Improved Sensor Response Research Articles

Optimizing Ammonia Detection with a Polyaniline-Magnesia Nano Composite.

Polyaniline-magnesia (PANI/MgO) composites with a fibrous nanostructure were synthesized via in situ oxidative polymerization, enabling uniform MgO integration into the polyaniline matrix. These composites were characterized using FTIR spectroscopy to analyze intermolecular bonding, XRD to assess crystallographic structure and phase purity, and SEM to examine surface morphology and topological features. The resulting PANI/MgO nanofibers were utilized to develop ammonia (NH3) gas-sensing probes with evaluations conducted at room temperature. The study addresses the critical challenge of achieving high sensitivity and selectivity in ammonia detection at low concentrations, which is a problem that persists in many existing sensor technologies. The nanofibers demonstrated high selectivity and optimal sensitivity for ammonia detection, which was attributed to the synergistic effects between the polyaniline and MgO that enhance gas adsorption. Furthermore, the study revealed that the MgO content critically influences both the morphology and the sensing performance, with higher MgO concentrations improving sensor response. This work underscores the potential of PANI/MgO composites as efficient and selective ammonia sensors, highlighting the importance of MgO content in optimizing material properties for gas-sensing applications.

Universal Murray’s law for optimised fluid transport in synthetic structures

Materials following Murray’s law are of significant interest due to their unique porous structure and optimal mass transfer ability. However, it is challenging to construct such biomimetic hierarchical channels with perfectly cylindrical pores in synthetic systems following the existing theory. Achieving superior mass transport capacity revealed by Murray’s law in nanostructured materials has thus far remained out of reach. We propose a Universal Murray’s law applicable to a wide range of hierarchical structures, shapes and generalised transfer processes. We experimentally demonstrate optimal flow of various fluids in hierarchically planar and tubular graphene aerogel structures to validate the proposed law. By adjusting the macroscopic pores in such aerogel-based gas sensors, we also show a significantly improved sensor response dynamics. In this work, we provide a solid framework for designing synthetic Murray materials with arbitrarily shaped channels for superior mass transfer capabilities, with future implications in catalysis, sensing and energy applications.

Enhancing Sensitivity in Gas Detection: Porous Structures in Organic Field-Effect Transistor-Based Sensors.

Gas detection is crucial for detecting environmentally harmful gases. Organic field-effect transistor (OFET)-based gas sensors have attracted attention due to their promising performance and potential for integration into flexible and wearable devices. This review examines the operating mechanisms of OFET-based gas sensors and explores methods for improving sensitivity, with a focus on porous structures. Researchers have achieved significant enhancements in sensor performance by controlling the thickness and free volume of the organic semiconductor layer. Additionally, innovative fabrication techniques like self-assembly and etching have been used to create porous structures, facilitating the diffusion of target gas molecules, and improving sensor response and recovery. These advancements in porous structure fabrication suggest a promising future for OFET-based gas sensors, offering increased sensitivity and selectivity across various applications.

SnO2 QDs sensitized ZnFe2O4 spheres with enhanced acetone sensing performance

Herein, SnO2 QDs (<10 nm) with small size instead of conventional nanoparticles was employed to modify ZnFe2O4 to synthesize porous and heterogeneous SnO2/ZnFe2O4 (ZFSQ) composites for gas sensing. By an immersion process combined with calcination treatment, the resultant porous ZFSQ composites with different contents of SnO2 QDs were obtained, and their sensing properties were investigated. Compared with bare ZnFe2O4 and SnO2 QDs, porous ZFSQ composites based-sensors showed much improved sensor response to acetone. For contrast, the sensor performance of ZFSQ composites was also compared with that of ZnFe2O4 sphere modified by SnO2 nanoparticles with different size. The porous ZFSQ composite with 5 wt% SnO2 QDs (ZFSQ-5) showed a better acetone sensing response than that of other ZFSQ composites, and it exhibited a high response value of 110–100 ppm of acetone and a low detection limit of 0.3 ppm at 240 °C. In addition to the rich heterojunctions and porous structure, the size effect of SnO2 QDs was other indispensable reasons for the improved sensor performance. Finally, the ZFSQ-5 composite sensor was attempted to be applied for acetone sensing in exhaled breath, suggesting its great potential in monitoring acetone.

Preparation and performance of TiO2/ZnO humidity sensor based on TiO2

In this study, TiO2 was selected as the primary material to prepare a humidity sensor. To enhance its sensing performance, it was doped with ZnO, and a TiO2/ZnO composite was synthesized via the hydrothermal method. Based on this composite material, a TiO2/ZnO humidity sensor was designed and fabricated. The sensor properties were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) techniques. The increase in hydroxyl and oxygen vacancy content on the surface of composite materials enhances their sensitivity to water molecules, leading to improved sensor response. The construction of ZTO3 heterojunction promotes the migration of electrons on the sensor surface to improves the performance of the sensor. Humidity sensor based on the TiO2/ZnO composite material exhibits excellent performance, with high response to water molecules, a fast response/recovery time (18/22 s), low humidity hysteresis (1.55 %), and low interference from monochromatic light. Thus, the TiO2-based humidity sensor doped with ZnO shows great potential for practical applications.

Gold Sensitized In2O3 nanocubes for ppb level NO2 gas sensing

Hydrothermally synthesized In2O3 nanocubes were sensitized with Au and gas sensing performance is analyzed. The Au sensitization was done using sputtering and gas sensing performance is studied as function of different sputtering time. The catalytic activity of Au particles on In2O3 films increases with the sputtering time but acquires saturation at high sputtering time. The Au sensitization with sputtering time of 5 s was found to show improved sensor response (Rg/Ra) of 8435 than the sensor response of 6876 for pure In2O3 film. The improved sensor response was attributed to the catalytic activity of Au particles on the In2O3 film surface. In addition, Au sensitized In2O3 also demonstrates the sensor response at 60 ppb.

Synergistic Effect of TiS3 and Ti3C2Tx MXene for Temperature-Tunable p-/n-Type Gas Sensing

We propose a strategy for highly tunable gas sensors, in which a MXene is combined with a sacrificial material that could be controllably oxidized upon mild annealing to form oxide nanoparticles that alter the sensing response. A controlled annealing of such composite generally retains the integrity of MXene sheets while gradually converting the sacrificial material to a metal oxide that could form semiconductor heterojunctions with MXene, fine-tuning its sensor properties. This strategy is demonstrated using gas sensors based on Ti3C2Tx MXene mixed with TiS3, a semiconducting transition metal trichalcogenide. Compared to pristine MXene, the Ti3C2Tx-TiS3 composite exhibited a significantly improved sensor response to ethanol, which served as a model analyte, both at room temperature and upon annealing. Furthermore, as a less thermally stable material than the MXene, TiS3 oxidizes faster than Ti3C2Tx at elevated temperatures, producing TiO2 nanoparticles that strongly affect the sensing response. A pristine Ti3C2Tx exhibits a p-type sensor response to ethanol at room temperature. Upon annealing, Ti3C2Tx gradually degrades to TiO2, changing the sensor response to n-type above ∼300 °C. The addition of TiS3 allows for the general preservation of MXene as the sensor material, as the temperature of the p–n transition decreases to about 200 °C, at which Ti3C2Tx is generally stable. This approach can likely be applied to a great variety of combinations of various MXenes and sacrificial compounds with sensor properties that could be tuned via annealing for specific analytes or applications.

Selective detection of Cd (II) and Cr (VI) ions using rGO functionalized metal doped SnO2 nanocomposites

This research gives a valuable insight for understanding the effect of doping on morphology and rGO functionalization on electrochemical sensing. Firstly, hydrothermal method was used to synthesize pure SnO2, cobalt (Co) doped and iron (Fe) doped SnO2 nanocomposites. Doping of Co/Fe into SnO2, gradually attract spherical nanoparticles together to form a three-dimension cube-like structure. Considering the potential of these morphological changes, their heavy metal ions (HMIs) sensing properties have been further investigated. The results revealed that the type of dopants (Co/Fe) and their morphologies have a significant impact on the HMIs sensing performance. 1 wt% doping of Co and Fe into SnO2 shows highest selectivity (∼2.3 – 8.4 (Co doping); ∼2–13 (Fe doping)) and sensitivity (∼1.4 µA/ppb (Co doping); ∼2.6 µA/ppb (Fe doping)) toward cadmium (Cd (II)) and chromium (Cr (VI)) ions respectively as compared to other HMIs. Furthermore, reduced graphene oxide (rGO) functionalized Co doped and Fe doped SnO2 nanocomposites were synthesized using ultrasonication method. The rGO functionalized metal doped nanocomposites improve HMIs sensing performance than pure and metal doped SnO2 nanocomposites. According to electrochemical studies, the synthesis of nanocomposites with strong electrocatalytic activity and enhanced active surface area is primarily responsible for improved sensor response.

Noise spectroscopy based numerical modelling of chemisorption on SnO2 surface for CO gas sensing applications

The gas sensor response of the tin oxide (SnO2) semiconductor toward carbon monoxide (CO) gas has been simulated using the noise spectroscopy technique. The Wolkenstein gas adsorption model is used to calculate the surface coverage of environmental oxygen ions and target gas molecules. The interaction of CO gas molecules with the negatively charged oxygen ions has been incorporated in the numerical model. The equilibrium charge neutrality condition of the semiconductor material has been solved as a function of gas adsorption parameters like surface coverage, temperature, pressure and surface potential. Eventually, the power density spectrum (PDS) of the electrical conductance of the sensing layer was calculated before and after the gas adsorption conditions. It has been observed that the semiconductor band bending increases sharply at a certain concentration of environmental oxygen gas concentration (10−4 to 10−3 atm). At a temperature of 480 K, a steep decrease in surface potential was observed. This temperature range of maximum sensor response was optimized for calculating noise spectrum of electrical conductivity fluctuations at equilibrium condition of adsorption-desorption. The cutoff frequency (109 Hz) was calculated using normalized PDS of electrical conductance. The gas sensor response was calculated as a ratio of film conductance before and after the gas adsorption as a function of gas pressure and surface temperature at the calculated cutoff frequency. The increase in sensor response was observed with the increase in CO partial pressure as a function of temperature for a specific cut off frequency. The comparison of sensor response of the presented model has been demonstrated with another published numerical model. The presented model shows improved sensor response for higher (>10−8 atm) CO partial pressure.

Synthesis of 1D SnO2 nanorods / 2D NiO porous nanosheets p-n heterostructures for enhanced ethanol gas sensing performance

The microstructure and composition of materials have significant impacts on the gas sensing performance of sensors. In this work, a well-constructed 1D SnO2 nanorods/2D NiO porous nanosheets heterostructure were successfully prepared for the detection of ethanol gas. The SnO2 nanorods with a diameter of 10–15 nm uniformly grew on the surface of NiO nanosheets, increasing the number of active sites. The space charge region formed at heterointerfaces controlled electron transfer, benefiting for improving sensor response. Gas test results showed that, at the optimum operating temperature of 300 °C, NiO/SnO2 (Ni:Sn = 1:0.5) reached a high response of 25.7 to 100 ppm ethanol, which was about 15 times higher than pure NiO (1.65). In addition, the NiO/SnO2 displayed a fast response-recovery speed, good selectivity, and excellent long-term stability. The enhanced gas sensing mechanism of NiO/SnO2 was proposed by analyzing the surface chemical states, surface area, and electronic structure of materials.

Self-Assembled 1-Octadecanethiol Membrane on Pd/ZnO for a Selective Room Temperature Flexible Hydrogen Sensor.

A layer of self-assembled 1-octadecanethiol was used to fabricate a palladium (Pd)/zinc oxide (ZnO) nanoparticle-based flexible hydrogen sensor with enhanced response and high selectivity at room temperature. A palladium film was first deposited using DC sputtering technique and later annealed to form palladium nanoparticles. The formation of uniform, surfactant-free palladium nanoparticles contributed to improved sensor response towards hydrogen gas at room temperature. The obtained sensor response was higher than for previously reported room temperature Pd/ZnO sensors. Furthermore, the use of the polymer membrane suppressed the sensor’s response to methane, moisture, ethanol, and acetone, resulting in the selective detection of hydrogen in the presence of the common interfering species. This study shows a viable low-cost fabrication pathway for highly selective room temperature flexible hydrogen sensors for hydrogen-powered vehicles and other clean energy applications.

Recent Advancement for the Synthesis of MXene Derivatives and Their Sensing Protocol

AbstractThe highly efficient, 2D material‐based sensing devices are well‐suited with the advanced production technology which provide the data that can be applied effectively for the monitoring of environmental and health‐related problems. Recently, MXenes considered as new blood in the form of 2D transition metal carbides (TMC), transition metal nitride or transition metal carbonitrides that are added first time to 2D nanomaterials family MXene which are compounds obtained as a result of chemical delamination of quaternary or (ternary) layered nitrides or carbides found as an outstanding member of 2D elemental materials. On behalf of rich chemistries and unique morphologies, the MXenes derivatives delivered efficient sensors, energy storage, catalysis, and water purification. The superior volumetric surface area provides improved sensor response and greater optic, electrical, and magnetic characteristics, which are important advantages in biological and biomedical applications over macroscale materials. In this review article, different synthetics strategies of Mxene derivatives are organized and discuss their availability in terms of caste, yield, physical properties, and simplicity. To keep in mind, the facile synthetic approach and stable physical properties, the Ti3C2Tx Mxene is chosen as a model Mxene derivative, and its application in the field of environmental and biological sensors is discussed in detail.

Free-standing, thin-film sensors for the trace detection of explosives

In a world focused on the development of cybersecurity, many densely populated areas and transportation hubs are still susceptible to terrorist attacks via improvised explosive devices (IEDs). These devices frequently employ a combination of peroxide based explosives as well as nitramines, nitrates, and nitroaromatics. Detection of these explosives can be challenging due to varying chemical composition and the extremely low vapor pressures exhibited by some explosive compounds. No electronic trace detection system currently exists that is capable of continuously monitoring both peroxide based explosives and certain nitrogen based explosives, or their precursors, in the vapor phase. Recently, we developed a thermodynamic sensor that can detect a multitude of explosives in the vapor phase at the parts-per-trillion (ppt) level. The sensors rely on the catalytic decomposition of the explosive and specific oxidation–reduction reactions between the energetic molecule and metal oxide catalyst; i.e. the heat effects associated with catalytic decomposition and redox reactions between the decomposition products and catalyst are measured. Improved sensor response and selectivity were achieved by fabricating free-standing, ultrathin film (1 µm thick) microheater sensors for this purpose. The fabrication method used here relies on the interdiffusion mechanics between a copper (Cu) adhesion layer and the palladium (Pd) microheater sensor. A detailed description of the fabrication process to produce a free-standing 1 µm thick sensor is presented.

Surface Modification of ZnO Nanowires with CuO: A Tool to Realize Highly-Sensitive H2S Sensor

Hydrothermally grown ZnO nanowires (NWs) have been successfully synthesized and surface modified by an ultrathin layer of CuO using dip coating technique to achieve a highly sensitive H2S sensor. XRD analysis confirmed the hexagonal structure of ZnO without any Cu sub-oxide peaks. After CuO modification, the peak shift was observed in the electronic states of O and assigned to the defects and increase in adsorbed oxygen species. Similarly, a red shift was also observed in the band edge absorption after CuO modification arising due to defects. The sensor film showed an overall n-type character as confirmed using I(V) characteristics. Interestingly, sensor response kinetics towards H2S were enhanced after CuO modification. The highest sensor response value of 298 was measured towards 10 ppm H2S at 150°C for CuO:ZnO NWs sample having 1.26 at % of Cu. This improved sensor response has been attributed mainly to the formation of randomly distributed p–n nano-hetero-junctions between p-type CuO and n-type ZnO over the sensor surface. In particular, the p–n nano-hetero-junctions collapsed due to conversion of semiconducting CuO into metallic CuS after the unique interaction with H2S.

Selective ppb-level NO2 gas sensor based on SnO2-boron nitride nanotubes

Abstract This paper demonstrated a hybrid SnO2–BNNTs (SnO2 decorated boron nitride nanotubes) for trace ppb-level sensing towards NO2. A facile way is utilized for the synthesis of SnO2–BNNTs in which BNNTs are consistently coated with SnO2 nanoparticles (NPs). The existence of SnO2 NPs onto BNNTs was confirmed by XRD, XPS, FESEM, and TEM. Sensing characteristics of SnO2–BNNTs sensor, including the sensor response, repeatability, long-term stability, and response–recovery times were studied by exposure to several NO2 gas concentrations varying from 250 ppb to 5 ppm at different operating temperatures form 25 °C–300 °C. As a result, the SnO2–BNNTs sensor showed an extremely low detection limit (DL) of 250 ppb, as well as a better sensor response as compared to the SnO2 sensor. The maximum sensor response of SnO2–BNNTs sensor was ∼2610 towards 5 ppm NO2 gas at low operating temperature (100 °C). Expanded variation of space charge depleted regions was created at p-n heterojunction which promoted tunneling effect caused by entrapment of NO2 gas molecule and offered conducting channels (CCs) through BNNTs for charge carriers towards an improved sensor response of SnO2–BNNTs sensor.

Exploring the response of a resistive soot sensor to AC electric excitation

The resistive particulate matter sensor is a simple device that transduces the presence of soot through impedance change across inter-digital electrodes (IDEs). We investigate the information provided by impedance spectroscopy over the frequency range from 100 Hz to 10 kHz for two purposes. The first is to investigate the opportunities for an improved sensor response to particulate matter (PM), based on the additional information provided by the measurement of both the in-phase (resistive) and out-of-phase (capacitive) components of the change in impedance over this frequency range as compared to DC resistance measurement only. Secondly, the origin of the capacitive response of the device is investigated from the perspective that soot on the device is in the form of bendable dendrites that grow in three dimensions. An IDE structure with the housing acting as an additional suspended electrode for introducing a controllable vertical electric field component has been used for this purpose. The formation of dipoles, due to bending of the charged dendrites, is found to be the source of the capacitive response. Simulation of electrostatic soot deposition reinforces dendritic self-assembly mechanisms, driven by charged particle trajectories along electric field lines. Optical microscopy confirms that dendrites growing out of the substrate plane are sensitive to electric and flow forces, bending when force balances are appropriate. We also apply impedance spectroscopy under varying electric field strengths, showing that capacitive response is only observed when conditions are conducive to dendrite bending in response to the applied AC electric fields.

Highly Porous Double-Shelled Hollow Hematite Nanoparticles for Gas Sensing

Multishelled hollow micro/nanostructures hold great potential for a variety of important applications due to their fascinating properties. However, the synthesis of multishelled hollow micro/nanostructures mainly relies on template-involved methods. A template-free protocol for multishelled hollow structures remains quite challenging. In this work, a solution strategy based on inside-out and outside-in Ostwald ripening is developed to manipulate hematite hollow spheres with single or double shells without using any hard or soft templates. The structure evolution of the hematite hollow spheres is comprehensively studied to reveal the formation mechanism. As a potential application, the hematite hollow spheres have been utilized for chemical gas sensors to investigate the structure–property correlations. Results demonstrate that the double-shelled hematite spheres exhibit much higher response than the single-shelled ones due to structure sensitization. An improved sensor response is further obtained by cata...

Pulse-Driven Semiconductor Gas Sensors Toward ppt Level Toluene Detection.

Improvements in the responses of semiconductor gas sensors and reductions in their detection limits toward volatile organic compounds (VOCs) are required in order to facilitate the simple detection of diseases, such as cancer, through human-breath analysis. In this study, we introduce a heater-switching, pulse-driven, micro gas sensor composed of a microheater and a sensor electrode fabricated with Pd-SnO2-clustered nanoparticles as the sensing material. The sensor was repeatedly heated and allowed to cool by the application of voltage to the microheater; the VOC gases penetrate into the interior of the sensing layer during its unheated state. Consequently, the utility factor of the pulse-driven sensor was greater than that of a conventional, continuously heated sensor. As a result, the response of the sensor to toluene was enhanced; indeed, the sensor responded to toluene at levels of 1 ppb. In addition, according to the relationship between its response and concentration of toluene, the pulse-driven sensor in this report can detect toluene at concentrations of 200 ppt and even lower. Therefore, the combination of a pulse-driven microheater and a suitable material designed to detect toluene resulted in improved sensor response, and facilitated ppt-level toluene detection. This sensor may play a key role in the development of medical diagnoses based on human breath.

Novel Route for Fabrication of ZnO nanorods-Au Nanoparticles Hybrids Directly Supported on Substrate and their Application as Gas Sensors

The aim of this study was to develop a novel, simple and fast route to prepare ZnO nanorods (NRs) -Au nanoparticles (NPs) hybrids directly supported on a substrate to be used in gas sensor devices. The ZnO NRs were promptly grown on interdigitated Au electrodes Al2O3 substrates by chemical bath deposition at a low temperature. After that, Au NPs were deposited by sputtering. Results obtained by XRD, SEM, EDX and TEM showed the perpendicularly aligned growth of the ZnO NRs with a hexagonal base on the substrate and the Au NPs homogeneously covered the ZnO NRs surface. The ZnO NRs-Au NPs hybrids-based sensor exhibited an improved sensor response for H2 and O2 gases compared to the ZnO NRs at 300 oC. Due to the ability to prepare homogeneous hybrids with high surface directly supported on the substrate; the developed route might provide a convenient approach to preparing gas sensor devices.

Improving sensor response using reduced graphene oxide film transistor biosensor by controlling the adsorption of pyrene as an anchor molecule

Reduced graphene oxide (rGO) films functionalized with linker molecules that bind specific antibodies to the surface of their films are useful for biosensors based on field-effect transistors. Controlling the density of linker molecules on the rGO channel surface is a crucial issue for improving the sensor structure with the desired sensitivity and stability. In this study, ultraviolet–visible (UV–vis) absorption spectroscopy was utilized for the evaluation of the density of linker molecules adsorbed on the rGO and GO surfaces. We revealed that the density of adsorbed linker molecules on the rGO surface is dominated by oxygen-containing groups slightly remaining on the surfaces, rather than the restoration of the π-conjugated system in the graphitic structure of rGO films. We demonstrate that the difference in the density of adsorbed linker molecules on the rGO films significantly affects the sensitivity of sensor responses.