Chemiresistive Gas Sensors Research Articles

Organic‐Based Chemiresistive Sensors for Detection of Water‐Soluble Gases: Strategies and Roadmap for Enhancing Sensing Performance

AbstractTraditional organic‐based chemiresistive sensors have been a key area of research due to their portability, low power consumption, low cost, turnability, and possibility for miniaturization. However, their real‐world applications have remained restricted by their low selectivity, low sensitivity, and low stability under demanding conditions, such as extreme temperature, humidity, and pH. As such, this review aims to lay the foundation for enhancing the performance of these gas sensors via chemical and physical modifications. To this end, an insight into the building blocks of chemiresistive gas sensors and the attributes of the main four gases (ammonia, carbon dioxide, hydrogen sulfide, and nitrogen dioxide) under aqueous conditions are provided. Such features ultimately determine the enhancement strategy that is best suited to improve the chemiresistive gas sensors performance. Furthermore, this article provides an outlook into the current bottleneck in sensor development and its translation from lab to end‐consumer use. Overall, this review aims to serve as a roadmap for developing next‐generation, high performing chemiresistive gas sensors.

Trace detection of benzene, toluene and xylene (BTX) by chemiresistive metal oxide-based gas sensors: Recent advances in heterojunction materials design

Trace detection of benzene, toluene and xylene (BTX) by chemiresistive metal oxide-based gas sensors: Recent advances in heterojunction materials design

MOF nanoflowers-based flexible portable NO sensors for human airway inflammation detection

The concentration of nitric oxide (NO) in exhaled breath is linked to respiratory diseases, requiring precise detection. Traditional two-dimensional (2D) carbon-based materials used in chemiresistive gas sensors suffer from high detection limits due to a lack of functional sites, while metal oxide sensors are limited by poor selectivity and high operating temperatures, restricting their development. Recently, metal–organic frameworks (MOFs) have emerged as an effective material for NO monitoring due to their superior selectivity; however, their inherent insulating properties hinder practical use. In this study, we synthesized Ni, Co-MOF-74-Carbon Nanotube (CNT) heterostructured nanoflowers, leveraging their bimetallic active sites and large specific surface area to enhance NO adsorption. This composite material, integrated with breathable nanofibrous membranes through physical deposition, exhibits high selection to NO, achieving a linear response range of 30 to 1000 ppb at room temperature and a limit of detection (LOD) of 18.6 ppb. This sensor can accurately detect NO levels in the exhaled breath of both healthy and diseased individuals, confirming its potential for respiratory disease diagnosis. Additionally, we developed a portable device integrating the Ni, Co-MOF-74-CNT- polyacrylonitrile (PAN) membrane, a microcontroller unit (MCU), and a Bluetooth module for real-time NO detection. The systematic design and successful validation of this portable gas sensor pave the way for future home-based real-time monitoring of airway inflammation.

Selective Identification of Hazardous Gases Using Flexible, Room-Temperature Operable Sensor Array Based on Reduced Graphene Oxide and Metal Oxide Nanoparticles via Machine Learning.

Selective detection and monitoring of hazardous gases with similar properties are highly desirable to ensure human safety. The development of flexible and room-temperature (RT) operable chemiresistive gas sensors provides an excellent opportunity to create wearable devices for detecting hazardous gases surrounding us. However, chemiresistive gas sensors typically suffer from poor selectivity and zero-cross selectivity toward similar types of gases. Herein, a flexible, RT operable chemiresistive gas sensors array is designed, featuring reduced graphene oxide (rGO) and rGO decorated with zinc oxide (ZnO), titanium dioxide (TiO2), and tin dioxide (SnO2) nanoparticles (NPs) on a flexible polyimide (PI) substrate. The sensor array consists of four different sensing layers capable of the selective identification of various hazardous gases such as NO2, NO, and SO2 using machine learning (ML). The gas sensor array exhibits a stable response even when mechanically deformed or exposed to high humidity (up to 60%). Each gas sensor, due to the different metal oxide NPs, shows unique responses in terms of sensitivity, responsiveness, response time, and recovery time to different gases. Consequently, the sensor array generates distinct response patterns that effectively differentiate between the target gases. By leveraging these distinctive recovery patterns and employing a data fusion approach in ML, specific concentrations of target gases can be distinguished. Using ML with fused array sensing data, the training and test accuracies achieved were 98.20 and 97.70%, respectively. This innovative combination of sensor arrays and ML offers significant potential for selective gas detection in environmental monitoring and personal safety applications.

Selective passivation of 2D MoS2 nanosheets surface defects by spontaneous growth of Au nanoparticles for full response-recovery NO2 detection at room temperature

Full recovery at room temperature (RT) is quite challengng for two dimensional transition metal dichalcogenides chemiresistive gas sensors. The main reason for the incomplete recovery is the strong bonding of gas molecules onto sensing layer defects. Here, we show that the recovery rate of MoS2 chemiresistive NO2 sensors can be improved by selective passivation of MoS2 nanosheets (NSs) defects with Au nanoparticles (NPs) via a simple spontaneous reduction method. MoS2 NSs were produced by liquid shear exfoliation. Pristine and Au NPs functionalized MoS2 were characterized using ς-potential, UV–Visible spectroscopy, TEM, SEM, AFM, EDS, XRD, XPS and Raman spectroscopy. The analyses confirm the presence of Au NPs on the edges of MoS2 NSs at defective sites with NP sizes of 1–4 nm and 5–30 nm. Both pristine MoS2 and Au-decorated MoS2 NSs were employed to fabricate NO2 chemiresistive devices. Au-decorated MoS2 sensors showed an improved performance (for 1 ppm NO2, Au-MoS2 sensor exhibited a response of 5.6 % instead of 2.2 % for MoS2 sensor), and gave faster response and better recovery time. Concurrently, the functionalization is independent of the adsorption and desorption of NO2. Most importantly, the functionalization of MoS2 NSs helps to full response-recovery within one hour, without either thermal or UV irradiation treatment.

Advances in Gas Detection of Pattern Recognition Algorithms for Chemiresistive Gas Sensor

Gas detection and monitoring are critical to protect human health and safeguard the environment and ecosystems. Chemiresistive sensors are widely used in gas monitoring due to their ease of fabrication, high customizability, mechanical flexibility, and fast response time. However, with the rapid development of industrialization and technology, the main challenges faced by chemiresistive gas sensors are poor selectivity and insufficient anti-interference stability in complex application environments. In order to overcome these shortcomings of chemiresistive gas sensors, the pattern recognition method is emerging and is having a great impact in the field of sensing. In this review, we focus systematically on the advancements in the field of data processing methods for feature extraction, such as the methods of determining the characteristics of the original response curve, the curve fitting parameters, and the transform domain. Additionally, we emphasized the developments of traditional recognition algorithms and neural network algorithm in gas discrimination and analyzed the advantages through an extensive literature review. Lastly, we summarized the research on chemiresistive gas sensors and provided prospects for future development.

Ultrathin Copper Monosulfide Films for an Optically Semitransparent, Highly Selective Ammonia Chemosensor.

Transition-metal sulfides are emerging as promising materials for chemiresistive gas sensors─a field still dominated by semiconducting metal oxides. Despite the availability of materials with tunable electronic, optical, physical, and chemical properties, few studies have moved beyond synthesis to provide strategies for enhancing gas sensing performance through material modification. Here, we present a simple, scalable synthetic strategy for developing an optically semitransparent, flexible NH3 gas sensor with a highly uniform, ultrathin CuS (covellite) active sensing layer. The optical and chemical properties of the CuS were precisely controlled near the percolation threshold of thin-film formation by varying key experimental parameters such as the Cu film thickness (<10 nm) and the sulfurization time (∼90 s) under ambient conditions. Experimental and computational studies of CuS and its NH3 sensing characteristics identify key physicochemical properties. The controlled surface chemistry and morphology of the ultrathin CuS layer demonstrate its effectiveness in functional NH3 sensing devices, which achieve a calculated detection limit of 1.38 ppm for NH3 gas at 150 °C, along with exceptional mechanical robustness and optical semitransparency in the visible-light spectrum.

Ultrasensitive detection of hazardous gas at room temperature enabled by MOF@MXene 0D-2D heterostructure

Achieving high sensitivity in detecting trace concentrations of toxic gases, particularly under room temperature (RT) conditions, remains a significant challenge. Herein, a 0D-2D heterostructure that can detect ppb-level H2S at RT is proposed by self-assembling cobalt-based metal–organic framework (Co-MOF) on Ti3C2Tx MXene. Co-MOFs with high specific surface areas can capture and concentrate target gas molecules, enhancing host-guest interactions and thereby boosting the selectivity and sensitivity. MXene nanosheets with high conductivity enable rapid electron transport at heterointerface, hence efficiently accelerating the reaction kinetics. Thereby, the as-prepared chemiresistive gas sensor based on Co-MOF@MXene 0D–2D heterostructure possessed excellent sensitivity against interfering gases and delivered an excellent response value of 11.1 to 400 ppb H2S at RT. The judicious design of MOF@MXene heterostructure may spur advanced hybrid material systems for superior sensing applications.

Two-dimensional p-n heterojunctions of black phosphorus nanosheet-sensitized α-MoO3 nanoflake for low-temperature chemiresistive NH3 recognition

Of diverse NH3 gas-detection strategies applied in the fields of individual healthcare and industrial production, chemiresistive gas sensors gain the most popularity owing to the superior merits of low cost, convenient signal processing and high sensitivity. However, severe challenges still exist such as elevated operation temperature (>200 °C), limited sensitivity and unsatisfactory selectivity especially under low-concentration and high-humidity conditions. To overcome these hindrances, a sensing layer of black phosphorus nanosheets (BP)-modified α-MoO3 nanoflakes was prepared in this work. After subtle optimization of ingredient composition and operation temperature, the composite sensor S2 could recognize NH3 gas with the concentration spanning from 0.4 to 25 ppm at 40 °C. In particular, a larger mean response (27 % vs. ∼ 2.3 %) with a response/recovery speed of 275/388 s toward 10 ppm NH3 and lower detection of limit (LoD, 0.4 ppm vs. 10 ppm) was achieved with respect to pure BP counterpart. In addition, excellent repeatability, selectivity, long-term stability and humidity-tolerant features were demonstrated for Sensor S2. The improved sensing performance after α-MoO3 incorporation was primarily ascribed to abundant p-n heterojunctions, excellent conductivity of BP and hydrophilic MoO3 that mitigated the water corrosion effect on susceptible BP nanosheets. This work offers an alternative strategy for sensitive and low-temperature NH3 detection, and well cater for the demanding requirements of high sensitivity and low-power consumption in the field of novel gas sensors applicable in the future Internet of Things and exhaled breath-oriented medical diagnosis.

Low-Power Chemiresistive Gas Sensors for Transformer Fault Diagnosis.

Dissolved gas analysis (DGA) is considered to be the most convenient and effective approach for transformer fault diagnosis. Due to their excellent performance and development potential, chemiresistive gas sensors are anticipated to supersede the traditional gas chromatography analysis in the dissolved gas analysis of transformers. However, their high operating temperature and high power consumption restrict their deployment in battery-powered devices. This review examines the underlying principles of chemiresistive gas sensors. It comprehensively summarizes recent advances in low-power gas sensors for the detection of dissolved fault characteristic gases (H2, C2H2, CH4, C2H6, C2H4, CO, and CO2). Emphasis is placed on the synthesis methods of sensitive materials and their properties. The investigations have yielded substantial experimental data, indicating that adjusting the particle size and morphology structure of the sensitive materials and combining them with noble metal doping are the principal methods for enhancing the sensitivity performance and reducing the power consumption of chemiresistive gas sensors. Additionally, strategies to overcome the significant challenge of cross-sensitivity encountered in applications are provided. Finally, the future development direction of chemiresistive gas sensors for DGA is envisioned, offering guidance for developing and applying novel gas-sensitive sensors in transformer fault diagnosis.

Chemiresistive flexible gas sensor for NO2 sensing at room-temperature using in situ constructed Au@In2S3/In2O3 hybrid microflowers

The construction of a novel Au nanoparticles loaded In2S3/In2O3 hybrid microflowers composite was conducted through a well-designed hydrothermal and partial oxidation method and used for NO2 sensing at room-temperature (RT). The characterization data confirmed the hybrid structures and demonstrated that the ratio of adsorbed oxygen species on the surface increased after partial oxidation. The sensing performance of flexible gas sensors based on In2S3/In2O3, In2O3, AuxIn2S3/In2O3 (x = 0.5, 1 and 2 wt%) were tested and compared at RT. Heterostructure construction and Au NPs loading significantly improved the sensing properties at RT. Peculiarly, the response value of 1 wt% Au NPs loaded In2S3/In2O3 (Au1In2S3/In2O3) sensor for 100 ppm NO2 at RT was 20.7, which was 9.2 times higher than that of In2O3 sensor. Meanwhile, it also possessed excellent selectivity, fast response/recovery time (12/27 s), good repeatability, long-term and mechanical stability. The outstanding sensing performance for NO2 at RT mainly associated to the heterojunction between In2S3 and In2O3 and the catalytic effect of Au NPs. Finally, density functional theory (DFT) was used to calculate and analyze the gas adsorption and charger transfer, which related to the enhanced sensing performance.

High performance chemiresistive carbon-nanotube ammonia gas sensor surface modified by tantalum oxide (Ta2O5) metal nanoparticles

High performance chemiresistive carbon-nanotube ammonia gas sensor surface modified by tantalum oxide (Ta2O5) metal nanoparticles

Unraveling the Effect of Oxygen Vacancy on WO3 Surface for Efficient NO2 Detection at Low Temperature.

Oxygen vacancies (VO) in metal oxide semiconductors play an important role in improving gas-sensing performance of chemiresistive gas sensors. Nonetheless, there is still a lack of clear understanding of the inherent mechanism of the influence of oxygen vacancies on gas sensing due to generally focusing on the concentration of VO. Herein, oxygen vacancies were rationally modulated in WO3 nanoflower structures via an annealing process, resulting in a transformation of VO from neutral (VO0) to a doubly ionized (VO2+) state. Density functional theory (DFT) calculations indicate that VO2+ is significantly more efficient than VO0 for NO2 detection in competition with atmospheric O2. Benefiting from a high concentration of VO2+, the WO3-450 (WO3 annealed at 450 °C) sensor exhibits excellent sensing performance with an ultrahigh sensitivity (3674.1 to 5 ppm NO2), superior selectivity, and long-term stability (one month). Furthermore, the sensor with the wide range of concentration detection not only can detect NO2 gas with parts per million (ppm) but also can detect NO2 with parts per billion (ppb) level concentration, with a high sensibility reaching 2.8 to 25 ppb NO2 and over 100 to 100 ppb NO2. This study elucidates the oxygen vacancy mediated sensing mechanism toward NO2 and provides an effective strategy for the rational design of gas sensors with high sensing performance.

Vertically aligned 2D tin sulfide (SnS) nanoplates for selective detection of ethanol gas at room temperature

Abstract Detection of ethanol gas quickly and efficiently at room temperature is crucial for ensuring environmental, human as well as industrial safety. In this work, we have demonstrated a chemiresistive room temperature ethanol gas sensor based on vertically aligned tin sulfide (SnS) nanoplates. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and Brunauer–Emmett–Teller (BET) analysis have revealed the formation of orthorhombic, vertically aligned SnS nanoplates with high specific surface area. The sensor has been fabricated by depositing the SnS powder sample on ITO sheets using electrophoretic deposition (EPD), followed by the deposition of silver (Ag) electrodes using the thermal evaporation technique. The sensor obtained has exhibited a response value (R g/R a) of 17.4–400 ppm ethanol gas concentration, a quick response, and a recovery time of 12.4 s and 20.2 s at room temperature. The sensor has demonstrated long-term stability of 15 min, impressive selectivity, and remarkable repeatability across three successive test cycles of ethanol gas at 400 ppm. Based on the experimental sensing results, a plausible mechanism has been proposed for the sensor. The sensing response of SnS-based sensor at room temperature expands its potential for innovative applications across industries, marking a significant advancement in sensing technology.

Chemiresistive room temperature H2S gas sensor based on MoO3 nanobelts decorated with MnO2 nanoparticles

In this work, we develop ultrafast detection and reversible H2S gas sensor at room temperature (RT, 23 ℃). The optimized MoO3/MnO2 (MM-10) sensor exhibits remarkable sensitivity to H2S with a response of 32.51–100 ppm H2S at RT, which is approximately 21.82 times higher than that of the MoO3 sensor. Further, the MM-10 sensor demonstrates a fast response of 5.71–1000 ppb H2S with response/recovery times of 40/42 s at RT. More surprisingly, the theoretical limit of the MM-10 sensor for detecting H2S gas is as low as 4.58 ppb at RT, which addresses the limitation of binary heterojunction-based sensors in detecting ppb-level H2S gas at RT. After 49 days, the MM-10 sensor still demonstrates reliable stability, ensuring the long-term detection to ppb-level H2S at RT in practical applications. Notably, as the relative humidity increases from 30 % to 90 %, the response only decreases by about 17 %, indicating an excellent shielding ability against water molecules. Additionally, it is found that 1 % relative humidity change has a comparable effect on MM-10 sensor as approximately 5.58 ppb H2S gas. The significant enhancement mechanism on the sensing surface in the context of H2S/MoO3/MnO2 interaction is also thoroughly discussed.

Highly selective sustainable ethanol gas sensor based on p-p heterojunction of SnS/MoSe2 nanocomposite at room temperature

Herein, a high-performance chemiresistive ethanol gas sensor operating at room temperature (RT) is demonstrated based on SnS/MoSe2 nanocomposite. The ethanol-sensing capabilities of the pristine-SnS and SnS/MoSe2 nanocomposite sensor are examined by exposing it to various ethanol concentrations ranging from 50 to 400 ppm at room temperature (RT). The sensing device based on the nanocomposite exhibits a high gas sensing response (Rg/Ra) of 26.8 to 400 ppm for ethanol gas. This results in improved response and recovery times of 9.1 s and 15.7 s respectively, along with high stability, selectivity, and reproducibility. Employing heterojunction in gas-sensing is an effective method for boosting the gas-sensing capabilities of 2D semiconductors. However, selecting semiconductors with compatible energy bands is equally crucial for optimizing gas sensing performance. The synergy arising from the p-p type heterojunction of SnS nanoplates and MoSe2 nanosheets is observed to enhance the sensor's response to ethanol gas. The sensing mechanism of the SnS/MoSe2 nanocomposite sensor is attributed to the formation of p-p heterojunction, modulation of the potential barrier, and charge carrier transfer. The findings suggest that the SnS/MoSe2-based nanocomposite stands out as a potential candidate for fabricating high-performance ethanol gas sensors for electronic applications in environmental monitoring.

Machine Learning‐Assisted Research and Development of Chemiresistive Gas Sensors

Machine Learning‐Assisted Research and Development of Chemiresistive Gas Sensors

Room temperature detection of isopropyl alcohol using CTAB-assisted silver-doped ZnO nanorods as chemiresistive gas sensor

In this study, pristine silver-doped zinc oxide (Ag–ZnO) and Plumbago zeylanica leaf extract (PZE) incorporated with Ag–ZnO, along with the additional material of cetyltrimethylammonium bromide (CTAB)-assisted Ag–ZnO nanorods, were synthesized and extensively characterized. The basic properties of the samples were studied and optimized. Gas sensing measurements were conducted, and the obtained results were thoroughly interpreted. The study includes demonstrating and examining pure Ag–ZnO, PZE-added Ag–ZnO, and CTAB-assisted Ag–ZnO. Notably, the presence of CTAB exhibited a favorable effect on the Ag–ZnO, indicating an enhanced isopropyl alcohol gas sensing response time of 20 s at 15 ppm within an ambient temperature. Additionally, improvements in selectivity and reduced sensor resistance in current (nanoampere - nA) were observed in CTAB-assisted Ag–ZnO. The sensing mechanism was investigated, focusing on the depletion layer of Ag–ZnO with the surfactant. The work emphasizes the sensing abilities of PZE-assisted Ag–ZnO and CTAB Ag–ZnO, highlighting the significance of these noble metals in systematic gas sensing applications.

Spontaneously decorated palladium nanoparticles on redox active covalent organic framework for chemiresistive hydrogen gas sensing

A rapid hydrogen (H2) sensor operating at room temperature is fabricated using covalent organic framework (COF), namely Pyromellitic dianhydride and tris(4-aminophenyl)amine (PMDA-TAPA), PT COF that has a unique ability to spontaneously reduce Pd2+ into Pd0 nanoparticles without the aid of external reducing agents. The presence of surface redox sites in COF enable the rapid formation of Pd nanoparticles on COF surface under ambient conditions. The generated material, hitherto named as Pd@amicPT portrayed remarkable H2 sensing characteristics with a rare combination of high response % (67.3 ± 1) and rapid response/recovery times (5.3/3.5 s, respectively) for 1 % H2 under ambient conditions. Our results demonstrated appreciable reproducibility, repeatability, and long term stability of sensor that remained unaffected by relative humidity and a high selectivity towards H2. Further, sensor performance is found to be superior when compared to many Pd loaded 2D material based chemiresistive H2 gas sensors.

Cobalt-Doped Ceria Sensitizer Effects on Metal Oxide Nanofibers: Heightened Surface Reactivity for High-Performing Chemiresistive Sensors.

Chemiresistive gas sensors based on semiconducting metal oxides typically rely on noble metal catalysts to enhance their sensitivity and selectivity. However, noble metal catalysts have several drawbacks for practical utilization, including their high cost, their propensity for spontaneous agglomeration, and poisoning effects with certain types of gases. As such, in the interest of commercializing the chemiresistive gas sensor technology, we propose an alternative design for a noble-metal-free sensing material through the case study of Co-doped ceria (Co-CeO2) catalysts embedded in a SnO2 matrix. In this investigation, we utilized electrospinning and subsequent calcination to prepare Co-CeO2 catalyst nanoparticles integrated with SnO2 nanofibers (NFs) with uniform particle distribution and particle size regulation down to the sub-2 nm regime. The resulting Co-CeO2@SnO2 NFs exhibited superior gas sensing characteristics toward isoprene (C5H8) gas, a significant biomarker for monitoring the onset of various diseases through breath diagnostics. In particular, we identified that the Co-CeO2 catalysts, owing to the transition metal doping, facilitated the spillover of chemisorbed oxygen species to the SnO2 sensing body. This resulting in the sensor having a 27.4-fold higher response toward 5 ppm of C5H8 (compared to pristine SnO2), exceptionally high selectivity, and a low detection limit of 100 ppb. The sensor also exhibited high stability for prolonged response-recovery cycles, attesting to the strong anchoring of Co-CeO2 catalysts in the SnO2 matrix. Based on our findings, the transition metal-doped metal oxide catalysts, such as Co-CeO2, demonstrate strong potential to completely replace noble metal catalysts, thereby advancing the development of the commercially viable chemiresistive gas sensors free from noble metals, capable of detecting target gases at sub-ppm levels.