and phosphine are widely used in industrial processes, and yet they are noxious and exhibit detrimental effects on human health. Despite the remarkable progress on sensors development, there are still some limitations, for instance, the requirement of high operating temperatures, and that most sensors are solely dedicated to individual gas monitoring. Herein, an ultrasensitive, highly discriminative platform is demonstrated for the detection and identification of ammonia and phosphine at room temperature using a graphene nanosensor. Graphene is exfoliated and successfully functionalized by copper phthalocyanine derivate. In combination with highly efficient machine learning techniques, the developed graphene nanosensor demonstrates an excellent gas identification performance even at ultralow concentrations: 100 ppb NH3 (accuracy—100.0%, sensitivity—100.0%, specificity—100.0%) and 100 ppb PH3 (accuracy—77.8%, sensitivity—75.0%, and specificity—78.6%). Molecular dynamics simulation results reveal that the copper phthalocyanine derivate molecules attached to the graphene surface facilitate the adsorption of ammonia molecules owing to hydrogen bonding interactions. The developed smart gas sensing platform paves a path to design a highly selective, highly sensitive, miniaturized, low‐power consumption, nondedicated, smart gas sensing system toward a wide spectrum of gases.

Superior detection and classification of ethanol and acetone using 3D ultra-porous γ-Fe2O3 nanocubes-based sensor

The assembly of primary nanoparticles to form hierarchical ultra-porous architectures is of great interest in various fields because of their extremely large surface area and porosity. In this work, the 3D ultra-porous γ-Fe2O3 nanocubes were synthesized by a simple method, which was derived from perfect Prussian Blue nanocubes by the oxidative decomposition process. The as-synthesized 3D γ-Fe2O3 nanocubes possess a large specific surface area and high porosity, which arise from the self-assembly of ultrafine nanoparticles. The 3D ultra-porous γ-Fe2O3 nanocubes-based sensors showed superior detection of acetone and ethanol with excellent sensitivity and rapid response time. The fantastic gas-sensing platform of 3D γ-Fe2O3 nanocubes could originate from their unique structures and interesting gas-sensing mechanisms. The linear discriminant analysis (LDA) algorithm was effectively used to discriminate between acetone and ethanol.

In Situ Laser-Assisted Synthesis and Patterning of Graphene Foam Composites as a Stretchable Gas Sensing Platform

In Situ Laser-Assisted Synthesis and Patterning of Graphene Foam Composites as a Stretchable Gas Sensing Platform