Ultrasensitive Gas Sensor Research Articles

An ultra-sensitive gas sensor based on a two-dimensional manganese porphyrin monolayer.

The development of highly sensitive, low-power consuming, stable and recyclable gas sensing devices at room temperature has become an important solution for environmental safety detection. Utilizing a two-dimensional metalloporphyrin monolayer for gas sensing is appealing due to its large specific surface area and high surface activity. A two-dimensional manganese porphyrin monolayer (2DMnPr) is selected from 2D metalloporphyrins with 3d metal centers due to its semi-metallicity to explore its gas sensing properties. Using first-principles calculations, we systematically investigate the electronic structures and adsorption characteristics of gas molecules with toxicity and greenhouse effect on the surface of 2DMnPr, including H2S, CO, CO2, SO2, NO and NO2. The strength of the interaction and charge transfer between the 2DMnPr surface and the adsorbed molecules have a direct effect on the electronic properties and the sensing properties of the adsorbent surface. The sensing performance of the 2DMnPr adsorbent is evaluated via two observable parameters: work function and electrical conductivity. The work functions of 2DMnPr after the adsorption of CO, SO2, NO and NO2 gas molecules increase by different degrees depending on the charge transfer, and those of the H2S and CO2 cases decrease. In our simulation, adsorption of CO, SO2, NO and NO2 gas molecules affects the electronic properties of 2DMnPr markedly, and current-voltage characteristics within a low bias range uncover the superior sensitivity of the conductivity of the 2DMnPr monolayer to these molecules. Besides, the sensing performance is demonstrated to be stable under strain and at room temperature. The desorption time of a gas is positively related to its adsorption energy. The recovery time of CO is predicted to be short enough to realize sustainable detection at room temperature, and the SO2, NO and NO2 gases can also be desorbed at higher temperatures. These results demonstrate that 2DMnPr enables the sensitive detection of these gases and predict the potential application of 2DMnPr as an ultra-sensitive, low-power, stable and recyclable gas sensor at room temperature.

Ultrasensitive and light-activated NO2 gas sensor based on networked MoS2/ZnO nanohybrid with adsorption/desorption kinetics study

In this work, a high-performance room temperature NO2 chemoresistive gas sensor is fabricated using a MoS2/ZnO nanohybrid. The nanohybrid is synthesized by drop-casting liquid exfoliated MoS2 nanosheets on ZnO nanorods. The uniform network-like distribution of MoS2 nanosheets on the nanorods is confirmed by various characterization techniques. Under UV-activation, the nanohybrid sensor exhibits remarkable responses of 91% and 2310% at 5 and 500 ppb NO2, respectively. In addition, full recovery to the base resistance is observed in each sensing cycle. The low concentration sensitivity is 0.135 ppb−1 and the lowest detection limit is estimated to be around 0.2 ppb. These two values are superior when compared with other reports. The adsorption/desorption kinetics has been studied in detail using the Langmuir adsorption model. The saturated response, the adsorption, and the desorption constant are determined to be 2744%, 3.52 × 10–5 ppb−1 s−1, and 3.50 × 10–3 s−1, respectively. The outstanding performance of the sensor can be attributed to the synergetic effects of MoS2 and ZnO including creation of abundant adsorption sites and fast charge carrier migration.

Highly sensitive H2 sensor based on PdO-decorated WO3 nanospindle p-n heterostructure

A highly sensitive H2 gas sensor based on n-WO3/p-PdO heterostructure has been fabricated. Using hydrothermal method, through tuning the pH value of the solution, WO3 nanospindles were synthesized. SEM reveals its uniform morphology; XRD result shows its high crystal quality; N2 adsorption/desorption result proves its relatively high specific surface area. Through first soaking then calcinating method, PdO was loaded on the surface of WO3 nanospindles. XPS and HRTEM together have proved the fabrication of the heterostructure between n-WO3/p-PdO. The gas sensing device was fabricated by coating the PdO loaded WO3 paste on a ceramic substrate with silver palladium interdigital electrodes. After loaded into the test chamber, preheated to the required temperature and injecting a certain amount of H2, the sensing procedure was done. With optimal ratio of loaded PdO to WO3 (3 at%), the sensor shows the best gas sensitivity at 150 °C. To 1, 5, 10, 20 and 50 ppm H2, the sensor shows the response values (Ra/Rg) of 1.3, 7, 23, 37 and 76, in the response time of 9s, 8s, 5s, 3s and 1s, respectively. The quasi-one dimensional (QOD) character of WO3 nanospindle, the well-performance heterostructure between WO3 and PdO and the optimal ratio of loaded PdO to WO3 together make the sensor own strong sensing ability towards H2. The such well-performance H2 gas sensor based on n-WO3/p-PdO heterostructure reminds us that the WO3/PdO system has supplied a good material platform to explore the fabrication of ultrasensitive and stable H2 gas sensor.

Multifunctional sodium alginate fabric based on reduced graphene oxide and polypyrrole for wearable closed-loop point-of-care application

Sodium alginate (SA) fabrics decorated with reduced graphene oxide (rGO) and polypyrrole (PPy) serving as multifunctional materials are prepared by thermal-press reduction and in-situ polymerization. The superior conductivity (0.17 kΩ·sq−1) of SA/rGO/PPy composite fabric is optimized through L9(34) orthogonal experimental design. Microstructures of the resultant SA/rGO/PPy composite fabric are investigated by field emission -scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction measurement, respectively. It is found that SA/rGO/PPy composite fabric possesses not only excellent thermal stability but also mechanical durability. The results of NH3 gas experiments indicate that SA/rGO/PPy composite fabric exhibits reliable linearity of concentration (2–16 ppm) dependency, unique repeatability, a high sensing response (10.7%) at low detection limit of 2 ppm and admirable selectivity. Moreover, SA/rGO/PPy composite fabric acting as a heater can reach to approximately 40–90 ℃ at low voltage of 3 V to 9 V. Hence, the optimum SA/rGO/PPy composite fabric is supposed to be used as ultrasensitive NH3 gas sensor and wearable heater for nephropathy diagnosis purpose and thermo-responsive drug deliver in point-of-care (POC) application to develop a closed-loop treatment.

UV-enhanced room-temperature ultrasensitive NO gas sensor with vertical channel nano-porous organic diodes

In this work, we successfully proposed an organic semiconductor gas sensor on vertical channel design to exhibit an ultra-sensitive response to nitric oxide gas (10 ppb) at room temperature. The effect of ultra-violet (UV) irradiation (λ =365 nm) on sensing performance of solution processed vertical organic diode (VOD) has been investigated. After implementing a simple and low-cost UV treatment, the sensing response of PBDTTT-C-T based NO sensor is significantly enhanced from 93 % to 233 % at 1 ppm. In addition, we also introduced a new strategy to tune the selectivity of organic gas sensors by using photochromic molecule and organic semiconductor blends. With the 1 Wt% spiropyran dopant, the sensor response to ammonia can be considerably suppressed, hence the response ratio between NO and ammonia can be improved from 2.9 to 16.0, indicating an improved selectivity. The proposed ultrasensitive and selective NO gas sensor have great potential for exhaled breath detection (asthma patients) and environmental monitoring.

Ultra-sensitive and selective p-xylene gas sensor at low operating temperature utilizing Zn doped CuO nanoplatelets: Insignificant vestiges of oxygen vacancies

p-xylene is a harmful volatile organic compound that needs to be tested for indoor air quality detection. We report on the sensing characteristics of CuO and Zn doped CuO nanoplatelets of various concentrations that were prepared by hydrothermal synthesis, against nine different gases. These CuO and Zn based nanoplatelets were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, photoluminescence emission and vibrating sample magnetometer measurements. CuO and 0.1 at. % Zn doped CuO samples were most sensitive and selective to p-xylene gas with relatively high responses (Ra/Rg ratio) of about 42 and 53 at an operating temperature of 150 °C, respectively. These responses were about six times higher compared to the other 8 tested interfering gases. All these samples further exhibited a paramagnetic behaviour at room temperature, due to small traces of point defects, such as oxygen vacancies. Both these sensor materials did not show green luminescence at room temperature that is normally associated with oxygen vacancies. However, temperature dependent photoluminescence (PL) measurements for the 0.1 at. % Zn doped CuO showed broad visible emission, including green luminescence, which increased with temperature up to 150 °C and coincided with the gas sensing temperature. The pure CuO, however, showed a rapid quenching in PL emission with an increase in the temperature up to 150 °C. Nevertheless, both pure CuO and 0.1 at. % Zn doped CuO based sensors were highly sensitive to the p-xylene gas. The mechanism associated to the xylene superior sensing was considered in terms of point defects and surface area as active sites for adsorption of gas molecules.

Ultrasensitive xylene gas sensor based on flower-like SnO2/Co3O4 nanorods composites prepared by facile two-step synthesis method

Xylene is a volatile organic compound which is harmful to the human health and requires precise detection. The detection of xylene by an oxide semiconductor gas sensor is an important research direction. In this work, Co3O4 decorated flower-like SnO2 nanorods (SnO2/Co3O4 NRs) were synthesized by a simple and effective two-step method. The SnO2/Co3O4 NRs show high xylene response (Rg/Ra = 47.8 for 100 ppm) and selectivity at the operating temperature of 280 °C, and exhibit high stability in continuous testing. The resulting SnO2/Co3O4 NRs nanocomposites show superior sensing performance towards xylene in comparison with pure SnO2 nanorods. The remarkable enhancement in the gas-sensing properties of SnO2/Co3O4 NRs are attributed to larger specific surface area and the formation of p–n heterojunction between Co3O4 and SnO2. These results demonstrate that particular nanostructures and synergistic effect of SnO2 and Co3O4 enable gas sensors to selectively detect xylene.

Ultrahigh sensitive gas sensors based on slotted photonic wire-based structures including optical microcavities

In this paper, we investigated two-dimensional (2D) and three-dimensional (3D) finite element method (FEM) simulations to provide ultrasensitive gas sensors based on silicon-on-insulator (SOI) slotted photonic wire structures in the mid-IR spectral region, tuned for the wavelength 3.392 $$\upmu \hbox {m}$$. The proposed optical microstructures have the ability to detect methane gas in the environment in addition to sensing the gas flux from the hole/slot regions with a very high sensitivity ($${S} = 2.97$$) through a very high confinement of the electric field in the photonic wire slot region that leads to an increase in the interaction of light with gas. To further boost the sensitivity of the SOI slotted photonic wire structure to the methane gas, we designed an optical microcavity in the photonic crystal (PhC) slotted structure. This microcavity can sense the smallest methane gas level $$(0.36062\,\upmu \hbox {m}^{2})$$ with high sensitivity ($${S}= 27.45$$), by means of strengthening the high-quality factor cavity mode and reduction of effective modal volumes. In addition, the ultra-wide bandgap ($$1.9\,\upmu \hbox {m}$$) obtained from Bragg mirrors of the simulated microcavity structures can facilitate us to extend the sensing in a wide range of wavelengths.

Ultrasensitive and low temperature gas sensor based on electrospun organic-inorganic nanofibers

Abstract Organic-inorganic hybrid material is one of the most promising materials for high performance gas sensors due to its improved properties like high sensitivity, selectivity, fast response time, flexibility and low power consumption. This work presents ultrasensitive, selective and low operating temperature H2S gas sensor. It is based on metal-oxide nanoparticles (NPs) embedded in organic semiconductor polymeric nanofibrous (NFs) membrane containing an ionic liquid (IL). In this context, high surface area Tungsten(VI) oxide- Polyvinyl alcohol (WO3-PVA) nanofibrous composite sensor material with average diameter of 130 ± 20 nm were synthesized with controlled morphology and interconnectivity through an electrospinning technique. The obtained WO3 NPs-containing PVA nanofibrous sensing material was evaluated for its ability as a potential sensor for H2S gas at different operating temperatures and gas concentrations. Results demonstrated that the fabricated sensor is ultrasensitive and selective for H2S gas and exhibit an excellent reproducibility, and long-term stability. Furthermore, the sensor showed adequate response in a humid environment. It was also shown that nanofibers' membrane porosity and thickness control the sensing performance. The optimum operating temperature of 40°C with a detection threshold as low as 100 ppb with a response time of 16.37 ± 1.42 s were achieved. This combined high sensitivity, fast response time and low operating temperature (low-power consumption) provides clear evidence of the sensor's potential to outperform existing devices, which could pave the way for a commercial exploitation.

Sensitivity Enhancement of Ammonia Gas Sensor Based on Hydrothermally Synthesized rGO/WO3 Nanocomposites

An ultrasensitive ammonia gas sensor based on hydrothermally synthesized rGO/WO3 nanocomposite with interdigitated chromium electrode has been fabricated. Device properties such as structural, morphological, optical, and electrical were analyzed and reported. A correlation between stability and performance of the device with electrical properties has been established. Sensor shows excellent selectivity and sensitivity towards ammonia detection, even at lower gas concentration and low operating temperature. At room temperature, the sensor depicts the sensing response 4.35 with 13/20 sec response/recovery time for 10 PPM NH3 gas concentration. Although the best sensing performance has been obtained for 150 °C operating temperature. For 10 PPM and 100 PPM NH3 gas concentration, we found sensor response 10.89 and 27.7 with 11/17 and 7/19 sec response/recovery time. The sensor has been tested for different period/interval of time and found that the proposed nanocomposite has excellent stability and reproducibility thus can be utilized for various gas sensing applications.

Ultra-sensitive ethanol gas sensors based on nanosheet-assembled hierarchical ZnO-In2O3 heterostructures

Developing efficient sensing materials with super sensitivity and selectivity is imperative to fabricate high-performance gas sensors for satisfying future needs. Herein, we report the preparation of ultrathin nanosheet-assembled 3D hierarchical ZnO/In2O3 heterostructures for the sensitive and selective detection of ethanol by sintering the 3D hierarchical Zn/In glycerolate precursors consisting of ultrathin nanosheets synthesized through a facile solvothermal method. The obtained ZnO/In2O3 heterostructures were carefully characterized by XRD, SEM, HRTEM, BET and XPS. The results showed that the 20%ZnO/In2O3 heterostructure is built up by many ultrathin nanosheets composed of intimately connected ZnO and In2O3 nanoparticles and have a specific surface area as high as 137.1 m2 g−1. Because of the unique hierarchical structure, abundant mesoporous and formation of ZnO-In2O3 n-n heterojunctions, the 20%ZnO/In2O3 heterostructure based sensor was ultra-sensitive to ethanol gas at 240 °C and exhibited a response as high as 170 toward 50 ppm of ethanol, which is about 3.3 times higher than that of pure In2O3 based sensor. Moreover, the sensor based on 20%ZnO/In2O3 heterostructure has virtues of excellent selectivity, good long-term stability and moderate response and recovery speed (35/46 s) toward ethanol. Therefore, the ultrathin nanosheet-assembled 3D hierarchical heterostructures are promising materials for fabricating high-performance gas sensors.

Na-Doped ZnO and RGO Composite-Based Flexible Acetone Gas Sensor Operated in Room Temperature

Real-time health monitoring is important in disease prediction, prevention, and early treatment. In this study, based on Na-doped ZnO/reduced graphene oxide (RGO) heterojunction, an ultrasensitive flexible room temperature gas sensor was developed for lung cancer surveillance diagnosis. The sensing material was synthesized using a simple solution route. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy were carried out to investigate the structure and chemical properties. The fabricated material has a surface-to-volume ratio, which was important to the sensing property. The gas-sensing performance was measured from 5 ppm to 200 ppm at room temperature (25 °). The proposed sensor demonstrated fast response and recovery time, as well as great repeatability and long-term stability. Furthermore, it exhibited mechanical robustness, and can be bent to different angles with almost no resistance change. Moreover, performance investigation at low acetone concentrations (0.2 ppm to 1.0 ppm) revealed its capability of distinguishing acetone gas as low as 0.2 ppm, with good linearity under different acetone concentration. As such, the developed sensor could provide a promising basis for disease monitoring through detecting the concentration of acetone gas exhaled by human.

Ultra-sensitive NO2 gas sensors based on single-wall carbon nanotube field effect transistors: Monitoring from ppm to ppb level

Owing to their sensitive chemical-to-electrical transducer capabilities and compatibility with device miniaturization and low operation temperature, single-walled carbon nanotube field-effect transistor (SWCNT-FET) represents an attractive platform to provide solutions in the gas sensing field. In this work, SWCNT-FETs were fabricated and their performances for detecting low NO2 concentrations were evaluated. Outstanding devices response was obtained, which was shown to follow a 2 power law dependence between the response and the NO2 concentration in the range of 100 ppb up to 10 ppm. Such ultra-high response is attributed to an enhancement of the Schottky barrier modulation triggered by the specific device configuration. The device configuration is based on individual semiconducting SWCNTs directly connecting the interdigitated Source-Drain electrodes. To the best of our knowledge, the results reported here correspond to the most sensitive device among the devices based on non-functionalized carbon materials and operational at low temperatures. Furthermore, the obtained results are supported by a deep SWCNT characterization, and the changes in Schottky barrier's height induced by the presence of gas molecules are estimated and discussed. Overall, the present reported results provide useful information for establishing a robust process for the fabrication of the next generation of CNT based gas-sensing devices.

Ultrasensitive and Selective Gas Sensor Based on a Channel Plasmonic Structure with an Enormous Hot Spot Region.

We present experimental and theoretical studies of a metamaterial-based plasmonic structure to build a plasmonic-molecular coupling detection system. High molecular sensitivity is realized only when molecules are located in the vicinity of the enhanced field (hot spot region); thus, introducing target molecules in the hot spot region to maximize plasmonic-molecular coupling is crucial to developing the sensing technology. We design a metamaterial consisting of a vertically oriented metal insulator metal (MIM) structure with a 25 nm channel sandwiched between two metal films, which enables the delivery of molecules into the large ravinelike hot spot region, offering an ultrasensitive platform for molecular sensing. This metamaterial is applied to carbon dioxide and butane detection. We design the structure to exhibit resonances at 4033 and 2945 cm-1, which overlap with the C═O and -CH2 vibration modes, respectively. The mutual coupling of these two resonance modes creates a Fano resonance, and their distinct peaks are clearly observed in the corresponding transmission dips. In addition, owing to its small footprint, such a vertical-oriented MIM structure enables us to increase the integration density and allows the detection of a 20 ppm concentration with negligible background noise and high selectivity in the mid-infrared region.

Ultrasensitive NO Gas Sensor Based on the Graphene Oxide-Coated Long-Period Fiber Grating.

An ultrasensitive nitric oxide (NO) gas sensor based on the graphene oxide (GO)-coated long-period fiber grating (LPFG) was constructed successfully because of its excellent sensitivity to the surrounding refractive index (SRI) change. The surface morphology and structure of GO coated on LPFG were characterized by the scanning electron microscope (SEM), scanning probe microscope (SPM), and Raman spectroscopy, respectively. The adsorption principle of NO molecules by GO was calculated in detail by density functional theory (DFT) and further characterized by Fourier transform infrared spectrometry (FT-TR) and X-ray photoelectron spectroscopy (XPS). Our studies demonstrate that the adsorption principle of NO molecules by GO was the combined effect of physical adsorption and chemical adsorption because of the formation of C-N bonds between GO and NO and the oxidization of NO to NO2. The NO sensor exhibits excellent sensing performance in the NO concentration range of 0 to 400 ppm.

Ultrasensitive NH3 Gas Sensor Based on Au/ZnO/n-Si Heterojunction Schottky Diode

An ultrasensitive ammonia gas sensor based on Au/ZnO/n-Si heterojunction Schottky diode has been fabricated by using sputtering system and photolithography. Device properties such as structural, morphological, optical, and electrical were analyzed and reported. Based on material parameters, the correlation between the optical and structural properties with gas sensing behavior has been discussed. The best sensing performance has been obtained for 150 °C operating temperature. For 10- and 50-ppm NH3 gas concentration, we have found sensor response 39.2(%) and 75(%) with 23/43 and 18/53 s response/recovery time. The ${I}-{V}$ characteristics with device parameters of the diode have been investigated in the different period/interval of time (20 months) and found that the proposed Schottky diode has excellent stability thus can be utilized as gas sensing electronic devices. A correlation between the stability and performance of the proposed device with electrical properties has also been established.

Proposal of two tangent air hole structure for higher sensitivity gas sensor

One-dimensional photonic crystal (1D PhC) cavities are used as ultrasensitive gas sensors due to their high sensitivity to changes in the surrounding environment. One of the issues for typical 1D PhC-based sensors is that the confined optical field does not fully overlap with analytes, which therefore leads to low sensitivity. Herein, we propose and numerically investigate a photonic crystal cavity by introducing a two tangent air hole array to improve the gas refractive index sensitivity. We also investigate the spectral feature of the proposed photonic crystal cavity for varying structure parameters and methane gas concentration. In addition, the coupling efficiency of the waveguide and the influence of the temperature on the proposed structure for sensing applications are analyzed. Theoretical analysis reveals that the proposed two tangent hole structure simultaneously achieves a high sensitivity (353 nm/RIU) and figure of merit (FOM = 1.2 × 104) compared to those observed in previous studies.

Ultrasensitive Electrochemical Methane Sensors Based on Solid Polymer Electrolyte-Infused Laser-Induced Graphene.

Methane is a potent greenhouse gas, with large emissions occurring across gas distribution networks and mining/extraction infrastructure. The development of inexpensive, low-power electrochemical sensors could provide a cost-effective means to carry out distributed sensing to identify leaks for rapid mitigation. In this work, we demonstrate a simple and cost-effective strategy to rapidly prototype ultrasensitive electrochemical gas sensors. A room-temperature methane sensor is evaluated which demonstrates the highest reported sensitivity (0.55 μA/ppm/cm2) with a rapid response time (40 s) enabling sub-ppm detection. Porous, laser-induced graphene (LIG) electrodes are patterned directly into commercial polymer films and imbibed with a palladium nanoparticle dispersion to distribute the electrocatalyst within the high surface area support. A pseudo-solid-state ionic liquid/polyvinylidene fluoride electrolyte was painted onto the flexible cell yielding a porous electrolyte, within the porous LIG electrode, simultaneously facilitating rapid gas transport and enabling the room temperature electro-oxidation pathway for methane. The performance of the amperometric sensor is evaluated as a function of methane concentration, relative humidity, and tested against interfering gases.

Ultrasensitive and robust organic gas sensors through dual hydrogen bonding

A dual hydrogen bonding-inspired polysquaramide sensor is able to detect ammonia as low as 10 ppt, the lowest among all ammonia sensors to date, and sense nitric oxide as low as 20 ppb. The sensor has outstanding robustness regarding selectivity, time-stability (>240 days), superior to other benchmarked organic electric sensors.

High‐Temperature Large‐Scale Self‐Assembly of Highly Faceted Monocrystalline Au Metasurfaces

AbstractLocalized surface plasmon resonance (LSPR) devices based on resonant metallic metasurfaces have shown disruptive potential for many applications including biosensing and photocatalysis. Despite significant progress, highly performing Au plasmonic nanotextures often suffer of suboptimal electric field enhancement, due to damping effects in multicrystalline domains. Fabricating well‐defined Au nanocrystals over large surfaces is very challenging, and usually requires time‐intensive multi‐step processes. Here, presented are first insights on the large‐scale self‐assembly of monocrystalline Au nano‐islands with tunable size and separation, and their application as efficient LSPR surfaces. Highly homogeneous centimeter‐sized Au metasurfaces are fabricated by one‐step deposition and in situ coalescence of hot nanoparticle aerosols into a discontinuous monolayer of highly faceted monocrystals. First insights on the mechanisms driving the high‐temperature synthesis of these highly faceted Au nanotextures are obtained by molecular dynamic and detailed experimental investigation of their growth kinetics. Notably, these metasurfaces demonstrat high‐quality and tunable LSPR, enabling the fabrication of highly performing optical gas molecule sensors detecting down to 3 × 10−6 variations in refractive index at room temperature. It is believed that these findings provide a rapid, low‐cost nanofabrication tool for the engineering of highly homogenous Au metasurfaces for large‐scale LSPR devices with application ranging from ultrasensitive optical gas sensors to photocatalytic macroreactors.