Solid-state Gas Sensors Research Articles

Facile synthesis of silver and copper modified graphitic carbon nitride for volatile organic compounds sensing

Volatile organic compounds (VOCs) pose significant health risks when inhaled or ingested in large quantities. Metal oxide-based solid-state gas sensors are commonly utilized for VOCs detection, including methanol, however their high operating temperature and selectivity are both biggest challenges. In this context, graphitic carbon nitride (g-C3N4) has emerged as a promising alternative for VOCs sensing due to its superior sensing properties. In this work, Cu and Ag doped g-C3N4 was synthesized via the polycondensation method for VOCs sensing applications. All the samples showed a selective response to methanol at room temperature. Notably, the Ag/g-C3N4 sensor exhibited a significantly enhanced response (~27.5) compared to both undoped g-C3N4 (~3.58) and Cu/g-C3N4 (~9.82) sensors towards 200 ppm methanol. The Ag/C3N4 based sensor showed rapid response (21 s) and recovery (17 s) times, along with excellent short-term and long-term stability. It was found that Ag/C3N4 sensor exhibited a good response to humidity levels ranging from 9 % to 93 % RH, without any significant variation observed when deposited on the ceramic and flexible polyimide substrates. Further, considering its practical applicability, the Ag/C3N4 sensor showed successful detection of alcohol in human breath, highlighting its potential for real-world applications.

(Invited) Multi-Modal Solid-State Gas Sensors-Based Breath Analysis System with Convolutional Neural Network (CNN) for Early Detection of Lung Cancer

Currently, digital healthcare technologies based on Internet of Things (IOT) are emerging, and the market for digital healthcare was estimated to be 151.5 billion dollars by 2020. Among the digital healthcare technologies, disease diagnosis is attracting maximum attention. Traditional diagnostic methods, such as radiology and human biological material analysis, have limitations of long study time, high cost, radiation exposure, and pain. Therefore, non-invasive diagnostics methods, for early diagnosis of specific diseases and personal healthcare management, have attracted attention.Breath sensors are one of the promising candidates for the realization of non-invasive diagnosis owing to their ease of use, safety, and cost effectiveness. The exhaled breath analysis technique holds great promise as a non-invasive method for diagnosing lung cancer. In the breath of lung cancer patients, various volatile organic compounds (VOCs) markers are generated during metabolic processes. Analyzing these VOCs markers presents a compelling avenue for early and non-invasive lung cancer diagnosis. Solid state gas sensors capable of measuring specific VOCs are currently being researched and utilized as commercial gas sensors for this purpose. However, the concentration of lung cancer VOCs markers in exhaled breath is commonly very low, and individual commercial gas sensors often lack the necessary sensitivity and selectivity to accurately diagnose lung cancer. In this study, we propose a multimodal solid state electronic biosensor system designed to differentiate lung cancer VOCs characteristics among multiple VOCs, enabling exhalation-based lung cancer diagnosis. Initially, we developed multimodal biosensors using more than 20 gas sensors, consisting of metal oxide semiconductor sensors, electrochemical sensors, photoionized detectors, metalorganic frame sensors and so on. And each exhibiting varying sensitivity profiles for complex gas mixtures. Additionally, we designed a classification algorithm based on convolutional neural networks (CNN) and multi-layered perceptron (MLP) to distinguish between lung cancer patients and healthy individuals using the output from these diverse multimodal gas sensors. To evaluate the system's performance, we collected exhaled air samples from 74 lung cancer patients and 107 normal subjects, conducting clinical trials with our developed system. We did model evaluation with confusion matrix and ROC curve. The results of these tests confirmed that our system achieved a high predictive accuracy of over 95% in classifying lung cancer patients. The simplicity of the sensor configuration in our developed system makes it suitable for large-scale screening tests to identify potential candidates for precise lung cancer diagnosis. This technology has the potential to contribute to reduced national welfare costs and improved patient survival rates through early diagnosis.

Green Valorization of Waste Plastics to Graphene as an Upcycled Eco-Friendly Material for Advanced Gas Sensing

The valorization technique successfully transformed waste polyethylene terephthalate (PET) into valuable carbon nanomaterial (CN)/graphene, while doped and undoped ZnO nanopowders were synthesized via sol–gel methods. Utilizing XRD, BET, TEM, EDX, FTIR, and TGA analyses, the synthesis of sp2 2D sheet, pristine, and doped ZnO nanostructures was confirmed. Solid-state gas sensor devices, tested under 51% relative humidity (RH), 30 °C ambient temperature, and 0.2 flow rate, exhibited a 3.4% enhanced response to H2 gas compared to CO2 at 50 ppm concentrations over time. Notably, the ZnO/CN sensor surpassed CN and ZnO alone, attributed to CN dopant integration with decreasing order of response performance as ZnO/CN > CN > ZnO. This study underscores the efficacy of valorization techniques in generating high-value carbon nanomaterials and their efficacy in bolstering gas sensor performance, with ZnO/CN demonstrating superior response capabilities.

Predicting Ozone Depletion using BIn2O3 With RH based Solid Conductometric Sensor

<p>Ozone depletion arises due to the presence of gases like chlorofluorocarbons and halons which are liberated into the atmosphere. The region of earth’s atmosphere named as ozone shield, in which absorbs the ultra violet radiations of the sun. Although, its thickness varies periodically, this layer is primarily located in the lower stratosphere between 15 to 35 kms above the earth. Due to this, the ultraviolet rays directly enter into the earth causes harmful effects little by little on both living and non-living organisms. In this paper, BIn2O3 with rh sensor in co precipitation method is used to detect the ozone depletion and it is based on the solid-state gas sensors. To achieve the excellent performance of an ozone depletion detecting branch like BIn2O3 with rh, this was designed using a simple precipitation method. The coprecipitation method had deposited in BIn2O3 with a thickness of 45 to 50 nanometer. The detection limit of ozone reduced as 30 parts per billion. Further, the gas detector demonstrated high sensitivity and selectivity of the device. The rhodium covers the surface areas ranges from 0 to 0.1. It reaches the accuracy of 96%. According to the degree of rhodium coverage, the sensors will be response to the ozone gas. The oxygen chemisorbed ability and a coverage of a great surface area of BIn2O3 with rhodium highly related to the excellent sensing behavior. This study paves the way for an exact sensing and ppb level detection ozone gas.</p>

Geosmin and 2-Methylisoborneol Detection in Water Using Semiconductor Gas Sensors

Geosmin and 2-methylisoborneol (MIB) are the most common causes of unpleasant odours in drinking water. A method was proposed to detect and recognise these compounds in water and determine their concentrations. The method utilises commercial solid-state gas sensors and data analysis. Sample preparation plays an important role. The aqueous solution is converted into a gas sample using a specially designed dynamic headspace. The responses of the sensors are recorded during exposure to headspace vapours in a dynamic mode. The best limit of detection for geosmin, LOD = 6.20 µg/L, was attained with a TGS2602 sensor. The best limit of detection for MIB, LOD = 0.52 µg/L, was attained with a TGS826 sensor. Geosmin and MIB recognition was 100% successful based on TGS826 and TGS2602 response classifications. Geosmin and MIB concentrations were effectively determined in solutions containing one or both compounds. The respective mathematical models utilised the responses of TGS826 and TGS2602. The smallest concentration prediction error was RMSE = 2.19 µg/L (for geosmin) and RMSE = 0.33 µg/L (for MIB). The study demonstrated the application potential of non-specific gas sensors for the early warning monitoring of geosmin and MIB presence in water. Further studies are needed to develop a system that can be tested in field conditions.

Picoliter drop deposition of SnO2 nanoparticles onto microsensor platforms

Microhotplates produced by micromachining processes provide a robust substrate for miniaturized solid-state gas sensors; however, it can be challenging to locally deposit solution-suspended nanomaterials for sensing directly onto these small (≈ 100 µm), 3-dimensional platforms which are often configured in arrays to increase analytical capabilities. A picoliter drop-deposition technique based on inkjet printing is described here which has been used to achieve accurate, precise drop placement and reproducible film formation. Tin oxide nanoparticles, a well-established sensing material for use in gas sensor devices, were used to demonstrate the methodology. The nanoparticles were synthesized via a hydrothermal route to achieve crystalline materials with an average diameter of 5.5 nm. Tin oxide nanoparticle-laden suspensions were then formulated to reduce agglomeration, enable consistent first-drop formation, and prevent dispenser clogging. A priming technique was developed to accurately and repeatably perform deposition of picoliter-range drops onto the microsensor platforms. The technique was employed with a dynamic drop placement procedure to yield formation of spatially registered mesoporous oxide films on individual microhotplates. Microsensors fabricated with the drop-deposited SnO2 nanoparticles showed sensitive and rapid gas-sensing responses to two reducing gases and one oxidizing gas when tested at concentrations within the range of (5 to 100) µmol/mol. The presented results indicate that the combination of pre-formed nanoparticles and picoliter drop deposition offers a versatile approach for reproducibly manufacturing gas microsensors, which can be adapted for a range of gas sensing materials and microscale platforms.

Multi-Function Sensory System for Detection of Ammonia

Ammonia is a highly toxic gas with implications for human and animal health. This effort aims to develop a low-cost multi-array orthogonal sensor for detecting a low concentration of ammonia in a poultry house. To approach this problem, a novel multi-array electro-thermal and Metal oxide solid state gas sensor are developed. Its design consists of a microfabricated suspended MEMS bridge, a resistance temperature detector (RTD), a low-pass loop filter H(s), and a heater amplifier for the micro-oven. The resistive element is used as the micro-oven heater. The sensing platform comprises of a low-cost thermal conductivity sensor (TCD), and Metal oxide (ZnO, NiO-ZnO, Au-ZnO) solid-state sensors. From this study. we concluded that the thermal conductivity sensor provides a linear level of detection(LOD) of 1 ppm at 30-80 % relative humidity with 100 ns response time and 5 years of lifetime while the Au-ZnO solid state sensor has sub ppm limit of detection and response time of ~ 2 minutes. Figure 1

An in-situ FTIR-LCR meter technique to study the sensing mechanism of MnO2@ZIF-8/CNPs and a direct relationship between the sensitivity of the sensors and the rate of surface reaction

Diethylamine vapor is harmful to people if inhaled or swallowed, as it results in the oxidation of hemoglobin in the body into unwanted methemoglobin, which is unable to transport oxygen in the blood, resulting in reduced blood oxygenation. Lack of blood oxygenation leads to hypoxemia. MnO2 nanorods, carbon soot, and MnO2@ZIF-8 are sensing materials used to prepare solid-state gas sensors that operate at room temperature. The prepared sensing materials were characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The performance of the MnO2@ZIF-8 based sensor improved significantly when the carbon soot was introduced into the composite. The effect of the amount of CNPs in the composite on the performance of the sensors was studied. The MnO2@ZIF-8/CNPs-based sensor with a 3:1 mass ratio was highly selective towards diethylamine vapor over acetone, methanol, ethanol, and 3-pentanone vapors. An in situ FTIR coupled with LCR meter was used to understand the sensing mechanism of diethylamine vapor and it was found that the sensing mechanism was by deep oxidation of diethylamine to CO2, H2O, and other molecules. The sensing mechanism was studied by monitored by CO2 band intensity which was produced from the reaction between the sensing materials and the analyte vapor. As the sensor's exposure time increased the intensity of the CO2 IR band increased. We observed the direct relationship between the surface reaction rate and the sensor's sensitivity.

The Effect of the Working Electrode Material Based on Pt/SnO2(Sb) on the Properties of Hydrogen and Carbon-Monoxide Sensors

The effect of the platinum content (3–10 wt %) in the Pt/SnO2(Sb)-based working-electrode material on the properties (sensitivity, high-speed performance, recovery time) of solid-state potentiometric gas sensors for hydrogen and carbon monoxide including their simultaneous presence in air is studied. Sensors with 5% Pt demonstrate the best characteristics: the efficient carbon-monoxide detection for its concentration from 0.01 to 1 vol %; no effect of hydrogen present in the CO + air mixture in concentrations comparable with the CO concentration; the shortest relaxation time (~30 s at 1% CO).

Electrochemical detection of simple alkanes by utilizing a solid-state zirconia-based gas sensor

Solid-state gas sensors composed of complex oxide electrolytes offer great potential for analyzing various atmospheres at high temperatures. While relatively simple gas mixtures (H2O+N2, O2+N2) have been successfully studied by means of ZrO2-based sensors, the precise detection of more complex compounds represents a challenging task. In this work, we present our findings regarding the analysis of lower alkanes (CH4, C2H6, and C3H8) mixed with nitrogen as an inert gas, utilizing an amperometric ZrO2-based sensor. This sensor, serving as an electrochemical cell with a diffusion barrier, was tested at 500–600 °C to measure the limiting current, which depends on the gas composition and can be further used as a basis for calibration curves. In addition, the diffusion coefficients of the specified gas mixtures were successfully found and compared with references, confirming the applicability of the fabricated sensor for studying diffusion processes in wide concentration and temperature ranges.

SENSOR BASED METHOD TO DETECT AND MONITOR H2S GAS – A REVIEW

This paper reviews work for sensor design along with sensing characteristics (stability, sensitivity, responsetime, range of operation etc.) to detect and control the risk of manure gas (H2S gas). The comparison between sensors can be done on the basis of operating range of gas concentration and working principle and limitations of different parameters of sensor are identified. Solid state gas sensor measure intensive parameters on a successful scale and less successful in measuring concentration of gas (H2,O2,CO, CO2, methane etc). It was observed that sensing parameters can be explored for detecting H2S gas by using semiconductor metal oxide such as CuO, SnO2, ZnO, NiO, etc. Recently has been seen that CuO-based sensors have good sensing properties toward H2S gas. The alternative of metal oxide sensor is use of conductive polymer on sensitizing surface. It is reviewed that ultrafast response/recovery and high selectivity parameters are very promising when hydrogen sulphide gas sensors are fabricated using -Fe2O3 nano-ellipsoids. It also describes future aspects of these sensor based method.

Solid-state gas sensors: sensing mechanisms and materials

Solid-state gas sensors: sensing mechanisms and materials

Molecularly imprinted nanocomposites of CsPbBr3 nanocrystals: an approach towards fast and selective gas sensing of explosive taggants

Solid-state luminescent gas sensor based on CsPbBr3 NCs embedded in a molecularly imprinted polymer (MIP) with fast response and high selectivity to nitro compounds.

Mn-doped tin oxide based sensor for selective ethanol detection

Solid-state gas sensors are being highly sought out in recent years for forensic and medical applications. Throughout the years, the transduction used for these sensors has utilized both chemical composition and morphological properties. Taking Breath Alcohol Concentration (BrAC) through ethanol sensing is considered a fast and reliable way of identifying drunken drivers. Solid-state sensors allow the development of compact, cheap, and much faster apparatuses for the job. Although Tin-oxide has a sensitive response to ethanol, acetone also has almost the same sensitivity. This cross-sensitivity may cause difficulties in human breath analysis because acetone is a common component in human breath, and diabetic patients are prone to have much higher acetone concentrations than the norm. Diabetes being a common health issue today, this research solved the difficulty mentioned above, preventing false interpretations and false alarms. In this study, the effect of Manganese doping of Tin-oxide is discussed with regard to its sensitivity and cross-sensitivity as an ethanol sensor. Furthermore, design aspects of such a thin solid-state sensor with the best operating temperature, optimum Mn concentration, and choice of substrate materials to prevent undesirable thermal stresses are discussed.

Room-Temperature Mixed-Potential Type ppb-Level NO Sensors Based on K2Fe4O7 Electrolyte and Ni/Fe-MOF Sensing Electrodes.

Portable and sensitive mixed-potential type solid-state electrolyte (MPSE) gas sensors can detect exhaled biomarkers in a noninvasive and inexpensive way, which is significant for convenient disease diagnosis and saving medical resources. However, high working temperature is still one of the main bottlenecks for hindering MPSE gas sensors' applications in disease diagnosis. Here, we, for the first time, developed and fabricated new room-temperature MPSE gas sensors utilizing K2Fe4O7 electrolyte and Ni/Fe-MOF (Ni/Fe clusters are coordinated with 1,4-H2BDC) sensing electrodes (SEs) for the detection of ppb-level NO. Among different MOF SEs, the sensor attached with the Ni-MOF SE presents the highest NO sensitivities. This is attributed to a reducing oxygen reduction reaction activity and enhancing NO electrochemical catalytic reaction activity, verified by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests. In addition, the presented sensor also shows a low detection limit (20 ppb), fast response/recovery characteristic (17 s/6 s to 50 ppb NO), excellent selectivity, acceptable repeatability, and long-term stability of 34 days to NO at 25 °C and 60%RH. Simultaneously, the mechanism of humidity effect on the sensing performance was investigated by EIS and CV tests. Our work provides new insight into the development of room-temperature solid-state electrolyte gas sensors based on the mixed-potential mechanism and enlarges the potential application domain.

Comparison of CO and CO2 rf plasma treatment of SnO2 nanoparticles for gas sensing materials

CO and CO2 plasmas were used to modify SnO2 nanoparticles (NPs) to understand the role of key gas-phase species and to explore a potential route for improving these materials as solid-state gas sensors. Excited state species in both plasmas were monitored using optical emission spectroscopy and the NP were analyzed after plasma exposure with x-ray photoelectron spectroscopy. These studies reveal that in the CO2 plasma, CO2 decomposes to CO and O, leading to etching of the SnO2 lattice. Conversely, in the CO plasma, very little O is formed, leading to the deposition of a carbonaceous film on the SnO2 NP. Sensors fabricated with the CO2 modified SnO2 NP demonstrate a higher response to CO, benzene, and ethanol and improved response and recovery behavior when compared with untreated devices. CO plasma modification, however, had a detrimental effect on the gas sensing performance of this material.

Design and validation of a novel operando spectroscopy reaction chamber for chemoresistive gas sensors

This work deals with the experimentation of a new ambient chamber for the use in diffuse reflectance Fourier infrared spectroscopy studies on chemoresistive gas sensors in operando condition. This system can support the investigation of gas–solid phase reactions at the sensor's surface during its operation, providing a reliable characterization tool that can be easily reproduced, implemented and adapted for several types of gas sensing devices. A deepened investigation was carried out: design of the chamber and the coupled acquisition system with temperature and humidity monitoring, 3D modelling, fluid dynamics study via residence time distribution analysis, and temperature gradient evaluation. Then, the system was validated in the case of a SnO2 sensor exposed to hydrogen gas flow. The new developed low void-volume gas sensing system is easy to machine, to use, to maintain, and it can be employed with solid-state gas sensors with an active area of 1 mm2 and operating temperatures up to 650 °C. In order to improve and facilitate the spectra acquisition, the system is equipped with precision staging and alignment, and it is fully compatible with Harrick Scientific's diffuse reflectance accessory.

Determining humidity of nitrogen and air atmospheres by means of a protonic ceramic sensor

• An original design of a solid-state high-temperature amperometric gas sensor. • The sensor includes two electrochemical cells based on proton-conducting electrolytes. • Sc-doped barium stannate is used for the first time as the sensor’s electrolyte. The present work describes a design, fabrication, operation principle and testing of a solid-state amperometric sensor used for humidity analysis of nitrogen and air gas atmospheres. This sensor consists of two electrochemical cells (in fact, two sensors are combined into one) based on proton-conducting electrolytes, one of the cells is made of Sc-doped calcium zirconate (CaZr 0.95 Sc 0.05 O 3–δ ; CZS), while another is made of Sc-doped barium stannate (BaSn 0.75 Sc 0.25 O 3–δ ; BSS). Using two sensors in one allowed us to compare their sensing properties. The sensor was tested at 500 °C and different water vapor partial pressures (pH 2 O). The volt-ampere ( U – I ) dependencies and calibration curves (limiting current vs pH 2 O) of the fabricated sensor were obtained and analyzed. The limiting current of the BSS-based cell is reached at a lower voltage than that of the CZS-based cell. In a nitrogen-containing atmosphere, the limiting current was reached for both electrochemical cells, and it varied linearly depending on pH 2 O. In an air atmosphere, the limiting current could not be reached only for the BSS-based cell at pH 2 O values less than 0.043 atm. A possible explanation for this is proposed.

Recording the Presence of Peanibacillus larvae larvae Colonies on MYPGP Substrates Using a Multi-Sensor Array Based on Solid-State Gas Sensors.

American foulbrood is a dangerous disease of bee broods found worldwide, caused by the Paenibacillus larvae larvae L. bacterium. In an experiment, the possibility of detecting colonies of this bacterium on MYPGP substrates (which contains yeast extract, Mueller-Hinton broth, glucose, K2HPO4, sodium pyruvate, and agar) was tested using a prototype of a multi-sensor recorder of the MCA-8 sensor signal with a matrix of six semiconductors: TGS 823, TGS 826, TGS 832, TGS 2600, TGS 2602, and TGS 2603 from Figaro. Two twin prototypes of the MCA-8 measurement device, M1 and M2, were used in the study. Each prototype was attached to two laboratory test chambers: a wooden one and a polystyrene one. For the experiment, the strain used was P. l. larvae ATCC 9545, ERIC I. On MYPGP medium, often used for laboratory diagnosis of American foulbrood, this bacterium produces small, transparent, smooth, and shiny colonies. Gas samples from over culture media of one- and two-day-old foulbrood P. l. larvae (with no colonies visible to the naked eye) and from over culture media older than 2 days (with visible bacterial colonies) were examined. In addition, the air from empty chambers was tested. The measurement time was 20 min, including a 10-min testing exposure phase and a 10-min sensor regeneration phase. The results were analyzed in two variants: without baseline correction and with baseline correction. We tested 14 classifiers and found that a prototype of a multi-sensor recorder of the MCA-8 sensor signal was capable of detecting colonies of P. l. larvae on MYPGP substrate with a 97% efficiency and could distinguish between MYPGP substrates with 1–2 days of culture, and substrates with older cultures. The efficacy of copies of the prototypes M1 and M2 was shown to differ slightly. The weighted method with Canberra metrics (Canberra.811) and kNN with Canberra and Manhattan metrics (Canberra. 1nn and manhattan.1nn) proved to be the most effective classifiers.

Benefits of virtual sensors for air quality monitoring in humid conditions

The gas sensing mechanisms, response, and behaviour of a real and a virtual solid-state chemical gas sensor operating either in static or in dynamic mode have been compared. The analysis was done by exposing simultaneously both sensors to different concentrations of various volatile organic compounds diluted in dry, as well as humid, synthetic air. The results revealed similar responses and behaviours for both types of measurement modes when the sensors were exposed towards single gas compounds, but a sensitivity enhancement in measurements comprising mixtures of gases when the sensors were operated in dynamic mode. The method used is able to overcome surface saturation problems and is beneficial for applications where mixtures of gases diluted in relative humidity are present.