Chemoresistive Sensors Research Articles

Chemoresistive H2S sensor based on PANI/TiO2/CuCl2 nanocomposite impregnated conductive fabric using TOPSIS and Taguchi method

Abstract Conductive polymer/metal oxide nanocomposites have been widely used for chmoresistive gas sensors. PANI/TiO2/CuCl2 nanocomposite(PTCN) impregnated conductive fabric was prepared by in-situ synthesis method. To improve the performance of PTCN impregnated fabric for detecting H2S gas, Taguchi orthogonal array(TOA) is used to experimental design, and best values of factors affecting to the sensing performance are determined using Technique for order preference by similarity to ideal solution (TOPSIS) and Taguchi optimization method. PTCNs were charactierized by SEM, XRD, FTIR. The sensing performances of the proposed sensor such as linear detection range, sensitivity, repeatability and effect of humidity for hydrogen sulfide gas were evaluated.

Highly Durable Chemoresistive Micropatterned PdAu Hydrogen Sensors: Performance and Mechanism.

Hydrogen (H2) is a promising alternative energy source for Net-zero, but the risk of explosion requires accurate and rapid detection systems. As the use of H2 energy expands, sensors require high performance in a variety of properties. Palladium (Pd) is an attractive material for H2 detection due to its high H2 affinity and catalytic properties. However, poor stability caused by volume changes and reliability due to environmental sensitivity remain obstacles. This study proposes a micropatterned thin film of PdAu with optimized composition (Pd0.62Au0.38) as a chemoresistive sensor to overcome these issues. At room temperature, the sensor has a wide detection range of 0.0002% to 5% and a fast response time of 9.5 s. Significantly, the sensor exhibits excellent durability for repeated operation (>35 h) in 5% H2 and resistance to humidity and carbon monoxide. We also report a negative resistivity change in PdAu, which is opposite to that of Pd. Density functional theory (DFT) calculations were performed to investigate the resistance change. DFT analysis revealed that H2 penetrates specific interstitial sites, causing partial lattice compression. The lattice compression causes a decrease in electrical resistance. This work is expected to contribute to the development of high-performance H2 sensors using Pd-based alloys.

Copper Corrole Electropolymers

The electrochemical polymerization of the copper complex of 5,10,15-tris-(4-aminophenyl) corrole leads to the formation of conductive films, which have been deposited onto interdigitated electrodes to develop chemoresistive sensors. These devices are of interest because of their facile miniaturization and integration into low-cost electronic circuits. It is interesting to note that the properties of these films, such as morphology, semiconducting nature and sensitivity, can be tuned by modifying the synthetic electropolymerization protocols. This opportunity can allow the preparation of cross-selective sensors that can be integrated into miniaturized conductometric electronic nose platforms.

2D Amino-Functionalized Black Phosphorus: A New Approach to Improve Hydrogen Gas Detection Performance.

In recent years, hydrogen has gained attention as a potential solution to replace fossil fuels, thus reducing greenhouse gas emissions. The development of ever improving hydrogen sensors is a topic that is constantly under study due to concerns about the inherent risk of leaks of this gas and potential explosions. In this work, a new, long-term, stable phosphorene-based sensor was developed for hydrogen detection. A simple functionalization of phosphorene using urea was employed to synthesize an air-stable material, subsequently used to prepare films for gas sensing applications, via the drop casting method. The material was deeply characterized by different techniques (scanning electron microscopy, X-ray diffraction, X-ray photoelectron, and Raman spectroscopy), and the stability of the material in a noninert atmosphere was evaluated. The phosphorene-based sensor exhibited high sensitivity (up to 700 ppm) and selectivity toward hydrogen at room temperature, as well as long-term stability over five months under ambient conditions. To gain further insight into the gas sensing mechanism over the surface, we employed a dedicated apparatus, namely operando diffuse reflectance infrared Fourier transform, by exposing the chemoresistive sensor to hydrogen gas under dry air conditions.

Micrometric thermal electronic nose able to detect and quantify individual gases in a mixture

Recent urbanization and environmental problems urge for networks of sensors that can monitor air quality. Small, inexpensive, and smart sensors are one of the key components enabling the realization of such networks. Chemoresistive sensors are the ideal candidate, but they greatly lack selectivity, and for this reason, they are usually combined in arrays to create electronic noses, whose dimensions, however, make them not miniaturizable and cannot be integrated into portable devices. To overcome this inconvenience, we present a thermal electronic nose consisting of identical resistive sensors working at different temperatures so that the whole device is simple to make and tiny. The device contains two sensor arrays based on tin oxide nanowires decorated with Ag and Pt nanoparticles, respectively. The five sensors in each array are identical, but their response is differentiated by different temperatures locally generated by an on-chip integrated heater. This innovative approach allows the tiny array of five sensors together with the integrated heater to occupy only approximately 50 × 200 μm2 and consume only 120 μW. The tiny and portable device can estimate the concentration of H2 and NH3 in a mixture with a root mean square error of 6.1 ppm and 13.3 ppm, respectively, and it still works well after two months. The performance analysis of the double partial least squares regression used for concentration estimation also allows for feedback on which sensors are the most sensitive to which gas so that the electronic nose can be engineered for specific applications using the most suitable sensors. The size of the thermal electronic nose allows it to be integrated into portable and wearable devices, and its performance makes it suitable for any gas detection application. For example, a smartphone with an integrated sensor could carry out breath analysis and act as medical pre-screening or be used to evaluate the freshness of agri-food products in a rapid and non-invasive way.

Novel Chemoresistive Sensors for Indoor CO2 Monitoring: Validation in an Operational Environment

Novel Chemoresistive Sensors for Indoor CO₂ Monitoring: Validation in an Operational Environment

Advanced Nanostructured All‐Waterborne Thiol‐Ene/Reduced Graphene Oxide Humidity Sensors with Outstanding Selectivity

AbstractThe current‐state of polymer‐based humidity sensors faces numerous limitations, including energy‐costly synthesis, low sensitivity, and slow response times. This study presents innovative approach to overcome these challenges, based on a robust all‐water‐borne in situ miniemulsion polymerization. The use of water throughout the entire process mitigates the negative environmental impact. Thiol‐ene polymers reinforced with reduced graphene oxide (rGO) with concentrations ranging from 0.2–1.0 wt% are selected to fabricate these chemoresistive sensors. The selected thiol‐enes present high hydrophobicity and a semicrystalline nature, suggesting resistance to early delamination even under prolonged exposure to humidity. Incorporating rGO not only imparts electrical conductivity but also enhances mechanical and water resistance of the composite films. The 0.6% rGO composite exhibits optimal resistance for humidity sensing, demonstrating rapid and consistent responses across three exposure cycles to water vapor concentrations ranging 800–5000 ppm. Moreover, the sensor exhibits remarkable selectivity toward water vapors over these of toluene, propanol, and 4‐methyl‐2‐pentanol, attributed to the high surface hydrophilicity and inherent porosity of the waterborne film, and network structuring of rGO platelets within the matrix. In summary, this study pioneers a novel approach to polymer‐based humidity sensing, addressing key limitations while offering enhanced sensitivity, rapid response times, and superior selectivity.

Enhanced visible light-activated gas sensing properties of nanoporous copper oxide thin films

Metal oxide gas sensors are popular chemoresistive sensors. They are used for numerous tasks, including environmental and safety monitoring. Some gas-sensing materials exhibit photo-induced properties that can be utilized for enhanced gas detection by modifying the sensor selectivity and sensitivity when illuminated by light. Here, we present the gas sensing characteristics of highly nanoporous Cu2O thin films towards both electrophilic (NO2) and nucleophilic (C2H5OH, NH3) gas molecules under ambient temperature and modulated by visible light illumination of different colors (red: 632 nm, green: 530 nm, blue: 468 nm). Cu2O films were fabricated by reactive advanced gas deposition (AGD) technology. The surface and structural analysis of the samples confirm the deposition of nanoporous thin films of mixed copper oxide phases. The gas sensing property of Cu2O exhibited expected p-type semiconductor behavior upon electrophilic and nucleophilic gas exposures. Our results show that visible light illumination provides enhanced sensor response.

Metal Oxide-Based Sensors for Ecological Monitoring: Progress and Perspectives

This paper aims to provide a large coverage of recent developments regarding environmental monitoring using metal oxide-based sensors. Particular attention is given to the detection of gases such as H2, COx, SOx, NOx, and CH4. The developments and analyses of the design of sensors and types of metal oxide sensing materials are emphasized. The sensing mechanisms and peculiarities of metal oxides used in chemoresistive sensors are provided. The main parameters that affect the sensitivity and selectivity of metal oxide sensors are indicated and their significance to the sensor signal is analyzed. Modern data processing algorithms, employed to optimize the measurement process and processing of the sensor signal, are considered. The existing sensor arrays/e-nose systems for environmental monitoring are summarized, and future prospects and challenges encountered with metal oxide-based sensor arrays are highlighted.

Fabrication of Highly Sensitive YCeO Chemo-resistive Gas Sensor for Selective Detection of CO2

A room-temperature-operated CO2 gas sensor based on YCeO nanocomposite was effectively prepared by the simple hydrothermal technique to detect low traces of CO2 (50–250 ppm). The YCeO granular morphological features were observed using field-emission scanning electron microscopy, which confirmed successful fabrication of nanocomposite of Y2O3 and CeO2. X-ray diffraction of YCeO showed the Cubic structure of space group Fm3m having density 6.74 gmcm−3. Rietveld refinement was performed for the analysis of complete crystal structural property. Surface porosity and specific surface area were observed by Brunnauer-Emmet Teller analysis. Optical properties were observed using UV-Visible spectroscopy. The band gap, optical conductivity, and refractive index calculated were 3.44 eV, 2.63 × 106, and 0.1164, respectively. Fourier transform infrared spectroscopy was done to analyze the functional and elastic properties of as-prepared nanomaterial. The highest sensor response recorded was 2.14. The response and recovery time at 50 ppm observed were 75.6 and 107.3 s, respectively. The YCeO chemo-resistive sensor confirmed long-term stability and selectivity to CO2 as compared to other gases viz. LPG, NH3, CH4, H2S, NO2 and H2. The relative humidity exposure was also performed at 15, 55 and 95% RH, in which it was confirmed that the sensor would give best response at mid humidity level i.e. 55 %RH. Sensing characteristics curve of YCeO nanocomposite at different temperature (30 °C–90 °C) at 50 ppm confirmed that YCeO sensor performed excellent at room temperature. This report unlocks an innovative opening for the fabrication of sensing devices that are room-temperature-operatable, highly sensitive and selective for quick detection of CO2 gas for its commercialization.

Gas-sensing performance of SnO2-based chemoresistive sensors after irradiation with alpha particles and gamma-rays

Gas-sensing performance of SnO2-based chemoresistive sensors after irradiation with alpha particles and gamma-rays

Biphenyl-rGO composite room temperature gas sensor for enhanced amine sensing

Amines, which are classified as volatile organic compounds (VOCs), serve a variety of purposes in the fields of environmental monitoring, food safety, and healthcare diagnosis. The present technique for detecting amine levels involves sophisticated setups and bulky equipment. Here. In this study, a chemoresistive gas sensor is developed that is cost-effective and easy to operate at room temperature (RT). The sensor is designed specifically for the detection of Ammonia, dimethylamine (DMA), trimethylamine (TMA), and total volatile basic nitrogen (TVB-N). Using biphenyl-reduced graphene oxide (B-rGO) composite gas sensors effectively addresses the issues of low sensitivity-selectivity and long-term instability commonly observed in conventional amine sensors. B-rGO sensor produced sensitivity of ∼3500 and selectivity above 30 for TVB-N sensing. The sensor is stable for temperature fluctuations below 50 °C and shows stable sensing response for period of over 3 months. A Chemoresistive B-rGO sensor was developed using an ultrasonic spray deposition system with optimized flow rate of 50 mL/h. Rapid evaporation of solvent using hot plate has resulted in unique morphology for B-rGO film sensors. The highest sensitivity, ∼836, is obtained for 100 ppm of ammonia with ammonia > DMA > TMA as a sensitivity order. B-rGO showed almost seven times higher amine sensitivity than rGO which highlights the importance of biphenyl in the B-rGO composite. Sensor calibration curve has been presented in the study to understand change in the sensitivity of sensor with increasing analyte gas concentration. The calibration curve has an average R-squared value of 0.98.

A Review on Metal Oxide Semiconductor-Based Chemo-Resistive Ethylene Sensors for Agricultural Applications

Ethylene, an important phytohormone, significantly influences plant growth and the ripeness of fruits and vegetables. During the transportation and storage of agricultural products, excessive ethylene can lead to economic losses due to rapid deterioration. Metal oxide semiconductor (MOS)-based chemo-resistive sensors are a promising technology for the detection of ethylene due to their low cost, high sensitivity, portability, etc. This review comprehensively summarizes the materials, fabrications, agricultural applications, and sensing mechanisms of these sensors. Moreover, the current challenges are highlighted and the potential solutions are proposed.

Flicker Noise in Resistive Gas Sensors-Measurement Setups and Applications for Enhanced Gas Sensing.

We discuss the implementation challenges of gas sensing systems based on low-frequency noise measurements on chemoresistive sensors. Resistance fluctuations in various gas sensing materials, in a frequency range typically up to a few kHz, can enhance gas sensing by considering its intensity and the slope of power spectral density. The issues of low-frequency noise measurements in resistive gas sensors, specifically in two-dimensional materials exhibiting gas-sensing properties, are considered. We present measurement setups and noise-processing methods for gas detection. The chemoresistive sensors show various DC resistances requiring different flicker noise measurement approaches. Separate noise measurement setups are used for resistances up to a few hundred kΩ and for resistances with much higher values. Noise measurements in highly resistive materials (e.g., MoS2, WS2, and ZrS3) are prone to external interferences but can be modulated using temperature or light irradiation for enhanced sensing. Therefore, such materials are of considerable interest for gas sensing.

Graphene and metal-organic framework hybrids for high-performance sensors for lung cancer biomarker detection supported by machine learning augmentation.

Conventional diagnostic methods for lung cancer, based on breath analysis using gas chromatography and mass spectrometry, have limitations for fast screening due to their limited availability, operational complexity, and high cost. As potential replacement, among several low-cost and portable methods, chemoresistive sensors for the detection of volatile organic compounds (VOCs) that represent biomarkers of lung cancer were explored as promising solutions, which unfortunately still face challenges. To address the key problems of these sensors, such as low sensitivity, high response time, and poor selectivity, this study presents the design of new chemoresistive sensors based on hybridised porous zeolitic imidazolate (ZIF-8) based metal-organic frameworks (MOFs) and laser-scribed graphene (LSG) structures, inspired by the architecture of the human lung. The sensing performance of the fabricated ZIF-8@LSG hybrid sensors was characterised using four dominant VOC biomarkers, including acetone, ethanol, methanol, and formaldehyde, which are identified as metabolomic signatures in lung cancer patients' exhaled breath. The results using simulated breath samples showed that the sensors exhibited excellent performance for a set of these biomarkers, including fast response (2-3 seconds), a wide detection range (0.8 ppm to 50 ppm), a low detection limit (0.8 ppm), and high selectivity, all obtained at room temperature. Intelligent machine learning (ML) recognition using the multilayer perceptron (MLP)-based classification algorithm was further employed to enhance the capability of these sensors, achieving an exceptional accuracy (approximately 96.5%) for the four targeted VOCs over the tested range (0.8-10 ppm). The developed hybridised nanomaterials, combined with the ML methodology, showcase robust identification of lung cancer biomarkers in simulated breath samples containing multiple biomarkers and a promising solution for their further improvements toward practical applications.

Detection of sulfur mustard simulant by trisaryl phosphoric triamide-based resin using a quartz crystal microbalance sensor.

Chemical warfare agents (CWAs) pose a persistent threat to human safety, and bis(2-chloroethyl) sulfide, or sulfur mustard (SM) is one of the most dangerous substances and is able to cause serious harm. Detecting SM gas is vital, but current methods have high-temperature requirements and limited selectivity, mainly because of the lack of CWA receptor development, and this makes them challenging to use. To address this issue, we present a trisaryl phosphoric triamide-based resin receptor that preferentially interacts with a SM simulant 2-chloroethyl ethyl sulfide (2-CEES) through dipole interactions. The receptor was synthesized through a facile process using an amine and a triethyl phosphate and the properties of its coating were enhanced using epoxy chemistry. The receptor's superior triamide structure was evaluated using a quartz crystal microbalance and reactivity was confirmed by observing the variations in reactivity according to the number of phosphoramides. The receptor showed better reactivity to 2-CEES vapor than to the known poly(epichlorohydrin) and showed selectivity to other volatile organic compounds. Moreover, its durability was evident even 30 days post-coating. The applicability of this receptor extends to array sensors, sound acoustic wave sensors, and chemo-resistive and chemo-capacitive sensors, and it promises advances in chemical warfare agent detection.

AuNP-decorated textile as chemo resistive sensor for acetone detection

AuNP-decorated textile as chemo resistive sensor for acetone detection

Sensing nature's alarm: SnO2/MXene gas sensor unveils methyl jasmonate signatures of plant insect stress.

The incorporation of artificial intelligence into agriculture presents challenges, particularly due to hardware limitations, especially in sensors. Currently, pest detection relies heavily on manual scouting by humans. Therefore, the objective of this study is to create a chemoresistive sensor that enables early identification of the characteristic volatile compound, viz., methyl jasmonate, released during pest infestations. Given the lower reactivity of esters, we have fine-tuned a composite consisting of SnO2 nanoparticles and 2D-MXene sheets to enhance adsorption and selective oxidation, resulting in heightened sensitivity. The optimized composite demonstrated a notable response even at concentrations as low as 120 ppb, successfully confirming pest infestations in tomato crops.

Mechanically robust and conductive zwitter ionic polymer coated electrospun nanofibrous electrolyte membranes for wireless human motion detection and capacitor applications

To address the limitations of poor ionic conductivity, low toughness, and high mass ratios in hydrogel-based electrolytes for flexible energy storage and wearable devices, here in a simple synthesis method of poly(ionic liquids) (PILs) based electrolyte membrane was developed. Briefly, PILs were utilized to coat electrospun PVDF-HFP nanofibrous membranes, resulting in ionically conducting composite electrolyte membranes (CPEMs) with enhanced physio-chemical properties. The obtained CPEMs exhibited an ionic conductivity of 0.056 S/m, along with a high tensile strength of 5.06 MPa and elongation to break of 156 %. Furthermore, we utilized these CPEMs as the electrolyte in symmetric capacitors by sandwiching them between carbon nanotube (CNT) coated Ni-foams. The resulting capacitors demonstrated a specific capacitance of 170F/g, an energy density of 53.41 Wh/kg, and a power density of 108.9 W/kg at an applied current of 1 mA. The suitability of these CPEMs as chemo-resistive sensors was investigated by attaching them to different body parts and monitoring changes in resistance during physical motion. The results demonstrated that the CPEMs exhibited effective gauge factors ranging from 1.85 to 6.44 and could detect movements up to 1 % strains.

Elevating selective ethanol detection based on unlocking the potential of accordion structured MXene

Two-dimensional (2D) transition-metal carbides (Ti3C2Tx) MXene have received much attention due to their exciting prospects for application in gas sensing. Large surface area, metallic conductivity, and the functionalization potential all are key characteristics of MXene. These materials have optimum gas selectivity and responsiveness among 2D materials. By using HF etching, we developed exfoliated MXene from MAX phase of Ti3AlC2. The William-Hall (W-H) plot estimated the size of the crystallite to be 7.95 nm. The calculated optical band gap was found 1.53 eV. The almost disappearance of aluminum (Al) layers was confirmed by the XRD(X-ray diffraction) peak shift, EDS and XPS analysis and the accordion-like morphology confirmed by FESEM images. The specific surface area of synthesized MXene was found to be 39.00 m2g-1, while the pore volume of MXene was estimated as 0.0755852 cm3g-1 and the pore diameter was evaluated as 3.42782 nm. The experimental findings demonstrate the fact that Ti3C2Tx incorporation improves the sensitivity, the repeatability, and the selectivity of chemo-resistive sensors that are sensitive to VOCs (volatile organic compounds) such as acetone, ethanol, methanol, propanol, and hexane. The fabricated MXene based sensor was tested under exposure of aforementioned VOCs at 600 ppm. The initial finding illustrates that among these, ethanol is the most sensitive VOC. The fabricated Ti3C2Tx sensor yielded response (%) at the concentrations of 50, 100, 200, 300, 400 and 500 ppm as 1.78, 2.63, 3.42, 4.28, 5.05, and 5.47%, respectively under purging ethanol. The maximum response at room temperature (RT) operable ethanol sensor was calculated as 5.65% at 600 ppm under 40% of relative humidity (RH). The outcomes demonstrate rapid responses/recovery of 5s and 8s, respectively.