Search

Nanostructures possessing plasmonic and magnetic properties can enhance the transverse magneto-optical Kerr effect (TMOKE) by exciting surface plasmon resonances (SPRs). This provides a promising platform for magneto-optical SPR sensors with significantly improved sensing performance. Here, we propose a high-performance magneto-optical SPR sensor, which consists of a bilayer Au/Co grating placed on a gold film. By tuning the structural parameters, a Fano-like TMOKE spectrum with a linewidth of only 0.0135 nm and an amplitude approaching the theoretical maximum is obtained. We attribute the optimal TMOKE signal achieved by the sensor to the critical coupling concept which is associated with the trade-off between scattering and intrinsic decay rates of the system. The optimized nanostructure sensor demonstrates a sensitivity of 1432 nm/RIU to refractive index fluctuations as small as 0.0001 in air, and all figures of merit (FOM) up to 105 RIU−1, making it suitable for gas sensor fabrication. [ABSTRACT FROM AUTHOR]

Low power, high sensitivity, and selectivity chemiresistive gas sensors are in urgent demand for hydrogen sulfide (H2S) detection to protect human health and the world's ecosystem. In this study, multiwalled carbon nanotubes (MWCNTs) and copper oxide (CuO) submicrometer size particles' compositions were utilized to fabricate low-temperature H2S gas sensors, which were prepared using a screen-printing technique on inter-digited patterned SiO2/Si substrates. The heterostructure of MWCNT@CuO was confirmed through high-resolution transmission electron microscopy analysis and x-ray diffraction patterns. The x-ray photoelectron spectroscopy analysis reveals the chemical states, binding energies, and oxygen vacancy (Ov). Brunauer–Emmett–Teller analysis of nitrogen physisorption analysis was conducted on the samples to analyze sensor surface areas and pore size distribution. The as-fabricated MWCNT@CuO sensor shows a relative response (ΔR/R%) of 73% toward 10 ppm H2S at 50 °C temperature in a selective manner, which is 1.6 times higher than that of devices based on bare CuO. The MWCNT@CuO interface modifies the morphology and also constructs a p–p heterojunction. This leads to the reforming of the band structure and results in a low resistance of the matrix, as well as a high chemisorbed oxygen content. The use of metal oxide semiconductors with MWCNTs offers a promising approach for the development of high-performance gas sensors that are energy-efficient. [ABSTRACT FROM AUTHOR]

A hydrogen sensor is created on the basis of an acoustic topological material with a coiled structure. Compared to traditional hydrogen sensors, the sensor does not possess a sensitive layer and works with the shift of a topological interface state induced by hydrogen. The sensor is composed of two phononic crystals with distinct topological characteristics, and an interface state is achieved at the interface of both phononic crystals. When hydrogen is introduced into the sensor, the density and the sound velocity of the gas in the sensor change, which shifts the frequency of the interface state. Thus, the concentration of hydrogen can be obtained by measuring the frequency shift of the interface state. Due to the absence of a sensitive layer, the sensor operates without a chemical sorption process, and the performance of the sensor is marginally influenced by working conditions, temperature, and humidity. Theoretical analysis, numerical simulations, and experimental results show that in different background gases, synthetic air, nitrogen, and argon, the sensor exhibits relative sensitivities of 0.50, 0.50, and 0.37, which do not change with the working conditions. Additionally, the sensor possesses a rapid response, a good linearity and robustness, and a long lifespan. Furthermore, the sensor is designed based on a coiled structure, which considerably improves the space utilization and decreases the bulk. [ABSTRACT FROM AUTHOR]

It is a novel-effective process for realizing high-efficiency sensing and continuous gas monitoring by introducing precious metals into metal–oxide–semiconductors (MOSs). In this study, Ag is exploited to prepare surface functionalized SnO2 nanoparticles (NPs) and innovative xAg@SnO2/CsPbBr3, activating and catalyzing the gas sensing reactions on semiconductors. The results show that the precious metal Ag NPs promote the directional transport of carriers, thus improving the gas sensing performances. In addition, innovative xAg@SnO2/CsPbBr3 composites originated from Ag@SnO2 NPs and 3-mercaptopropionic acid treated all-inorganic perovskite CsPbBr3 are constructed to further accelerate electron transfer on heterointerfaces, enabling continuous and efficient monitoring of ethanolamine (EA) at room temperature. The sensing properties of Ag@SnO2/CsPbBr3 on various volatile organic compounds are investigated. Compared with pure CsPbBr3, the EA response of as-prepared 2Ag@SnO2/CsPbBr3 is obviously improved by about sevenfold. The response/recovery time is greatly shortened, besides the good stability. Another interesting result for xAg@SnO2/CsPbBr3 is the lower limit of detection of 44.43 ppb. The work demonstrates that Ag modification facilitates the adsorption/desorption rate and the response. Furthermore, the catalytic activation of noble metal Ag NPs and the synergistic interaction of SnO2/CsPbBr3 nano-heterojunctions promote EA sensing performances at room temperature. [ABSTRACT FROM AUTHOR]

InN holds great promise for a wide range of applications, including broadband optical devices, high-frequency electronic devices, and serving as a substrate for highly sensitive gas detectors and efficient catalysts. Nevertheless, production of high-quality InN thin films through epitaxy has remained a significant challenge. This is primarily due to complexities arising from the low dissociation temperature and the high N2 equilibrium pressure of InN, which lead to formation of numerous nitrogen vacancies and a propensity to generate indium metal nanoparticles. Efficacy of the indium bilayer pre-deposition method for InN film growth has been established in prior studies. In this work, we introduce a specialized hydrogen insertion method to further enhance nitridation of the indium bilayer. The corresponding kinetic mechanism has been demonstrated through theoretical simulations and practical epitaxy experiments, leading to the development of an optimized hydrogen insertion process. This research represents a substantial improvement over existing InN epitaxial methods that involve control of the indium bilayer and introduces a novel mechanism for enhancing InN heteroepitaxy. [ABSTRACT FROM AUTHOR]

SnO2 is a prototypical transparent conducting oxide that finds widespread applications as transparent electrodes, gas sensors, and transparent thin-film devices. Hydrogen impurities in SnO2 give rise to unintentional n-type behavior and unexpected changes to conductivity. Interstitial H (Hi) and H at an oxygen vacancy (HO) are both shallow donors in SnO2. An O–H vibrational line at 3155 cm−1, that can be produced by a thermal anneal at 500 °C followed by a rapid quench, has been assigned to the Hi center and is unstable at room temperature on a timescale of weeks. An IR absorption study of the decay kinetics of the 3155 cm−1 O–H line has been performed. The disappearance of Hi upon annealing has been found to follow second-order kinetics. Measurements of the decay rate for a range of temperatures have determined an activation energy for the diffusion of interstitial H in SnO2. These results provide fundamental information about how unintentional hydrogen impurities and their reactions can change the conductivity of SnO2 device materials in processes as simple as thermal annealing in an inert ambient. [ABSTRACT FROM AUTHOR]

SnO2 is a prototypical transparent conducting oxide that finds widespread applications as transparent electrodes, gas sensors, and transparent thin-film devices. Hydrogen impurities in SnO2 give rise to unintentional n-type behavior and unexpected changes to conductivity. Interstitial H (Hi) and H at an oxygen vacancy (HO) are both shallow donors in SnO2. An O–H vibrational line at 3155 cm−1, that can be produced by a thermal anneal at 500 °C followed by a rapid quench, has been assigned to the Hi center and is unstable at room temperature on a timescale of weeks. An IR absorption study of the decay kinetics of the 3155 cm−1 O–H line has been performed. The disappearance of Hi upon annealing has been found to follow second-order kinetics. Measurements of the decay rate for a range of temperatures have determined an activation energy for the diffusion of interstitial H in SnO2. These results provide fundamental information about how unintentional hydrogen impurities and their reactions can change the conductivity of SnO2 device materials in processes as simple as thermal annealing in an inert ambient. [ABSTRACT FROM AUTHOR]

Cupric oxide (CuO) is a promising p-type semiconducting oxide used in many critical fields, such as energy conversion and storage, and gas sensors, which is attributed to its unique optoelectrical properties and cost-effectiveness. This work successfully deposited amorphous, pinhole-free, ultrathin CuO films using atmospheric pressure spatial atomic layer deposition (SALD) with copper(II) acetylacetonate and ozone as precursors. The growth rate increased from 0.05 Å/cycle at 175 °C to 0.35 Å per cycle at 275 °C. XPS and XRD confirmed the formation of a pure CuO phase, with typical strong satellite shake-up peaks, and a tenorite crystalline phase. The films exhibited semiconducting behavior, with temperature-dependent electrical measurements revealing the Fermi level positioned 0.2–0.24 eV above the valence band. Furthermore, p-type CuO was combined with n-type ZnO, both deposited by SALD, to form a high-performance photodiode. This CuO/ZnO heterojunction demonstrated excellent rectifying behavior, with an ION/IOFF ratio of 2.04 × 103, and functioned as an efficient UV detector, showing fast response and good repeatability. These results highlight the potential of SALD-deposited CuO thin films for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) detection with novel sensing properties such as higher response and minimum detection limit at room temperature is essential to ensure the safety of humans and the environment. A hydrothermal method was utilized to synthesize NiO–ZnCo2O4 heterostructures. The purpose of these materials was to fabricate gas sensors and detect different hazardous gases. The intrinsic properties of synthesized products were studied to check the microstructure and morphological properties of the heterostructures. Different gas sensors performed gas sensing properties, and the significant properties such as high response (ratio of response in gas and response in air R g ∕ R a = 2 9 0) towards 20 ppm H2S, short response/recovery time (32/20 s), a low detection limit (0.5 ppm), and great selectivity were detected based on the gas sensor of NZCO-5 (5% NiO–ZnCo2O4) compared with other sensors NiO, NZCO-0 (0% NiO–ZnCo2O4) and NZCO-10 (10% NiO–ZnCo2O4). The significant H2S gas sensing improvement in this study could be a potential route for saving human lives. [ABSTRACT FROM AUTHOR]

In this work, we have investigated and compared three important parameters: resistance, absorbance, and sensitivity of the sensitive layer in the ammonia gas sensor made of conductive polymers. Using a simulation based on the Langmuir absorption model, we have examined the changes in resistance, absorbance, and sensitivity of both the pure conducting polymer and the layer doped with carbon nanotubes. We analyzed the results using Matlab software. The findings demonstrate that the addition of carbon nanotubes reduces the resistance and enhances the absorbance and sensitivity. [ABSTRACT FROM AUTHOR]

The detection of toxic and flammable gases represents a critical challenge in the field of health physics, given its implications for safety and environmental monitoring. This study introduces a novel co-precipitation method for synthesizing pure and iron (Fe)-doped SnO₂ nanoparticles (NPs) specifically designed for the detection of various hazardous gases. Utilizing advanced characterization techniques such as X-ray diffraction, FTIR, EDX, and XPS, we validate the structural integrity, elemental composition, and chemical states of the synthesized samples. Notably, an observable red shift in the UV–Vis absorption spectra correlates with the introduction of Fe, which results in smaller grain sizes. Photoluminescence analysis further confirms the presence of defects, including oxygen vacancies, that enhance the sensing capabilities of these materials. Morphological examinations via scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HR-TEM) reveal a distinct spherical morphology of the synthesized samples, indicating their potential for gas sensing applications. Importantly, our findings demonstrate that the sensing performance of Fe-doped SnO₂ NPs significantly surpasses that of pure SnO₂, showcasing excellent detection capabilities with a remarkable response of 92.028 towards 100 ppm of H₂S gas. Furthermore, sensor-3 (3 % Fe-doped SnO₂) exhibits commendable selectivity when compared to various gases such as NH₃, C₃H₆, and CO. These attributes suggest that our synthesized Fe-doped SnO₂ NPs could serve as highly effective H₂S gas sensors, with promising applications in industrial safety and environmental monitoring. [ABSTRACT FROM AUTHOR]

Bi 2 O 3 microspheres modified with CeO 2 were successfully synthesized via the hydrothermal method, and a gas sensor based on this composite material was prepared. Various analytical techniques were employed to examine the morphological and structural characteristics of the Bi 2 O 3 /CeO 2 composites. The synthesized Bi 2 O 3 microspheres exhibited a uniform size, with a particle diameter of approximately 2.5 μm. CeO 2 nanoparticles could be clearly observed on the surface of the Bi 2 O 3 microspheres. The results of X-ray photoelectron spectroscopy revealed that the adsorbed oxygen and oxygen vacancies on Bi 2 O 3 doped with CeO 2 increased, potentially due to the presence of Ce3+/Ce4+ ions. The Bi 2 O 3 /CeO 2 sensors demonstrated significantly enhanced sensing properties for formaldehyde at room temperature. At a formaldehyde concentration of 100 ppm, the reactivity of the Bi 2 O 3 /CeO 2 sensor was 137 %, exhibiting a 6.6-fold enhancement compared to the Bi 2 O 3 sensor. Furthermore, the adsorption energy, differential charge density, and state density of the sample were calculated using density functional theory (DFT). Subsequently, the gas-sensing mechanism was analyzed and discussed. The results indicate that CeO 2 -modified Bi 2 O 3 nanospheres can enhance the adsorption energy of formaldehyde. The formation of a heterojunction facilitates electron transfer, thereby improving the gas-sensing properties. Furthermore, the gas sensing mechanism was discussed and analyzed using density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Baseline drift is a common problem associated with metal oxide semiconductor based gas sensors operating at room temperature. There have been theoretical approaches to eliminate the errors involved in the response and sensitivity calculations due to baseline drift of gas sensors. However, no such experimental strategy such as using novel oxide semiconductors and their composites with stable electrical resistance, has so far been developed. We have observed that room temperature volatile organic compound gas sensing properties of tungsten tri-oxide (WO 3) nanocrystals can be significantly enhanced by compositing them with graphitic carbon nitride (g-C 3 N 4). Improved performances characterized by increased responses and reduced baseline drifts have been observed for WO 3 /g-C 3 N 4 nanocomposite based gas sensors. Tungsten tri-oxide (WO 3) nanocrystals were synthesized by hydrothermal method. Similarly, graphitic carbon nitride (g-C 3 N 4) was synthesized by thermal poly-condensation of melamine. WO 3 /g-C 3 N 4 nanocomposite was obtained by grinding above powders in an agate mortar and pestle followed by sintering at 450 °C for 2 h. Volatile organic compound gas sensing properties of WO 3 /g-C 3 N 4 nanocomposite based sensors were studied at room temperature. WO 3 /g-C 3 N 4 nanocomposite showed better stability and higher response compared to pristine WO 3. Very small baseline drift was observed with WO 3 /g-C 3 N 4 nanocomposite based sensors during volatile organic compound (VOC) gas sensing. Response of WO 3 /g-C 3 N 4 nanocomposite towards 636 ppm ethanol gas, for example, was more than 20 % higher than that of WO 3. The response and baseline resistance drift were measured for WO 3 /g-C 3 N 4 pellets having varying weight percentages of WO 3 and g-C 3 N 4. With an increase in g-C 3 N 4 content, baseline drift and response decline due to an increase in sensor material resistance. Selectivity of the sensor was examined by using three target gases: acetone, ethanol and formaldehyde. 50%WO 3 /50%g-C 3 N 4 (w/w) nanocomposite showed 91 % response to 1272 ppm ethanol gas whereas the limit of detection for ethanol gas was 106 ppm. Innovation points of this work includes enhanced sensitivity, very small baseline drift and stable room temperature operation of WO 3 /g-C 3 N 4 nanocomposite based ethanol gas sensors. Enhanced ethanol sensing properties of WO 3 /g-C 3 N 4 nanocomposite at room temperature invite its possible application in commercial volatile organic compound gas sensors in future. [ABSTRACT FROM AUTHOR]

Ethylene glycol (EG) is a toxic organic compound, which is harmful to human body. Hence, the advancement of gas-sensitive materials for the efficient detection of ethylene glycol (EG) holds significant practical value. This study successfully synthesized Bi 2 MoO 6 (BMO), In 2 O 3 , and BMO/In 2 O 3 composite samples through the hydrothermal method. Among them, BMO/In 2 O 3 composite has a spherical structure with a rough surface, has good gas sensitivity to EG, can achieve a higher response to 100 ppm EG (S = 38), and has a lower optimal operating temperature (220 °C) compared with BMO pure sample. The innovation lies in the construction of BMO/In₂O₃ heterojunction, which changes the microstructure and electron transport properties of the material, thus significantly improving the gas sensing performance. BMO/In 2 O 3 sensors have good selectivity, excellent moisture resistance and long-term stability. The combination of In 2 O 3 with other materials changes the microstructure of the sample, including the material particle size, optical band gap width, and vacancy oxygen ratio, and finally improves the utilization rate of the sensitive body, thus enhancing the gas-sensitive performance. The bilayer sensor has shown great application value. It can achieve super-selectivity and high-sensitivity detection of low-concentration EG at a low cost, which makes it easier to detect low-concentration EG. These results show that a BMO/In 2 O 3 composite was prepared by a hydrothermal method and applied to glycol gas sensing. The composites have higher response values and lower operating temperatures compared to pure BMO. The crystal structure, micromorphology, optical and electronic properties were investigated, and the gas sensing performance and mechanism were discussed. In addition, real-time monitoring of glycol concentration was realized, demonstrating the potential of this sensor for practical applications. [ABSTRACT FROM AUTHOR]

In this study, the conductive polyaniline doped by hydrochloric acid (PANIHCl)/zinc oxide (PANIHCl/ZnO) conductive composite was synthesized by in-situ polymerization. The conductive PANIHCl solution or PANIHCl/ZnO conductive composite solution was coated on an interdigital electrode (IDE) by drop coating to make a humidity sensor. The synthesis process, chemical structure, surface morphology, and humidity sensing characteristics of PANIHCl and PANIHCl/ZnO conductive composite were investigated. Field emission scanning electron microscope (FE-SEM) images suggested that the surface morphology of the PANIHCl/ZnO conductive composite is fibrous or rod-shaped, with a diameter of about 100 nm. The sensing responses of PANIHCl and PANIHCl/ZnO were 40% and 87%, respectively. The humidity sensing response of PANIHCl/ZnO as the sensing material was more than twice that of PANIHCl as the sensing material. The response time (Tres) is 13 s, and the recovery time (Trec) is 171 s. Research results showed that adding ZnO to PANIHCl can effectively improve the response of the sensor to humidity detection. Therefore, using PANIHCl/ZnO conductive composite as a sensing material will have great potential for application in humidity or other gas sensing devices. [ABSTRACT FROM AUTHOR]

The power-boosted laser transmitted via a fiber tip sinusoidally excites the target trace molecules, generating a photothermal (PT) effect. The Gaussian-distributed plane wave heats the medium adjacent to the Fresnel reflection surface. Meanwhile, a continuous probe light traverses the heating field, and the periodic temperature change then modulates the phase of the probe light. A multi-beam interferometer formed by aligning the Fresnel reflection surface to a gold-coated high-reflection surface possesses high resolution and sensitivity, significantly enhancing the detection performance. A well-established theoretical model of instantaneous PT transduction and optical phase modulation is employed to obtain the optimized interferometric configuration. To validate the effective interferometric phase transformation within the cavity, a comparison is made between the simple silicon cavity and the gold-coated cavity. The limitation of detection of such extrinsic fiber-tip PT sensors indicates one magnitude lower as compared to the conventional PT interferometric gas sensor with such robust and compact sensing designs. This work lays a solid foundation for future research on gas laser phase modulators and nonlinear laser–matter interactions. [ABSTRACT FROM AUTHOR]

In order to achieve high sensitivity in gas-sensors based on organic field-effect transistors (OFETs), the most crucial and direct approach to enhance their sensing performance and reduce response and recovery times was through appropriate modification or improvement of the organic semiconductor (OSC) layer, such as altering its surface morphology or structure. The micro/nanostructure of spin-coated copper phthalocyanine (CuPc) films was controlled by utilizing polyvinyl alcohol ordered nanofibers (PVA ONFs). The electrical and gas-sensitive properties of CuPc/PVA ONF films were investigated and analyzed. CuPc/PVA ONF film transistors exhibited improved output and transfer characteristics when the CuPc solution concentration was 75 mg mL−1, with a mobility (μ) of 6.90 × 10−4 cm2 V−1 s−1. Compared with the spin-coated CuPc film transistors, the mobility increased by 74.24%. The sensors demonstrated a relative response of 12 942% to 20 ppm NO2 gas. Additionally, they showed a response time of 1.49 min and a recovery time of 2.32 min. The response rate reached up to 90%, while the sensitivity was measured at 611%/ppm, and the limit of detection (LOD) stood at 0.2 ppm. The research presented in this article advances the potential applications of phthalocyanine materials within the realm of flexible and 3D-printed sensing technologies. [ABSTRACT FROM AUTHOR]

This paper presents a MEMS-based hydrogen sensor that utilizes a cantilever functionalized with palladium. Using rotary electrostatic actuators, the cantilever resonates in in-plane mode which is not complex and compatible with CMOS technology. This sensor works with the lowest viscous damping, and in addition, it is label-free. In the present investigation, solid mechanics module is used for the structural simulation of the sensor. The resulting parameters including oscillation frequency, quality factor, and sensitivity are obtained by the finite element method using 3D simulations. The results show that the quality factor is as high as 1017 at resonance frequency of 305. 25 kHz. Moreover, the resonator sensitivity is about 1 Hz/ppm. • Resonant frequency shift method is studied in order to detect hydrogen gas. • Couette and Stokes models are used to obtain quality factor of the resonator. • The frequency of 305.25 kHz is investigated for in-plane rotational motion. • The quality factor and sensitivity are achieved 1017 and 1 Hz/ppm, respectively. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2), as a clean energy source, exhibits significant promise in the realm of new energy vehicles. Utilizing hydrogen sensors with rapid response and high selectivity is crucial for monitoring vehicles and preventing hydrogen leakage incidents. In this study, In 2 O 3 nanomaterials were synthesized via a hydrothermal approach and effectively modified with Ag/Cu bimetallic nanoparticles to fabricate high-performance hydrogen sensors. The optimal work temperature for the Ag/Cu–In 2 O 3 sensor is determined to be 300 °C. At this temperature, the sensor exhibited a response of 9.66–100 ppm H 2 , which is four times higher than the pristine In 2 O 3 sensor. Excellent H 2 selectivity and outstanding long-term stability were exhibited by the sensor in typical interference gas environments encountered in new energy vehicles. The significant enhancement in sensor performance is attributed to the electronic and chemical sensitization effects of Ag/Cu bimetals and the synergistic effects of bimetallic modification. Additionally, computational studies based on density functional theory (DFT) further elucidated the reasons for the improved H 2 gas sensing performance of Ag/Cu–In 2 O 3 nanocomposites. The Ag/Cu–In 2 O 3 nanocomposites show great potential for hydrogen detection applications in the sensor field. • Ag/Cu bimetallic-modified In 2 O 3 nano-sensing materials were synthesized. • Ag/Cu–In 2 O 3 sensor showed excellent H 2 selectivity and rapid response time at 300 °C. • The gas sensing mechanism of Ag/Cu–In 2 O 3 were analyzed using DFT calculations. [ABSTRACT FROM AUTHOR]

This study describes an easy and cheap inkjet printing method for producing a paper-based gas sensor consisting of a composite film made of graphene oxide and poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate) (PEDOT:PSS). A glossy paper substrate is an inkjet printed with ink made by dispersing graphene oxide in a PEDOT:PSS conducting polymer solution to test its ability to detect ammonia ( NH 3) at ambient temperature. The presence of few-layer graphene oxide in the PEDOT:PSS copolymer and the existence of π – π interactions between graphene oxide and PEDOT:PSS are confirmed by Fourier transform infrared spectroscopy, UV–Visible spectrophotometer, and X-ray diffraction. In a small concentration range of 1–100 ppm at ambient temperature, the ink-jet printed graphene oxide-PEDOT:PSS gas sensor displays strong responsiveness and good selectivity to NH3. The study found that NH 4 is a strong donor in the ammonia gas produced by a bubble system of ammonia water, with NH 4 molecules being ideal candidates for molecular doping of graphene. The H 2 O molecule can facilitate quick desorption by converting NH 3 to NH 4 . The interaction between graphene oxide and NH 3 molecules is weak. The attained gas-sensing performance may be attributed to the increased specific surface area of graphene oxide and enhanced interactions between the sensing film and NH 3 molecules via π and lone pair electron network. The NH 3 -sensing mechanisms of the flexible printed gas sensor are based on the competitive interaction of ammonia on the sensor, adsorption and dissociate ionization on the sensor surface. [ABSTRACT FROM AUTHOR]

Efficiently managing agricultural waste while innovating to derive value-added products is a significant challenge in the 21st century. In recent decades, these by-products have been increasingly explored as alternative sources for materials such as biosilica. Biosilica is renowned for its high surface area, biocompatibility, chemical stability, and modifiable surface, which makes it suitable for various applications. Additionally, the biomineralization process—biosilicification—in living organisms like diatoms offers an eco-friendly pathway for silica production. Despite the potential applications of biosilica, research on its use in sensor technology remains limited. This review aims to address this gap by covering the primary methodologies for extracting silica from biomass, discussing key techniques for its characterization, and highlighting its potential for functionalization in diverse applications. Special emphasis is given to the utility of diatom-derived biosilicas in developing sensors for detecting gaseous molecules and biomolecules. [Display omitted] • Green sources for biosilica include rice husks, wheat straw, sugarcane bagasse, and diatoms. • Key biosilica functionalization with metals, enzymes, nanoparticles, and ligands is described. • Advances in diatom-derived biosilica for detecting biomolecules and gases are highlighted. [ABSTRACT FROM AUTHOR]

Currently, semiconductor gas sensors are being actively studied and used in various fields, including ecology, industry, and medical diagnostics. One of the major challenges is to reduce their operating temperature to room temperature. To address this issue, sensor layers based on WO3−x/WS2 nanostructures synthesized by the hydrothermal method have been proposed. In this paper, the morphology of the material's surface and its elemental composition were investigated, as well as the optical band gap. Additionally, changes in the resistance of the WO3−x/WS2 sensor layers under the influence of alcohol vapors at room temperature were analyzed. The results showed that the layers exhibited a significant response, with short response and recovery times. The achieved response value to 1000 ppm of isopropanol was 1.25, with a response time of 13 s and a recovery time of 12 s. The response to 1000 ppm of ethanol was 1.35, and the response and recovery times were 20 s. This indicates that these sensor layers have promising potential for various applications. [ABSTRACT FROM AUTHOR]

The essential oil extracted from the flowers of Chrysanthemum zawadskii var. latilobum (Maxim.) Kitam (CZEO), family Asteraceae, was investigated to determine its ability to inhibit the pathogenicity of methicillin-resistant Staphylococcus aureus (MRSA). The chemical composition of CZEO was analyzed using gas chromatography–flame ionization detector and gas chromatography–mass spectrometry, and 88 compounds were identified and categorized as monoterpenes (68.82%), sesquiterpenes (17.82%), and others (5.01%). CZEO inhibited MRSA floating cell growth, acid production, and biofilm formation in a concentration-dependent manner. Furthermore, confocal laser scanning and scanning electron microscopy confirmed that the CZEO treatment decreased MRSA viability and notably reduced the three-dimensional density of the biofilm. Real-time PCR demonstrated that the mRNA expression of the MRSA gene A (mecA), accessory gene regulator A (agrA), staphylococcal accessory regulator A (sarA), and staphylococcal enterotoxin A (sea), which are pivotal genes implicated in MRSA pathogenicity, declined in a concentration-dependent manner following the CZEO treatment compared with the control. Thus, CZEO appeared to directly target the pathogenicity MRSA regulators. These findings substantiate the potential of CZEO as a natural antimicrobial agent for preventing MRSA infections. [ABSTRACT FROM AUTHOR]

A highly sensitive light-induced thermoelastic spectroscopy (LITES) sensor employing a charge amplifier (CA) is reported for the first time in this invited paper. CA has the merits of high input impedance and strong anti-interference ability. The usually used transimpedance amplifier (TA) and voltage amplifier (VA) were also studied under the same conditions for comparison. A standard commercial quartz tuning fork (QTF) with a resonant frequency of approximately 32.76 kHz was used as the photothermal signal transducer. Methane (CH4) was used as the target gas in these sensors for performance verification. Compared to the TA-LITES sensor and VA-LITES sensor, the reported CA-LITES sensor shows improvements of 1.83 times and 5.28 times in the minimum detection limit (MDL), respectively. When compared to the LITES sensor without an amplifier (WA-LITES), the MDL has a 19.96-fold improvement. After further optimizing the gain of the CA, the MDL of the CA-LITES sensor was calculated as 2.42 ppm, which further improved the performance of the MDL by 30.3 times compared to the WA-LITES. Additionally, long-term stability is analyzed using Allan deviation analysis. When the average time of the sensor system is increased to 50 s, the MDL of the CA-LITES sensor system can be improved to 0.58 ppm. [ABSTRACT FROM AUTHOR]

Organic field-effect transistors (OFETs) are an ideal platform for intrinsically stretchable sensors due to their diverse mechanisms and unique electrical signal amplification characteristics. The remarkable advantages of intrinsically stretchable sensors lie in their molecular tunability, lightweight design, mechanical robustness, solution processability, and low Young's modulus, which enable them to seamlessly conform to three-dimensional curved surfaces while maintaining electrical performance under significant deformations. Intrinsically stretchable sensors have been widely applied in smart wearables, electronic skin, biological detection, and environmental protection. In this review, we summarize the recent progress in intrinsically stretchable sensors based on OFETs, including advancements in functional layer materials, sensing mechanisms, and applications such as gas sensors, strain sensors, stress sensors, proximity sensors, and temperature sensors. The conclusions and future outlook discuss the challenges and future outlook for stretchable OFET-based sensors. [ABSTRACT FROM AUTHOR]

Ethylene glycol (EG) is a colorless and odorless organic compound, which is an important industrial raw material but harmful to the environment and human health. Thus, it is necessary to develop high-performance sensing materials to monitor EG gas. Herein, sea urchin-shaped ZnO was successfully synthesized by a hydrothermal method. Subsequently, a series of carbon dot (CD)-modified ZnO nanocomposites were successfully prepared using a simple mechanical grinding method. The prepared CDs@ZnO-1 sensor exhibits an excellent response to EG gas, with a response value of 1356.89 to 100 ppm EG at the optimal operating temperature (220 °C). After five cycles of detection, the sensor can still maintain a stable response. The enhanced sensing performance of EG can be attributed to rich oxygen vacancies that are generated on the surface of CDs@ZnO, and the heterojunction formed between p-type CDs and n-type ZnO. This study provides inspiration for the development of high-response semiconductor metal oxide sensors. [ABSTRACT FROM AUTHOR]

Simple Summary: In this work, Y-doped LTO nanosheets were synthesized for NO2 gas sensing under different humidity conditions. These materials showed increased responses at higher humidity levels due to enhanced proton conduction and NO2-assisted proton generation. Notably, Y-doped LTO nanosheets exhibited higher responses than pure LTO, as Y-doping created more oxygen vacancies, improving water adsorption and proton dissociation. Water molecules from the environment or human breath are one of the main factors affecting the accuracy, efficiency, and long-term stability of electronic gas sensors. In this contribution, yttrium (Y)-doped La2Ti2O7 (LTO) nanosheets were synthesized by a hydrothermal reaction, demonstrating improved proton conductivity compared to their non-doped counterparts. The response of Y-doped LTO with the optimal doping concentration to 100 ppm NO2 at 43% relative humidity (RH) was −21%, which is four times higher than that of bare La2Ti2O7. As the humidity level increased to 75%, the response of Y-doped LTO further increased to −64%. Unlike the gas doping effect observed in previous studies of semiconducting metal oxides, the sensing mechanism of Y-doped LTO nanosheets is based on the enhanced dissociation of H2O in the presence of target NO2 molecules, leading to the generation of more protons for ion conduction. This also resulted in a greater resistance drop and thus a larger sensing response at elevated humidity levels. Our work demonstrates that proton-conductive oxide materials are promising gas-sensing materials under humid conditions. [ABSTRACT FROM AUTHOR]

To facilitate the effective assessment of respiratory entropy during poultry breeding, a novel oxygen (O2) and carbon dioxide (CO2) sensor was developed based on the off−axis integrated cavity output spectroscopy technique, featuring effective absorption optical paths of 15.5 m and 8.5 m, respectively. The sensor employs integrated environmental control technology, substantially enhancing detection precision. To improve the instrument's response speed, the miniaturization of the cavity and structural optimization were implemented, achieving a rapid response time of merely 6.22 s, addressing the stringent requirements for quick responsiveness in poultry respiration thermometry research. A signal processing model tailored for on−site applications was designed, boosting the system's signal−to−noise ratio by 4.7 times under complex environmental noise conditions. Utilizing Allan variance analysis, the sensor's detection limits for O2 and CO2 were ascertained to be 2.9 ppm and 7.4 ppb, respectively. A 24−h field application test conducted in Gongzhuling demonstrated that the sensor's results align with the respiratory characteristics of poultry under normal physiological conditions, validating its extensive potential for application in respiratory analysis, environmental monitoring, and industrial sectors. [ABSTRACT FROM AUTHOR]

In this review, we present the last ten years of progress in evaluation of gas sensing mechanisms. We focus mostly on the studies joining theoretical modeling of gas adsorption by density functional theory method with advanced experimental characterization of sensing materials. We provide the background about important aspects that should be taken into account during the design of the effective sensing device and an overview of the most recently studied sensing materials and analytes. Using the exemplary works, we next show how theory and experiment intertwine in revealing how the sensing mechanism serves to improve the device performance. In the end, we summarize the progress already made despite the existing difficulties, and provide an outlook for future methodological development. [ABSTRACT FROM AUTHOR]

Gas sensor-based electronic noses (e-noses) have gained considerable attention over the past thirty years, leading to the publication of numerous research studies focused on both the development of these instruments and their various applications. Nonetheless, the limited specificity of gas sensors, along with the common requirement for chemical identification, has led to the adaptation and incorporation of analytical chemistry instruments into the e-nose framework. Although instrument-based e-noses exhibit greater specificity to gasses than traditional ones, they still produce data that require correction in order to build reliable predictive models. In this work, we introduce the use of a multivariate signal processing workflow for datasets from a multi-capillary column ion mobility spectrometer-based e-nose. Adhering to the electronic nose philosophy, these workflows prioritized untargeted approaches, avoiding dependence on traditional peak integration techniques. A comprehensive validation process demonstrates that the application of this preprocessing strategy not only mitigates overfitting but also produces parsimonious models, where classification accuracy is maintained with simpler, more interpretable structures. This reduction in model complexity offers significant advantages, providing more efficient and robust models without compromising predictive performance. This strategy was successfully tested on an olive oil dataset, showcasing its capability to improve model parsimony and generalization performance. [ABSTRACT FROM AUTHOR]

Over the past few years, more studies have been conducted on the use of photonic crystals (PCs) in the detection field. Particularly fascinating for use as gas sensors are these materials' outstanding spectrum sensitivity and small design. Using one-dimensional PCs as the theoretical foundation, this work aims to develop and analyze a nanoscale system that can identify the concentration of gases in ambient air and differentiate it from contaminated air. The intended structure is composed of layers of gallium nitride (GaN) and aluminum nitride (AlN) that alternate. In between these layers is a defective layer cavity that is filled with polluted air, which has a refractive index that is quite similar to pure air. The transfer matrix method (TMM) was used to perform numerical results for the proposed sensor. This sensor achieves average sensitivity of 1791 nm/RIU, average quality factor and figure of merit (FoM) of 1833 and 2287, respectively. We therefore think that the suggested detector's design offers a strong candidate for accurate and efficient detection. Recent research on photonic crystals (PCs) for gas detection emphasizes their sensitivity and compact design. This study introduces a nanoscale sensor with GaN and AlN layers and a cavity filled with polluted air. Simulations show high sensitivity, suggesting the sensor is a promising tool for efficient gas detection. [ABSTRACT FROM AUTHOR]

A novel quaternary nanocomposite composed of porous boron nitride, β-SiC fibers, SnO2, and In2O3 was successfully synthesized and their interconnection led to effective and highly stable gas sensing. The formation of the newly modeled quaternary nanocomposite enabled the formation of an effective electron transfer pathway and provided a large contact area between the detecting gas and gas sensor material. The physical and chemical properties of the nanocomposites were analyzed using analytical techniques, such as XRD, SEM, TEM-HRTEM, BET, XPS, PL, and Raman techniques. First-principles calculations were performed to evaluate the proportion of states occupied by the system at each energy level. The gas-sensing capabilities of the quaternary nanocomposites were evaluated using CO2 and O2 gas purging at various temperatures. The gas-sensing capabilities of the quaternary nanocomposites were evaluated using CO2 and O2 gas purging at different temperatures. The gas-sensing properties of the β-SiC fiber and the previously studied β-SiC/In2O3/SnO2 were improved by the exceptional electronic conductivity and chemical activity of the pBN/β-SiC/SnO2/In2O3 quaternary nanocomposites. At room temperature, the pBN-105 NCs exhibited the high resistance to O2 gas and a weak response to CO2 gas. However, the sensor exhibited strong sensitivity to both CO2 and O2 gases at high temperatures. In each gas-sensing test, the quaternary nanocomposites exhibited strong resistance and low current density. The effective charge transfer and separation properties, as well as the electron density of the sensor layer of the quaternary nanocomposites, allowed for better sensing under a range of high-temperature variations, while the addition of MOs and porous boron nitride increased the usefulness of the β-SiC fiber. Graphical abstract of the fabrication of the nanostructured pBN/β−SiC fiber/SnO2/In2O3 gas sensor and the CO2/O2 gas sensing mechanism [ABSTRACT FROM AUTHOR]

In this letter, MEMS gas sensors-based electronic nose (e-nose) was developed and used for odorant evaluations at different parts of the city. A gas analyzer, in conjunction with sensorial analysis, was performed for different odorous samples. The design of experiments that consisted of eight experimental sets was developed to the selectivity and sensitivity of the developed sensor array following the actual environmental scenario. Advanced multivariate statistical approaches, such as linear discriminant analyses and K-means, were used to describe sample similarity and discrimination ability of the system. The e-nose data processing exhibits satisfactory discrimination between air samples with more than 97% variability. A validated partial least-square (PLS) model foresees good co-relation between e-nose measurement and gas analyzer analysis. Analysis of variance shows that the model is a good fit with significantly reduced RMSE values and high $R^{2}$ values. The finding indicates that an e-nose unit could be a low-cost solution for environmental measurement-based odorant emissions measurement. [ABSTRACT FROM AUTHOR]

In the modern world, gas sensors play a crucial role in sectors such as high-tech industries, medicine, and environmental monitoring. Among these fields, oxygen sensors are the most important. There are several types of oxygen sensors, including optical, magnetic, Schottky diode, and resistive (or chemoresistive) ones. Currently, most oxygen-resistive sensors (ORSs) described in the literature are fabricated as thick layers, typically deposited via screen printing, and they operate at high temperatures, often exceeding 700 °C. This work presents a novel approach utilizing atomic layer deposition (ALD) to create very thin layers. Combined with appropriate doping, this method aims to reduce the energy consumption of the sensors by lowering both the mass requiring heating and the operating temperature. The device fabricated using the proposed process demonstrates a response of 88.21 at a relatively low temperature of 450 °C, highlighting its potential in ORS applications based on doped ALD thin films. [ABSTRACT FROM AUTHOR]

Gouda-type cheese originated in the Netherlands, but is now produced all over the world. Analogue cheeses are cheese-like products with a lower price level that are based on non-dairy fats and proteins. The market demand for analogue cheese is currently also growing due to customers' preference for low-fat foods. In this report, samples of Gouda-type cheese and its analogues produced by a dairy cooperative (Warmian-Masurian Voivodeship, Poland) were used as the subject of analysis; their volatile profiles were analyzed by gas chromatography coupled with mass spectrometry (GC-MS). In addition, measurements were carried out using a low-cost electronic nose based on MOX sensors. The results showed a richer chemical composition of the cheese volatiles compared to the analogue product. The measurements with the electronic nose made it possible to differentiate between the sample categories but also revealed similarities between them. The research demonstrated that both methods could be used for the assessment of the volatile profiles of the products. [ABSTRACT FROM AUTHOR]

Ammonia, despite being a naturally generated compound in the metabolic process, can be harmful to health in higher concentrations. In this context, sensor devices are directly related to health and safety measurements to detect the presence of such substances. In this work, we study materials derived from fullerene, a material with a high electron affinity. We characterize three fullerene derivatives, namely PCBM, OPCBMMB and PPCBMB, and verify their applicability as ammonia sensors. The materials were studied in the form of thin films, produced by Langmuir–Schaefer and drop‐casting techniques. Optical characterization was performed using UV–visible spectroscopy while morphological characteristics were studied using atomic force microscopy (AFM) and optical microscopy (OM). Current versus voltage and current versus time measurements were performed in order to determine the films' conductivities, electrical resistances and gas‐sensing properties. UV–visible absorption was observed at lower wavelengths, with peaks in the UV region. In the electrical measurements, differences were observed between the deposition techniques, with the Langmuir–Schaefer films showing a higher conductivity than the drop‐casting films. AFM and OM also showed differences in the film surfaces between the techniques, with a rougher surface on the drop‐casting films. When exposed to ammonia, the materials showed electrical responses at every cycle, with a significant increase in their electrical responses. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Zinc Oxide (ZnO) nanoparticles and reduced graphene oxide (rGO) nanosheets were synthesized using the Coprecipitation method and modified Hummer's method, respectively. The nanocomposite of ZnO@rGO was then prepared via the ultrasonication method for NO2 gas sensing and as an electrode material for supercapacitor application. The ZnO@rGO films with different rGO compositions of 12 weight percentage (wt. %) (ZG-12), 15 wt. % (ZG-15), and 18 wt. % (ZG-18) exhibited percentage responses of 46%, 60%, and 51% at room temperature for 10 ppm NO2 gas. Similarly, these composite materials exhibited specific capacitance values of 233, 253, and 207 Fg - 1 , respectively, at a specific current of 0.5 Ag - 1 . Gas-sensing performance was optimized under various conditions (0.5–40 ppm gas concentrations, 25–100 °C temperatures, and 25–100% relative humidity). The sensor demonstrated excellent NO2 gas selectivity, with a detection limit of 0.5 ppm. This ZnO-rGO-based NO2 gas sensor offers a novel, room temperature-operating device with high response, reproducibility, and humidity tolerance. An asymmetric supercapacitor (ASC) device is fabricated using ZG-15 as the cathode and rGO as the anode electrode. This ASC device demonstrates a commendable specific energy density of 5.34 Wh kg−1 and a power density of 2.20 kW kg−1. Moreover, two such devices connected in series successfully illuminate red and green LEDs for over 5 and 3 min, respectively. This work provided successful insight into the multifunctional application of ZnO@rGO composite in the field of gas sensing and energy storage devices. [ABSTRACT FROM AUTHOR]

Hydrogen detection (H2) has become a crucial concern in various industrial and environmental scenarios due to its explosive and highly flammable nature. Recently, there has been a notable focus on sensors based on nanomaterials, owing to their remarkable sensitivity, selectivity, and stability when detecting H2. This article offers an all-encompassing outline of the present cutting-edge status of hydrogen sensors utilizing nanomaterials, particularly concentrating on metal oxides like SnO2, ZnO, TiO2, WO3, NiO, In2O3, and a wide range of other materials. Special attention is paid to exploring the mechanisms involved in hydrogen detection. Furthermore, the review includes a thorough evaluation of the obstacles and possibilities associated with designing and fabricating nanomaterial-driven hydrogen sensors with exceptional performance. The review concludes by highlighting that nanomaterial-based sensors could bring about a revolutionary shift in the realm of hydrogen detection. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Test & Measurement Technology is the property of Publishing Center of North University of China and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Gas sensing materials of niobium doped titanium dioxide (TiO 2) mixed with reduced graphene oxide (rGO) were investigated with the optimized rGO content and niobium doping ratio. Using glycerol (C 3 H 8 O 3) as solvent, rGO/Nb-doped TiO 2 slurry was prepared by mechanical ball milling method, and then the slurry was casted onto the micro-electro-mechanical system (MEMS) gas sensor substrate. With 10% rGO compositing and 0.8% niobium doping, the response of the sensors compare to the undoped 10rGO/TiO 2 sensors, the working temperature of the MEMS hydrogen sensor was successfully brought down to 100 °C, and the response to 1000 ppm hydrogen was 2.5. The rGO/Nb–TiO 2 sensors also demonstrated good stability, ideal repeatability, great selectivity, and a quick response/recovery time of 32.5/51 s. The addition of rGO increased the surface area of the sensing materials, thus increase the adsorption site for H 2. The doping of Nb increased the carrier concentration of TiO 2 , enable TiO 2 to work at lower temperature. The small size of the MEMS sensor allows it to be used in various applications. • MEMS H 2 sensors with small size and high performance have been fabricated. • Nb doping is conducive to the introduction of more oxygen vacancies in TiO 2. • The rGO can provide larger specific surface area and charge transfer to Ti. • The MEMS sensor could be applied to next generation smart living. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2) is one of the most critical gases in transformer oil. In this paper, an H 2 sensor based on spindle-shaped multilateral CeO 2 rods in micron size and TiO 2 quantum dots (QDs) with an average size of 3.09 nm was designed. The sensor based on CeO 2 with 1 wt%TiO 2 has the best performance and is labeled as Ce–Ti1 sensor. The Ce–Ti1 sensor operates at 250 °C and has the better response value of 52.51% to H 2 of 1000 ppm. The response time is less than 1 s for 2000 ppm H 2 and the response time is 1 s. The Ce–Ti1 sensor has low response values for several dissolved gases in transformer oils (5.78 times than 1000 ppm C 2 H 6 , 9.28 times than 50 ppm CO, and 18.04 times than 1000 ppm CH 4). The response of the Ce–Ti1 sensor is affected by humidity, while it shows good long-term stability and repeatability. The response intensity can decrease by 50.21% in RH = 85% compared with sensing performance in RH = 33%. First-principle calculations are used to analyze the H 2 -sensing properties of TiO 2 , CeO 2 , and their composite heterostructures from a microscopic perspective. The adsorption mechanism between the Ce–Ti1 heterojunction and H 2 molecules is analyzed by the adsorbed oxygen mechanism. The construction of DFT calculations and H 2 -sensitive mechanism models can provide guidance for the subsequent construction of high-performance CeO 2 -based gas sensors. Figure. a SEM characterization of Ce–Ti1 composite, b hydrogen sensing mechanism. [Display omitted] • The particle size of TiO 2 quantum dots is 3.09 nm. • The sensor CeTi1 shows sub-second response time (1 s @ 2000 ppm H 2). • DFT is further used to analyze the enhancement effect of TiO 2 QDs. [ABSTRACT FROM AUTHOR]