Catalytic Sensor Research Articles

Effect of p- or n-Type Semiconductor on CO Sensing Performance of Catalytic Combustion-Type CO Gas Sensor with CeO2-ZrO2-ZnO Based Catalyst

Abstract Novel catalytic combustion-type CO gas sensors were successfully devised by applying precious metal-free catalysts composed of the p- or n-type semiconducting Ln2CuO4-loaded CeO2-ZrO2-ZnO (Ln2CuO4/CZZn; Ln = La, Nd, and Sm). Complete CO oxidation using the p-type semiconducting La2CuO4/CZZn catalyst occurred at 350 °C, while the n-type semiconducting Nd2CuO4/CZZn and Sm2CuO4/CZZn catalysts completely oxidized CO gas at 220 °C and 200 °C, respectively. All the fabricated sensors exhibited quantitative detection of CO gas over 250 °C. The La2CuO4/CZZn catalyst has the smallest heat capacity, which dramatically increases the Pt coil temperature compared with the other catalysts, resulting in the highest sensor signal. However, the sensor applying Nd2CuO4/CZZn and Sm2CuO4/CZZn catalysts exhibited faster response time to CO gas than the sensor employing La2CuO4/CZZn catalyst due to their superior CO oxidation activity.

Multi-shaped cationic gold nanoparticle-l-cysteine-ZnSeS quantum dots hybrid nanozyme as an intrinsic peroxidase mimic for the rapid colorimetric detection of cocaine

Current presumptive tests for illicit drugs can suffer from false positive results and poor selectivity, and consequentially there is a need to develop new colour spot tests specifically designed to circumvent these existing challenges. In this work, we report on a new fluorescent hybrid nanozyme peroxidase-like catalytic colorimetric sensor and demonstrate proof of concept of this novel colorimetric-specific presumptive test for cocaine. A novel peroxidase-mimic hybrid nanozyme was developed based on the localized surface plasmon resonance-enhanced fluorescence interaction between multi-shaped cationic cetyltrimethylammonium bromide (CTAB)-functionalized gold nanoparticles (AuNPs) and anionic non-cadmium fluorescent-emitting L-cysteine-capped ZnSeS alloyed quantum dots (QDs). The affinity-based interaction of cocaine with the QDs-CTAB-AuNP surface was induced by its distinct structural conformation and this forms the basis for the selective recognition. Thus, the hybrid nanozyme could function both as a catalytic affinity-based receptor and as an optical signal transducer based on the catalysed oxidation of 3,5,5-tetramethylbenzidine by H2O2. A positive bluish-green colour, specific to cocaine recognition, was colorimetrically obtained under optimum catalytic conditions. The optimized assay system detected cocaine within two minutes with unique specificity and distinct colour reaction. Under the optimum cocaine reaction conditions, the analysis of other substances and drugs on the colorimetric response of the QDs-CTAB-AuNP hybrid nanozyme revealed no colour interference, thus demonstrating that the developed probe could be utilized as a presumptive colour spot test for cocaine.

Fluorescence Based Investigation of Temperature-Dependent Pb2+-Specific 8-17E DNAzyme Catalytic Sensor.

The 8-17E DNAzyme is a temperature-dependent DNA metalloenzyme catalyzing RNA trans esterification in the presence of Pb2+ metal ions. Labeling the stems of the substrate and DNAzyme with the Cy3 and Cy5 respectively, the considered DNAzyme was studied by the fluorescence spectroscopy. The temperature-dependent variability of the Pb2+-specific 8-17E DNAzyme catalytic sensor was investigated trough a number of successive temperature fluctuations from 4 to 25°C to obtain information. Investigating underlined biochemical system reveals that in this sensor, free single strands Enzyme (Cy5-E) and Substrate (Cy3-S) have higher fluorescence intensities than hybridized forms, suggesting that the fluorophores are in a contact quenched. Increasing the temperature has three effects: 1) Fluorescence intensities for the free fluorophores were reduced, 2) stability of the hybridized form was reduced and cleavage of substrate in presence of Pb2+was occurred, and 3) conformation of ES hybridized form was changed (before cleavage). As a result of conformation changes in ES, S was more affected than E in the ES. Pb2+ ion shows quenching effect on both fluorophores and in the absence of N2(g) purge the effect was more considerable. A main goal that we had in mind was to find if significantly lower concentrations of Pb2+ and ES, compared to previous reports, can generate any observable cleavage in substrate. Analysis of the cleavage reaction for 50nM ES indicates that S is cleaved at 25°C in presence of N2(g) and 0.5μM Pb2+, while in same condition no apparent change occurs in the 4 or 10°C. The rapid, sensitive and low cost strategy presented here can be applicable to study temperature-dependent behavior of other nucleic acid-based biosensors.

English

English

A Novel Fabricating Process of Catalytic Gas Sensor Based on Droplet Generating Technology.

Catalytic gas sensors are widely used for measuring concentrations of combustible gases to prevent explosive accidents in industrial and domestic environments. The typical structure of the sensitive element of the sensor consists of carrier and catalyst materials, which are in and around a platinum coil. However, the size of the platinum coil is micron-grade and typically has a cylindrical shape. It is extremely difficult to control the amount of carrier and catalyst materials and to fulfill the inner cavity of the coil, which adds to the irreproducibility and uncertainty of the sensor performance. To solve this problem, this paper presents a new method which uses a drop-on-demand droplet generator to add the carrier and catalytic materials into the platinum coil and fabricate the micropellistor. The materials in this article include finely dispersed Al2O3 suspension and platinum palladium (Pd-Pt) catalyst. The size of the micropellistor with carrier material can be controlled by the number of the suspension droplets, while the amount of Pd-Pt catalyst can be controlled by the number of catalyst droplets. A bridge circuit is used to obtain the output signal of the gas sensors. The original signals of the micropellistor at 140 mV and 80 mV remain after aging treatment. The sensitivity and power consumption of the pellistor are 32 mV/% CH4 and 120 mW, respectively.

Neutral reactive gaseous species in reactors suitable for plasma surface engineering

Neutral reactive gaseous species are often major reactants in plasma reactors suitable for tailoring surface properties of materials with weakly ionized gaseous plasma. The density of such species depends on discharge parameters as well as the properties of treated materials. Cylindrical pots made from copper, stainless steel and Teflon were mounted in a reactor of volume 20 l and the density of O-atoms was measured with a laser-heated fiber-optic catalytic sensor. The distribution of O-atoms at different distances from the pots as well as inside the pots was determined at a constant discharge power and different pressures between 30 Pa and 90 Pa. Gradients up to the value of about 2 × 1020 m−3 per centimeter were observed inside the pots. For the case of the metallic samples, the gradients were about twice as high as in the case of Teflon. The resultant density of O-atoms inside the pots dropped for almost an order of magnitude as compared to the value measured in unperturbed plasma, although glowing plasma spread inside the pots. The results were explained by heterogeneous surface recombination of O-atoms to parent molecules. The rather unexpectedly large gradients for the case of Teflon were explained by modification of the surface structure upon synergistic effects of O-atoms and hard UV radiation.

Fabrication and Characterizations of Catalytic Methane Sensor Based on Microelectromechanical Systems Technology

Fabrication and Characterizations of Catalytic Methane Sensor Based on Microelectromechanical Systems Technology

A New Pellistor-Like Gas Sensor Based on Micromachined CMOS Transistor

A new generation of thermal sensors based on a suspended thermal transistor MOS (TMOS), fabricated in the standard CMOS-SOI process, released by postetching, has been recently developed. One of the important features of TMOS is its high responsivity due to the transistor built-in amplification and subthreshold operation enabling a wide range of battery applications. This paper focuses on a new gas sensor, dubbed GMOS, based on the TMOS. The GMOS is a catalytic gas sensor (pellistor-like), and as such detects combustible gases in air. The CMOS-SOI technology combined with tungsten metallization enables operation at very high temperatures (450 °C was tested). The sensors and readout are processed with the same CMOS-SOI technology. Accordingly, the GMOS sensor, processed in low-cost CMOS-SOI technology, promises to become the widely accepted gas sensing approach for mobile applications, including wearables, smart homes, as well as smartphones.

Modelling the Exhaust Gas Aftertreatment System of a SI Engine Using Artificial Neural Networks

In this paper recurrent neural networks are used for modelling of the exhaust gas aftertreatment system of a spark-ignition engine including a three-way catalytic converter and oxygen sensors. Different network architectures are compared based on their achieved mean squared error. We find that physically inspired architectures surpass naive architectures built without knowledge of the physical system. The best resulting model is evaluated by giving the quantiles of the absolute error.

Sensitivity enhancement of catalytic combustion-type CO gas sensor using an artificial diamond with Pt-loaded CeO<sub>2</sub>–ZrO<sub>2</sub>–ZnO based catalyst

Sensitivity enhancement of catalytic combustion-type CO gas sensor using an artificial diamond with Pt-loaded CeO<sub>2</sub>–ZrO<sub>2</sub>–ZnO based catalyst

Fabrication and characterizations of SAW methane sensor based on cryptophane-E membrane

Since the current mining catalytic combustion-type methane sensor is not a detection device used at normal temperature, it is found to have such problems under high temperature conditions (> 450 °C) as poor thermal stability, frequent calibration, short service life and high power consumption. To this end, this paper has studied a room temperature working device that uses cryptophane-E as gas sensitive material, that is, SAW methane sensor. The “three-step approach” is adopted to prepare cryptophane-E material and characterize HUMR and SEM. COMSOL software is used to simulate the rationality of the parameter design of the delay linetype SAW methane sensor. Electron beam exposure photoresist method is used to prepare interdigital electrode on the quartz substrate and form the delay linetype SAW devices, and sensitive materials are loaded using the dispensing method. A sensor performance test system is set up to measure the sensor’s response characteristics at the concentration of 0–5%CH4 using nitrogen as carrier gas. The study shows that the sensor has good response recovery performance within the test concentration range, and the frequency offset is positively correlated with methane concentration; the sensor’s 90% response time is 50 s, 90% recovery time is 72 s, and the sensor sensitivity is 118.8 Hz ± 5 Hz/(1%CH4). The study provides a reference for the development of a new SAW methane sensor, but the temperature and humidity effects and gas selectivity have yet to be further studied.

Laser methane sensor and its field application in coal mine safety

Based on the principle of laser absorption spectroscopy, a laser methane sensor for mine use has been developed. The design of the sensor system is discussed and its practical application for methane detection in coal mines is considered. A control system coupled to the sensor has been developed and the results obtained show the high quality of the performance of the laser methane sensor over the traditional catalytic combustion sensor and infrared sensor in many performance aspects, such as large range, high precision and low power consumption

Natural Sugar: A Green Assistance To Efficiently Exfoliate Inorganic Layered Nanomaterials.

We have demonstrated that natural sugars can efficiently exfoliate inorganic layered nanomaterials with direct stirring. The representative transition-metal dichalcogenides (MoS2 and WS2), transition-metal oxide (MoO3), and graphene were explored, and the formation of ultrathin nanosheets was verified. Glucose and MoS2 selected each other as the perfect partner with superior exfoliation and excellent properties. The obtained inorganic layered nanosheets possess favorable stability and dispersity, which renders it suitable for direct homogeneous liquid applications, such as catalytic activities and sensors. With a high-throughput and green process, the sugar-assisted method may offer new ideas for inorganic layered nanomaterials synthesis and applications in a more ecofriendly way.

Fibre optic sensors for coal mine hazard detection

A number of health and safety hazards present in underground coal mines, which include methane gas explosion, coal combustion, rock roof collapse, and flooding etc. Methane gas and coal combustion have been two major hazards, which resulted in most of the heavy casualties and economic losses. Conventional catalytic methane gas sensors suffer from poor accuracy and cumbersome maintenance, which is the bottleneck of methane hazard prevention. Coal mine combustion monitoring has been relying on gas tubing bundles system, which suffers from long time delay and poor reliability. Semiconductor laser diode methane gas sensors have been developed which has low power consumption, 0–100% full detection range and high accuracy, and no need of recalibration. Fibre optic Raman distributed sensors have been deployed in coal mine goaf and successfully detected combustion hazard in early phase. The FOS-based mine hazard detection system offers unique advantages of intrinsic safety, multi-location and multi-parameter monitoring. The application of FOS on monitoring of methane, coal combustion, micro-seismic and equipment condition are described, future trend of research in this area is also discussed.

A catalytic and dual recycling amplification ATP sensor based on target-driven allosteric structure switching of aptamer beacons

Abnormal concentrations of ATP are associated with many diseases and cancers, and quantitative detection of ATP is thus of great importance for disease diagnosis and prognosis. In the present work, we report a new dual recycling amplification sensor integrated with catalytic hairpin assembly (CHA) to achieve high sensitivity for fluorescent detection of ATP. The association of the target ATP with the aptamer beacons causes the allosteric structure switching of the aptamer beacons to expose the toehold regions, which hybridize with and unfold the fluorescently quenched hairpin signal probes (HP1) to recycle the target ATP and to trigger CHA between HP1 and the secondary hairpin probes (HP2) to form HP1/HP2 duplexes. Due to the recycling amplification, the presence of ATP leads to the formation of many HP1/HP2 duplexes, generating dramatically amplified fluorescent signals for sensitive detection of ATP. Under optimal experimental conditions, our sensor linearly responds to ATP in the range from 25 to 600nM with a calculated detection limit of 8.2nM. Furthermore, the sensor shows a high selectivity and can also be used to detect ATP in human serums to realize its application for real samples. With the distinct advantage of significant signal amplification without the involvement of any nanomaterial and enzyme, the developed sensor thus holds great potential for simple and sensitive detection of different small molecules and proteins.

Methods and algorithms of control catalytic bead type sensor hydrogen

Methods and algorithms of control catalytic bead type sensor hydrogen

Estimation of a Gas Mixture Explosion Risk by Measuring the Oxidation Heat Within a Catalytic Sensor

Combustible gas mixtures and flammable vapors are present in the operating environments of many industries. Detection of the presence of these combustible gases and vapors and assessment of the explosion hazard is of vital importance to ensure that mitigation of the potential hazard can occur before an explosive concentration is reached. In this work, we introduce a gas mixture explosion risk estimation technique for a catalytic sensor. The contribution of this work is threefold. First, we propose the idea of explosion estimation of unknown gas mixtures, which are based on the measurement of heat dissipated during the mixture oxidation at a slow rate. Second, the analysis of transient oxidation processes and sensor response is performed for devising the associated computational scheme to be implemented in a low-power microcontroller. Third, we implement the proposed computational scheme in a wireless sensor node and carry out experiments with various gas mixtures for demonstrating the feasibility of our approach. Combustible heat of gas mixtures of methane, propane, butane, and hydrogen were studied at various concentrations in the range of 28%–56% lower explosive limit. The measurement procedure takes 8.5 s.

Unmanned Aerial Systems for Monitoring Trace Tropospheric Gases

The emission of greenhouse gases (GHGs) has changed the composition of the atmosphere during the Anthropocene. Accurately documenting the sources and magnitude of GHGs emission is an important undertaking for discriminating the contributions of different processes to radiative forcing. Currently there is no mobile platform that is able to quantify trace gases at altitudes <100 m above ground level that can achieve spatiotemporal resolution on the order of meters and seconds. Unmanned aerial systems (UASs) can be deployed on-site in minutes and can support the payloads necessary to quantify trace gases. Therefore, current efforts combine the use of UASs available on the civilian market with inexpensively designed analytical systems for monitoring atmospheric trace gases. In this context, this perspective introduces the most relevant classes of UASs available and evaluates their suitability to operate three kinds of detectors for atmospheric trace gases. The three subsets of UASs discussed are: (1) micro aerial vehicles (MAVs); (2) vertical take-off and landing (VTOL); and, (3) low-altitude short endurance (LASE) systems. The trace gas detectors evaluated are first the vertical cavity surface emitting laser (VCSEL), which is an infrared laser-absorption technique; second two types of metal-oxide semiconductor sensors; and, third a modified catalytic type sensor. UASs with wingspans under 3 m that can carry up to 5 kg a few hundred meters high for at least 30 min provide the best cost and convenience compromise for sensors deployment. Future efforts should be focused on the calibration and validation of lightweight analytical systems mounted on UASs for quantifying trace atmospheric gases. In conclusion, UASs offer new and exciting opportunities to study atmospheric composition and its effect on weather patterns and climate change.

Transient model of oxygen-starved proton exchange membrane fuel cell for predicting voltages and hydrogen emissions

Transfer (crossover) leaks initiated by the chemical deterioration of the PEM and the resulting performance degradation has been previously identified as one the primary life-limiting factors in fuel cells. The leaks result in reduced oxygen levels in affected cells, where a secondary factor intimately related to this is high hydrogen emissions in the cathode exhaust when some cells operate in fully-oxygen-starved conditions. This paper builds on previous work that developed a unified fuel cell model that predicts cell voltage behavior under driving (normal) and driven (oxygen-starved) conditions, where this latest analysis now explicitly includes hydrogen pumping and emissions release when operating under oxygen-depleted conditions. In addition to considering diffusion effects and electrochemical effects, the model tracks the evolution of hydrogen in the cell cathode when no oxygen remains to generate water. The voltage response of the model under normal (non-starved) conditions is first validated for steady-state and transient (current step-change) conditions against previously published experiments, and then the model is used to simulate the cell voltage and stack hydrogen emissions behavior measured from three different commercially available fuel cell stacks. In the first fuel cell stack, a 9-cell commercial short stack, only one cell was fully oxygen-starved. Excellent agreement is seen between the measured and simulated hydrogen release concentrations (where air injection was used downstream of the stack to ensure adequate oxygen levels for measurement with a catalytic hydrogen sensor and to condense water vapor in the exhaust), where the role of hydrogen pumping is seen to contribute significantly to the release behavior. The first fuel cell stack is then used transiently in comparison with testing performed where the hydrogen injection level in the cell is changed quickly, where the model gives good agreement with the measured emission response and cell voltage behavior. Further comparisons with test data from a second and third 10-cell commercial short stack models operated with stack inlet hydrogen injection show good agreement with measured emissions onset versus current, where the observed threshold of starvation and emissions occurs a few percent sooner in the third model than the simulation, but the overall behavior is well predicted.

Simulation and performance analysis of Multiple PCS sensors system

In this paper, a novel circuit is presented which overcome a serious limitation found in case of multiple sensors system. In this novel system design only one reference electrode and few active components used that makes the implementation of a low-cost system for the supervision of water quality. Photo Catalytic Sensor (PCS) estimates the parameter BOD (Biological Oxygen Demand) which is generally used to estimate quality of water. The system proposed in this paper involves a balanced bridge approach using few electronic components that provides a correlation in the input-output signals of low-cost sensors. The main reason of employing a readout circuit to PCS circuitry, is the fact that the fluctuation of O2 influences the threshold voltage, which is internal parameter of the FET and can manifest itself as a voltage signal at output but as a function of the trans conductance gain. The trans-conductance is a passive parameter and in order to derive voltage or current signal from its fluctuations the sensor has to be attached to readout circuit. This circuit provides high sensitivity to the changes in percentage of O2 in the solution.