High-sensitivity Gas Research Articles

A New 3-D-Printed Nondestructive H-Like Resonant Fiber-Optic Photoacoustic Sensor for High-Sensitivity Remote Gas Sensing

A New 3-D-Printed Nondestructive H-Like Resonant Fiber-Optic Photoacoustic Sensor for High-Sensitivity Remote Gas Sensing

In-situ grown α-MoO3 hollow microspheres achieve high-sensitivity detection of trimethylamine

The direct in-situ growth synthesis method not only ensures a uniform thin layer and an optimized distribution of active sites but also significantly enhances gas adsorption and electron transfer efficiency. In this research, α-MoO3 hollow microspheres were successfully grown in-situ on a ceramic tube using a solvothermal method and applied to the highly sensitive detection of triethylamine (TEA). The α-MoO3 hollow microspheres, due to their unique nanostructure and optimized morphological characteristics, exhibited a high response of 90.965–50 ppm TEA at the optimal operating temperature of 217 °C, along with an ultra-low detection limit of 0.1 ppm. The sensitivity mechanism of α-MoO3 to TEA was deeply revealed through characterization techniques such as X-ray photoelectron spectroscopy (XPS), confirming its high selectivity in gas detection. Moreover, the sensor demonstrated excellent reliability in a long-term stability test over 180 days, providing a high-performance detection method for environmental monitoring and industrial safety fields. This research not only contributes a new perspective to the development of TEA detection technology but also provides important experimental evidence and theoretical support for the design and preparation of high-sensitivity gas sensors based on α-MoO3.

High-sensitivity multi-gas detection using dual-ridge metasurface emitters with polarization-distinguishable emission spectra

The metasurface thermal emitter offers an energy-efficient, compact, and sensitive solution as a radiation source for non-contact gas detection, enabling the “molecular fingerprint” technique to be widely applied, from medical diagnostics to environmental monitoring. However, most narrowband emitters are designed for a single target gas, hindering the miniaturization of multi-gas detection systems. In this work, a one-dimensional dual-ridge grating emitter is employed, achieving dual-band and tri-band polarization-distinguishable emission spectra through the excitation of Fabry-Perot (FP) resonances and quasi-bound states in the continuum (qBICs). These emission spectra can be readily matched to multiple non-overlapping absorption peaks of gases such as CH4, CO2, CO, NO, and NH3 within the 3–6 µm range, thereby reducing the impact of mixed gases on measurements. Compared to conventional metal-dielectric-metal structures, the use of a single metal layer results in lower material losses, enabling higher Q-factors and more pronounced directional radiation intensity variations. Furthermore, adjusting the asymmetry to modulate the qBIC-excited absorption peaks does not affect the Q-factor of the FP resonance absorption, thus achieving high-sensitivity multi-band gas detection. This work provides a promising approach for the miniaturization and integration of multi-gas channel detection, facilitating more accurate and sensitive sensing strategies.

Theoretically design of 2D penta-BN2/penta-Graphene wdW heterostructure for NO gas sensing implications: a first-principles study

As air pollution becomes more and more serious, the detection of harmful gas of NO has become an urgent need in daily life. In this paper, the electronic and gas-sensing properties of penta-BN2/penta-Graphene heterojunction (P-BN2/P-G) are studied by density functional theory and non-equilibrium Green's function method. The analysis results indicate that the P-BN2/P-G heterojunction has metallic properties. The electronic structures in combination with the adsorption behavior shows that the P-BN2/P-G heterojunction can chemically adsorb NO gas molecules, and there is obvious charge transfer, indicating that it has high gas sensitivity to NO gas. In addition, the sensing performance of the gas sensor constructed by NO adsorption on upper, middle and lower layers of the P-BN2/P-G heterojunction is deeply studied. Transport calculations show that when NO is adsorbed on the upper and middle layers of the P-BN2/P-G heterojunction-based gas sensor, the current of the device decreases significantly. When adsorbed on the lower layer, the current shows a trend of first decreasing and then increasing. Under a bias of 0.1 V, the gas sensitivity can reach up to 49% when NO is adsorbed in the middle layer, which is substantially higher than that of the P-BN2 monolayer device. It can be seen that the gas sensitivity is significantly improved after forming the heterojunction. In addition, the bias transport spectrum and scattering state can reveal the change in device current caused by the adsorption of NO gas molecules, thereby clarifying its microscopic mechanism. Finally, all the findings indicate that penta-based materials can be used as a very promising gas-sensitive material for detecting NO.

High sensitivity gas pressure and temperature optical sensors based on tapered no-core fiber coated with polydimethylsiloxane (PDMS)

This article introduces a novel high-sensitivity pressure and temperature sensor utilizing a tapered no-core fiber (NCF) structure created by splicing the NCF with a single-mode fiber (SMF) to form a “SMF-NCF-SMF” structure, tapering the NCF, and applying a polydimethylsiloxane (PDMS) film on the tapered NCF surface. The experimental results show that the device with a diameter of 10 μm has a pressure sensitivity of 86.63 nm/MPa within one to two atmospheres. Furthermore, the temperature sensitivity is −1.97 nm/°C from 30 °C to 60 °C. The sensor exhibits excellent stability and repeatability, and the PDMS film enhances the mechanical strength of the device, indicating promising potential for high-sensitivity pressure and temperature applications.

Flexible FPI sensor fabricated by fiber end photopolymerization and integration for high sensitivity gas pressure sensing

This work presents a new design framework for highly sensitive fiber gas pressure sensor. We construct a Flexible Fabry–Perot Interferometer (F-FPI), which consists of three polymer pillars and an end cap, on a fiber end face. A unique fiber-end photopolymerization and integration (FEPI) technique is adopted for fabricating the device. The varied gas pressure in the enclosed space not only changes the refractive index (RI) of the gas but also the length of the pillars. Therefore the difference in the optical path length of the FPI is more sensitive to pressure changes. Experimental results indicate that the F-FPI realizes a gas pressure sensitivity up to 79.0 pm/kPa in the range of 0–200 kPa. In addition, the Vernier effect is introduced to amplify the sensitivity to −409.7 pm/kPa. The temperature compensation is achieved by cascading a Fiber Bragg Grating (FBG) behind the F-FPI. Such a design framework provides a new idea for highly sensitivity gas pressure sensing.

Fabrication of MoS2-Fe3O4 heterostructure as an ultrafast and high-sensitivity NO2 gas sensor at room temperature

In this study, a novel MoS2-Fe3O4 heterostructure was fabricated for efficient detection of NO2 gas. The structural and morphological properties of MoS2-Fe3O4 composites were investigated by relevant characterization methods. The NO2 sensing performance of the sensor based on MoS2-Fe3O4 was tested. The result demonstrated that the MoS2-Fe3O4 sensor showed excellent performance with a high response of 25 and a fast response time of 6 s as exposed to 5 ppm NO2 at room temperature. In addition, this sensor also exhibited high sensitivity, satisfactory selectivity, excellent moisture resistance, favorable reproducibility and long-term stability. The enhanced gas sensing performance can be attributed to the synergetic effect of the abundant oxygen vacancy and p-n heterojunction.

Noncontact Fiber-Optic Cantilever-Enhanced Photoacoustic Spectroscopy.

Conventional cantilever-enhanced photoacoustic spectroscopy (CEPAS) usually requires the cantilever to be in contact with the gas, which limits its application in dusty and corrosive gas sensing. To overcome this challenge, this paper proposes noncontact fiber-optic cantilever-enhanced photoacoustic spectroscopy (NCFO-CEPAS) for high-sensitivity trace gas analysis. A polyethylene film with corrosion-resistant properties is affixed to the end of the cantilever acoustic sensor, and the effect of the distance between the polyethylene film and the cantilever acoustic sensor on the sensitivity of the system is analyzed by finite element analysis. Compared to the conventional CEPAS, NCFO-CEPAS has a lower background noise deviation. Besides, the potential damage to the silicon cantilever beam by corrosive gases can be avoided as the gas to be measured is not in contact with the silicon cantilever beam, and the gap of the cantilever beam will not be blocked in a high dust environment. Experimental results show that the detection limit of C2H2 gas is 0.5 ppm, and the normalized noise equivalent absorption coefficient reaches 5.93 × 10-9 cm-1 W Hz-1/2. The NCFO-CEPAS technique has the advantages of noncontact remote gas monitoring, not being corroded by gases, and high resistance to electromagnetic interference.

Simultaneous measurement of temperature and pressure sensing technology based on double cavity matching in batteries

A compact sensor based on fiber Fabry-Pérot (FP) cavities dual-cavity matching technique cascaded with fiber Bragg grating (FBG) is proposed and demonstrated to measure pressure and temperature variations inside battery. The sensitivity amplification mechanism for two-parameter measurements is analyzed and a cased reference chamber scheme is designed. Low-cost, small-size, high-temperature and corrosion-resistant all-fiber-optic high sensitivity gas pressure sensors targeting the interior of energy storage batteries are fabricated and cascaded with FBGs to measure temperature parameters. The experimental results show that the sensor has a sensitivity of −26.8322 nm/MPa in a pressure range of 1.86 MPa, the gas pressure inside the battery and the temperature inside and outside the battery at different discharge rates of 1500mAH capacity monobloc batteries can be measured practically, directly and instantly. It has potential applications in detecting subtle pressure variations caused by gas precipitation inside the battery and in temperature measurement, and provides a new concept and a feasible technological path for the measurement of key parameters inside lithium-ion batteries.

Perfect-absorption, High-sensitivity, and Low-thickness THz Gas Sensor Based on Tamm Plasmon Polaritons

Perfect-absorption, High-sensitivity, and Low-thickness THz Gas Sensor Based on Tamm Plasmon Polaritons

High sensitivity gas detection based on Au waveguide

Hydrogen, as a representative of the new energy source, has great potential for development, and the detection of the low concentration of hydrogen plays a crucial role in process safety control. In this paper, a gas sensor based on a metal-insulator-metal (MIM) structure with high sensitivity and low response time is proposed. The sensor is bilaterally coupled with a ring resonant cavity and a metal nanopillar, and the outgoing field superposition is achieved by bilaterally coupling the resonant cavity to achieve a lower transmittance, which facilitates detection. The symmetry of the structure was broken by different methods, and the results showed that the complexity and response time of the structure increased significantly after breaking the symmetry, but the transmittance appeared to decrease and the transmission characteristic curve was independent of the coupling phase. The waveguide structure shows a highly linear relationship between resonance wavelength and refractive index with a maximum sensitivity of 2433.00 nm/RIU when used for refractive index sensing, and a maximum sensitivity of −2.61 nm/% when used for hydrogen gas sensing. For methane gas sensing, the maximum sensitivity is −9.22 nm/%.

Short-length nanosecond pulsed 1.653-μm DBR fiber Raman laser oscillator fabricated by femtosecond laser direct-writing

We demonstrate a nanosecond pulsed 1.653-μm fiber Raman laser (FRL) oscillator in a short-length distributed Bragg reflector (DBR) cavity made by femtosecond laser direct-writing technique. The DBR FRL cavity is composed of commercial ultrahigh NA germanium-doped silica fiber with a short length of 10 m and a pair of fiber Bragg gratings (FBGs). The FBGs were directly inscribed on the ends of the Raman gain fiber, using femtosecond-laser point-by-point (PbP) writing method. A home-made 1.55-μm nanosecond fiber laser source was used as the pump of the FRL. 1.653-μm nanosecond pulsed laser oscillation with maximum average output power of 125 mW (corresponding to peak power of 6.6 W), 3 dB linewidth of ≤ 0.15 nm, and slope efficiency of 48 % was obtained under 1.55-μm pump with optimized repetition rate of 10 MHz. The optical signal-to-noise-ratio (OSNR) of the 1.653-μm narrow-linewidth Raman lasing is above 70 dB. The short-length DBR FRL output exhibits decently high degree of polarization (DOP) and high degree of linear polarization (DOLP) above 80 % in 3-hour period, benefitted from the birefringent FBGs made by femtosecond laser direct-writing method. It is expected that by further reducing the cavity length to < 1 m, the 1.653-μm DBR FRL oscillator made by femtosecond laser direct-writing method is promising as single-frequency narrow-linewidth, highly linearly polarized, high-OSNR laser sources for high-sensitivity CH4 gas detection.

High-sensitivity trace gas detection based on differential Helmholtz photoacoustic cell with dense spot pattern

A high-sensitivity photoacoustic spectroscopy (PAS) sensor based on differential Helmholtz photoacoustic cell (DHPAC) with dense spot pattern is reported in this paper for the first time. A multi-pass cell based on two concave mirrors was designed to achieve a dense spot pattern, which realized 212 times excitation of incident laser. A finite element analysis was utilized to simulate the sound field distribution and frequency response of the designed DHPAC. An erbium-doped fiber amplifier (EDFA) was employed to amplify the output optical power of the laser to achieve strong excitation. In order to assess the designed sensor's performance, an acetylene (C2H2) detection system was established using a near infrared diode laser with a central wavelength 1530.3 nm. According to experimental results, the differential characteristics of DHPAC was verified. Compared to the sensor without dense spot pattern, the photoacoustic signal with dense spot pattern had a 44.73 times improvement. The minimum detection limit (MDL) of the designed C2H2-PAS sensor can be improved to 5 ppb when the average time of the sensor system is 200 s.

Methane measurement method based on F-P angle-dependent correlation spectroscopy.

This study explores a gas measurement method based on Fabry-Perot (F-P) angle-dependent correlated spectroscopy, which achieves highly sensitive and selective gas measurements by adjusting the angle to match the F-P interference peak with the gas absorption peak. Methane (CH4) is the chosen target gas, and an F-P etalon is designed with parameters matching the CH4 absorption peak. An angle-scanning measurement system is established to enable correlated spectroscopic detection of CH4 gas. Angle-scanning measurements reveal distinct absorption signals at the angle where the F-P interference peak aligns with the CH4 absorption peak. Gas measurements of standard samples demonstrate a linear relationship between the apparent absorbance at the on/off positions and CH4 concentration, allowing for accurate CH4 concentration measurements. The study further investigates the detection limit of the experimental system, achieving a 3σ detection limit of 720 ppm under the on/off measurement mode. A conical incidence model is developed to analyze the impact of beam divergence angles on the transmittance of the F-P cavity. Simulations are conducted to assess absorption signals in the presence of extreme cross-interference, demonstrating the method's robust resistance to cross-interference. The F-P correlated spectroscopy method described in this paper, as a non-dispersive spectroscopic measurement technique, holds promise for designing high-sensitivity gas sensors and imaging applications.

A concave octahedral hollow SnO2 nanocage for enhancing typical electrolyte (EMC) leakage gas sensing performance in lithium-ion batteries

The safety issues caused by lithium-ion battery (LIB) failures are the pain points that constrain the development of LIB. Developing a high sensitivity and low-cost gas sensor targeting trace electrolyte vapors, such as methyl ethyl carbonate (EMC), can help achieve early warning in accidents. Tin dioxide (SnO2) has always been one of the most widely used gas sensitive materials. Herein, the concave octahedral hollow SnO2 nanocages (SnO2-Hoc) are quickly prepared by template-engaged coordinating etching. The response value of its sensor to 10 ppm EMC is 7.24 at 140℃ and it shows sufficient sensitivity in LIB leakage simulation tests. The hollow concave octahedral structure promotes the EMC diffusion, and the lower energy barrier of EMC cleavage is the key to selective response. Overall, this work synthesized SnO2-Hoc sensor to directly detect trace EMC, which is expected to provide new guarantees for the LIB safe application.

High-sensitivity ammonia gas sensor based on hollow microsphere MXene@SnS2@polyaniline composite material with humidity resistance

Conductive polymer-based gas sensors are frequently utilized because of their benefits, which include affordability, good gas selectivity, and room-temperature detection. However, they are still limited by low sensitivity, high detection limit, and slow response-recovery speed. In this study, a hollow flower-shaped composite gas-sensing material was designed. MXene microspheres formed by electrostatic adsorption using Polymethyl Methacrylate (PMMA) as a template were used as substrates, and SnS2 nanosheets were produced hydrothermally on the MXene microsphere surface to form flower-shaped gas-sensitive materials. After calcination to remove the template, polyaniline (PANI) was coated onto each SnS2 nanosheet via in situ polymerization. The synthesized MXene@SnS2@PANI nanoflowering composites exhibited an extremely high responsiveness to ammonia gas at 25 °C, extremely low detection limits, and unique selectivity towards ammonia gas. When exposed to 100 ppm NH3 at 25 °C and 45% relative humidity (RH), the MSP-100 gas sensor's reaction reached 119.76%, which was five times that of PANI. Notably, in the range of 0%–90% RH, the MSP-100 based gas sensor's reaction grew as humidity rose, reaching a peak response of 215.18% at 90% RH. In addition, the MXene@SnS2@PANI based gas sensor had an extremely low detection limit of 1.557 ppm and prominent selectivity, indicating the its promising application in ammonia gas detection.

A synergistic combination of 2D MXene and MoO3 nanoparticles for improved gas sensing at room temperature

MXene Ti3C2T x (30% HF-etched, named Ti3C2T x -30) plays a pivotal role in the substantial enhancement of the structural modification of molybdenum trioxide (MoO3). Additionally, as the surface MoO3 molecules come into contact with reducing gas moieties, they actively participate in gas sensing at room temperature. The percentage of Ti3C2T x -30 in the MoO3 matrix was varied at 10%, 20%, and 40%, denoted as MM-10, MM-20, and MM-40, respectively. Structural analysis confirmed the composition of the basic elements and evolution of TiO2 at a higher percentage of Ti3C2T x -30. Spectroscopy analysis showed the interactions between Ti3C2T x -30 and MoO3, showcasing work functions of 6.91 eV, 6.75 eV, and 7.21 eV for MM-10, MM-20, and MM-40, respectively, confirming MM-20 to be an optimum composition. When the samples were exposed to ammonia gas, MM-20 showed a high response (93% for 100 ppm) at room temperature, with a response time of ∼10 s. Compared to bare MoO3, these samples showed ten-fold improvement. The excess electrons on the surface of Ti3C2T x -30 facilitate the formation of O2− species, which also provides stability to the otherwise highly reactive MXene surface. These species actively react with ammonia molecules in the presence of adsorbed MoO3, thereby changing the resistance of the system. This can be a significant step towards imparting high gas sensitivity to metal oxides at room temperature via incorporation of an optimum percentage of optimized Ti3C2T x .

A DFT study of natural-based materials kaempferol and apigenin for hazardous CO and CO2 gas detection

In this research, the chemical and structural attributes of two flavonoid compounds, Kaempferol and Apigenin, have been investigated employing DFT. These compounds are considered the most promising options for high-sensitivity gas sensors. Applying DFT computations, the adsorption behaviour of typical gas molecules over Kaempferol and Apigenin was studied. Apigenin (Kaempferol) could respond to physisorption of CO and CO2 molecules sensitively due to their considerable charge transfer (CT). Particularly, notable progress in transport performance is induced by absorption of both CO and CO2, which makes Apigenin (Kaempferol) an appropriate option to detect CO and CO2 molecules sensitively. In order to examine potential application of natural products in sensing toxic gases, we deeply believe that this work supplies guidance for research groups.

A novel Cu-doped ZnO confined structure: Precisely preparation, and sensitization mechanism for ppb-level H2S gas detection

It is still highly desired and challengeable to design H2S sensor with high selectivity and sensitivity due to its toxicity and new application in biomarkers like monitoring halitosis. Here, we reported a novel confined structure as highly sensitive and selective H2S gas sensor. The sensing material was prepared with a HKUST-1 templated method by atomic layer deposition (ALD) ZnO decorated on HKUST-1 and calcination. The gas sensor exhibits a high gas sensitivity (Ra/Rg = 2.67 @ 2 ppm) with excellent selectivity to H2S. Furthermore, the obtained sensor shows ppb-level detection ability (Ra/Rg = 1.13 @ 0.1 ppm). Apart from releasing electrons by the oxidization of H2S on oxygen vacancies with adsorbed oxygen species O2− on ZnO surface (Langmuir-Hinshelwood mechanism), the Cu was proved to be the active sites, and would react with surficial S species. The suggestion was confirmed by operando XAS (X-ray adsorption spectrum) measurements combined with DFT calculations (Mars-van Krevelen mechanism). This work provides valuable insights for developing efficient sensing materials and understanding the sensing mechanism.

A solar-powered self-clean gas-sensing neural modulator for behavioral intervention with spatiotemporal flexibility

The amalgamation of high-sensitivity gas sensors with neural electrical stimulation technology stands as a compelling solution for eliciting behavioral responses in the presence of low-level hazardous gases. The utilization of battery-powered or coil-based configurations introduces spatiotemporal limitations, encompassing constrained experimental durations due to battery life or the necessity to confine subjects to specific locales for wireless power transmission. In this study, we present an advanced wireless neural modulator, meticulously engineered for behavioral intervention in unrestricted environments. This device integrates a solar-powered unit, gas sensor, brain stimulation signal management system, and a neurostimulation electrode. The solar energy utilization eliminates the necessity for battery replacements and local range limitations. The surface of the solar cells is treated with a superhydrophobic coating, enhancing performance in outdoor settings by mitigating surface contamination issues inherent in traditional solar cells. This innovation guarantees continuous, long-term, on-demand operational capacity, ensuring uninterrupted power supply to the system. Experimentation revealed shortened locomotor activity in mice, induced by stimulation of the periaqueductal gray (PAG) brain region, for up to thirty minutes. These results underscore the significant potential of our technology for spatially and temporally unrestricted neuromodulatory applications, offering a viable strategy to alleviate the detrimental effects of hazardous gas exposure on physiological functions.