Catalytic Sensor Research Articles

An Ultrasensitive Light-up Cu(2+) Biosensor Using a New DNAzyme Cleaving a Phosphorothioate-Modified Substrate.

Cu(2+) is a very important metal ion in biology, environmental science, and industry. Developing biosensors for Cu(2+) is a key topic in analytical chemistry. DNAzyme-based sensors are highly attractive for their excellent sensitivity, stability, and programmability. In the past decade, a few Cu(2+) biosensors were reported using DNAzymes with DNA cleavage or DNA ligation activity. However, they require unstable ascorbate or imidazole activation. So far, no RNA-cleaving DNAzymes specific for Cu(2+) are known. In this work, a phosphorothioate (PS) RNA-containing library was used for in vitro selection, and a few new Cu(2+)-specific RNA-cleaving DNAzymes were isolated. Among them, a DNAzyme named PSCu10 was studied further. It has only eight nucleotides in the enzyme loop with a cleavage rate of 0.1 min(-1) in the presence of 1 μM Cu(2+) at pH 6.0 (its optimal pH). Between the two diastereomers of the PS RNA chiral center, the R(p) isomer is 37 times more active than the S(p) one. Among the other divalent metal ions, only Hg(2+) can cleave the substrate due to its extremely high thiophilicity. A catalytic beacon sensor was designed with a detection limit of 1.6 nM Cu(2+) and extremely high selectivity. PSCu10 is specific for Cu(2+), and it has no cleavage in the presence of ascorbate, which reduces Cu(2+) to Cu(+).

Micro catalytic methane sensors based on 3D quartz structures with cone-shaped cavities etched by high-resolution abrasive sand blasting

A novel quartz based micro catalytic methane sensor with back-etched cone-shaped cavity was fabricated by high-resolution abrasive sand blasting technique. Highly uniform micro cavities were easily and quickly achieved with a depth of 450μm and a bottom diameter of 600μm on a quartz substrate 500μm thick, followed by screen printing porous alumina with a position accuracy of 10μm and inkjet printing of co-metal catalyst with loading quantity resolution of 4.75ng. Compared with a bulk quartz substrate sensor, performance of the sensor fabricated by abrasive sand blasting is greatly improved with a lower thermal mass. The sensor’s temperature distribution profile is more concentrated on target catalyst, power consumption decreases to 285mW by 23%, thermal response time decreases to 8.8s by 79%, and sensitivity to methane increases to 1.83mV/% CH4 by 35%, with a high correlation coefficient up to 0.9986. Moreover, this sensor demonstrates excellent resistance to mechanical shock at high working temperatures, significantly superior to conventional silicon based membrane sensors. This design of the high performance sensor, together with the simple and fast MEMS-compatible fabrication process enables such catalytic sensors for mass production and combustible gas detecting in harsh environmental applications.

Hydrogen emission characterization for proton exchange membrane fuel cell during oxygen starvation – Part 1: Low oxygen concentration

Hydrogen emissions during low oxygen concentration appear in the cathode exhaust of a PEM fuel cell stack. In this paper, the hydrogen emission rates for a stack containing cells without hydrogen crossover leaks are characterized. A Ballard 9-cell Mk1100 stack under standard FCvelocity®1-HD6 bus module operating conditions is employed, and extensive experiments are conducted under current demand to evaluate individual cell voltages and quantify hydrogen emissions. The results indicate that the emission rates are a strong function of current demands.In parallel, a model is developed to estimate the amount of hydrogen in the cathode outlet. To illustrate the accuracy of the developed model, the simulation results and the measured hydrogen emission rates in the cathode exhaust are compared for two current demands. It is acknowledged that the proposed model can be a reliable emulator for the hydrogen sensor in the cathode exhaust, where catalytic sensors cannot perform correctly because of the lack of proper oxygen concentrations, or other types of sensor may fail due to wetting or sensor degradation. Moreover, the proposed model provides a user-friendly tool for systems engineers to design reliable start-up procedures for the control of hydrogen emissions.

Vision of new olfactory sensing array

A newly synthesized material with highly controllable, but partial selectivity is proposed for the construction of catalytic sensors comprising an olfactory array. The transduction principle proposed for this array is that of a fuel‐cell‐type amperometric sensor. In the example discussed here, it is based on electrochemical oxidation of lower aliphatic alcohols in an alkaline medium. Since a cyclic voltammogram of each sensor in the olfactory array provides high‐dimesional data, a pattern recognition technique including mutidimensional data generation, feature extraction, and classification is indispensable. The combination of the new sensor array with a sophisticated pattern recognition algorithm might lead to the next generation of olfactory sensing array. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A quartz-based micro catalytic methane sensor by high resolution screen printing

A micro catalytic methane sensor was proposed and fabricated on a bulk fused quartz substrate using a high resolution screen printing technique for the first time, with reduced power consumption and optimized sensitivity. The sensor was designed by the finite element method and quartz was chosen as the substrate material and alumina support with optimized dimensions. Fabrication of the sensor consisted of two MEMS processes, lift-off and high resolution screen printing, with the advantages of high yield and uniformity. When the sensor’s regional working temperature changes from 250 °C to 470 °C, its sensitivity increases, as well as the power consumption. The highest sensitivity can reach 1.52 mV/% CH4. A temperature of 300 °C was chosen as the optimized working temperature, and the sensor’s sensitivity, power consumption, nonlinearity and response time are 0.77 mV/% CH4, 415 mW, 2.6%, and 35 s, respectively. This simple, but highly uniform fabrication process and the reliable performance of this sensor may lead to wide applications for methane detection.

Nano-array integrated monolithic devices: toward rational materials design and multi-functional performance by scalable nanostructures assembly

The scalable three-dimensional (3-D) integration of functional nanostructures into applicable platforms represents a promising technology for meeting the ever-increasing demands of fabricating high performance devices featuring cost-effectiveness, structural sophistication and multi-functional enabling. Such an integration process generally involves a diverse array of nanostructural entities (nano-entities) consisting of dissimilar nanoscale building blocks such as nanoparticles, nanowires, and nanofilms made of metals, ceramics, or polymers. Various synthetic strategies and integration methods have enabled the successful assembly of both structurally and functionally tailored nano-arrays into a unique class of monolithic devices. The performance of nano-array based monolithic devices is dictated by a few important factors such as materials substrate selection, nanostructure composition and nano-architecture geometry. Therefore, the rational material selection and nano-entity manipulation during the nano-array integration process, aiming to exploit the advantageous characteristics of nanostructures and their ensembles, are critical steps towards bridging the design of nanostructure integrated monolithic devices with various practical applications. In this article, we highlight the latest research progress of the two-dimensional (2-D) and 3-D metal and metal oxide-based nanostructural integrations into prototype devices applicable with ultrahigh efficiency, good robustness and improved functionality. Select examples of nano-array integration, scalable nanomanufacturing and representative monolithic devices such as catalytic converters, sensors and batteries will be utilized as the connecting dots to display a roadmap from hierarchical nanostructural assembly to practical nanotechnology implications ranging from energy, environmental, to chemical and biotechnology areas.

Amino versus imino-transition metallic complexes in functionalized mesoporous silica: a lone pair degenerated into a singlet electron system

Imine terminated mesoporous silica nanoparticles (IMSNP) appear to be an effective mesoporous media with potential for multifarious applications such as catalytic support, effluent treatment, and sensors.

高速応答型水素センサの水素拡散追従性評価

Fast response and high durability hydrogen sensor is required in the safety management of hydrogen station and fuel cell vehicle. We had developed the catalytic combustion type hydrogen sensor in the shape of the miniature beads. We compared this fast response sensor with the conventional sensor in the performance of hydrogen leakage real-time monitoring. It was observed that the fast response sensor's output fluctuated with hydrogen concentration's short time change. It was confirmed that this fluctuation was useful for the early detection of the hydrogen leakage.

Assessment of Explosion Risks in the Presence of Hydrocarbon Mixtures

The most of gas associated industries face with the risks of explosion and fire which may lead to dire consequences. We present an approach for assessing the explosion risks in the presence of hydrocarbon mixtures when the chemical composition and concentration of gases in the mixture are unknown. The core idea is the measurement of warm dissipated during the combustion of hydrocarbons in the reaction chamber of the sensor. To evaluate this approach we use a catalytic planar sensor with limited gas diaphragm in the reaction chamber. We demonstrate the feasibility of our approach experimentally.

Platinum Nanoparticle Loading of Boron Nitride Aerogel and Its Use as a Novel Material for Low‐Power Catalytic Gas Sensing

A high‐surface‐area, highly crystalline boron nitride aerogel synthesized with nonhazardous reactants has been loaded with crystalline platinum nanoparticles to form a novel nanomaterial that exhibits many advantages for use in a catalytic gas sensing application. The platinum nanoparticle‐loaded boron nitride aerogel integrated onto a microheater platform allows for calorimetric propane detection. The boron nitride aerogel exhibits thermal stability up to 900 °C and supports disperse platinum nanoparticles, with no sintering observed after 24 h of high‐temperature testing. The high thermal conductivity and low density of the boron nitride aerogel result in an order of magnitude faster response and recovery times (<2 s) than reported on alumina support and allow for 10% duty cycling of the microheater with no loss in sensitivity. The resulting 1.5 mW sensor power consumption is two orders of magnitude less than commercially available catalytic gas sensors and unlocks the potential for wireless, battery‐powered catalytic gas sensing.

Методы повышения точности уреазной дыхательной диагностики helicobacter pylori

This article describes existing methods of H. pylori diseases diagnosis, procedures of interpreting acquired results and the diagnosis method with the use of semi-conductor catalytic gas sensors combined into the system.
 
 Gas sensors have cross-sensitivity to various gases in addition for which they are designed. The use of several sensors allows to reduce the influence of mixed gases. This method is especially useful within medical entities, where air inside can contain alcohol or chloramine vapors. Sensors are selected in the way to overlap main sensor´s cross-sensitivity zone to the maximum extent possible. This is how mixed gases´ influence on the main sensor is compensated. The proposed system uses methods of artificial neural network technology, which allows to enhance system´s stability in changing gas mixture. Due to microcontroller driven calculations, the system can automatically provide data processing. The proposed system can reduce the influence of factors that contribute uncertainty to the measurement result. These results can be transmitted to PC, which one can use to create electronic database or to hold case history.

Selected properties of Pt(111) modified surfaces: A DFT study

Abstract Density functional theory calculations were employed to investigate the electronic properties of a Pt(111) surface modified with foreign atoms. The effects of alloying platinum with molybdenum, palladium, and tin changed the interaction between adsorbate orbital and metal d band. This letter discusses the interaction between metal atoms and adsorbate and its influence on electronic structure rearrangement of the species—changes that must be taken into account to explain the behavior of catalytic systems and sensors. Mo/Pt(111) and Sn/Pt(111) exhibited lower susceptibility to poisoning by CO, compared with pure platinum. Both Pt-based materials are expected to find utility in electrodes for alcohol and hydrogen oxidation.

Improving interoperability of catalytic sensors

A huge number of combustible gas leaks occur every year at industrial and home facilities. These leaks may have grave consequences for health, environment and property. In this work we demonstrate the approach for improving the interoperability of catalytic sensors which are widely used in industrial monitoring applications for combustible gas leaks. To ensure methane detection within the broad concentration range (100ppm–100% vol.), we propose using of two sensors with catalysts in the modified Wheatstone sensing circuit and to cover them with sealed caps with different holes to enable gas diffusion control.

Adsorption/combustion-type VOC sensors employing mesoporous γ-alumina co-loaded with noble-metal and oxide

Mesoporous (mp-)Al2O3 powders, which were prepared by microwave-assisted solvothermal treatment of aluminum secondary butoxide in 1-propanol at 110°C followed by firing at 700°C in air, were loaded with l wt% MO (CeO2, CuO, Fe2O3, Mn2O3, NiO or RuO2, l≤20 (wt%)) by impregnation with the constituent metal salt in the aqueous solution followed by firing at 700°C in air. Thereafter the mp-Al2O3 powders loaded with and without MO were further co-loaded with noble metal nanoparticles, which were synthesized by sonochemical reduction. The VOC-sensing properties of the adsorption/combustion-type gas sensors fabricated by MEMS technology and drop coating technique utilizing the mN1/nN2/mp-Al2O3, 1.0Pt/mp-Al2O3 and 1.0Pt/lMO/mp-Al2O3 (N1, N2: Au, Pd and Pt, m and n: the amount of N1 and N2 nanoparticles loaded, m+n=1.0 (wt%)) obtained as sensor materials were investigated in this study. The general ethanol response (ΔVMAX) of all mAu/nPt/mp-Al2O3 sensors was smaller than that of the 0.2Au/0.8Pd/mp-Al2O3 sensor, which showed the largest ΔVMAX among mAu/nPd/mp-Al2O3 sensors in our previous study. In the series of mPt/nPd/mp-Al2O3 sensors, on the other hand, the 0.8Pt/0.2Pd/mp-Al2O3 sensor showed larger ΔVMAX to ethanol than that of the 0.2Au/0.8Pd/mp-Al2O3 sensor. Moreover, the ΔVMAX of the Pt/mp-Al2O3 sensor to ethanol was slightly larger than of the 0.8Pt/0.2Pd/mp-Al2O3 sensor. The co-loading of 10wt% MO with 1.0wt% Pt nanoparticles onto the mp-Al2O3 was effective in improving the ΔVMAX to ethanol of the Pt/mp-Al2O3 sensor in some cases, and the 1.0Pt/10CeO2/mp-Al2O3 sensor showed the largest ΔVMAX to ethanol among all the 1.0Pt/10MO/mp-Al2O3 sensors tested. The ΔVMAX of the 1.0Pt/10CeO2/mp-Al2O3 sensor to other VOCs (acetone, ethyl acetate, benzene, toluene and o-xylene) was relatively smaller than that to ethanol, but the shape of the differential sensor-signal profiles largely depended on the kind of VOCs and thus detailed analyses by the differential processing may have an advantage in the VOC-selective detection. On the other hand, integral processing of the sensor-signal profiles showed that the magnitude of the approximately integrated dynamic response (IDR), which was largely dependent on the amount of VOCs adsorbed on the mp-Al2O3, may provide an indication of the quantitative VOC detection. Furthermore, the control of the amount of CeO2 loaded and the value of low temperature at pulse-driven heating enabled the 1.0Pt/lCeO2/mp-Al2O3 sensors to detect a small amount of VOCs in comparison with general catalytic combustion-type gas sensors, because of the large IDR to the VOCs at a low-concentration range.

Artificial enzyme-based catalytic sensor for the electrochemical detection of 5-hydroxyindole-3-acetic acid tumor marker in urine

A novel approach towards the development of biomimetic electrochemical sensors is presented. It is based on magnetic-core/porous-shell molecularly imprinted composites as recognition phase. The selected substrate is 5-hydroxyindole-3-acetic acid (5-HIAA), an urinary metabolite used as carcinoid tumor maker. Using 5-HIAA as template molecule, hemin, 4-vinylpyridine and ethylenglycoldimethacrylate crosslinker are polymerized onto the magnetic core to obtain an artificial enzyme with peroxidase activity. An aliquot of a suspension of the resulting material is deposited onto a carbon screen printed electrode, and the solid material is fixed with a permanent magnet to prepare the sensor. The product of the catalytic oxidation of 5-HIAA at the sensing phase is monitored by differential pulse voltammetry. This sensor allows the detection of 5-HIAA with good sensitivity (0.72±0.01nAμM−1) and linear response over a concentration range covering the whole window of normal and pathologic urinary levels of 5-HIAA 1–50μM (0.2–9.6ppm) with a detection limit of 1.4μM (0.27ppm). Urine samples of healthy individuals, spiked with known concentrations of 5-HIAA, yield good recovery values and reproducibility for normal and pathological concentrations (90–100% recovery values, with RSD below 10%).

In vitro selection of a sodium-specific DNAzyme and its application in intracellular sensing

Over the past two decades, enormous progress has been made in designing fluorescent sensors or probes for divalent metal ions. In contrast, the development of fluorescent sensors for monovalent metal ions, such as sodium (Na(+)), has remained underdeveloped, even though Na(+) is one the most abundant metal ions in biological systems and plays a critical role in many biological processes. Here, we report the in vitro selection of the first (to our knowledge) Na(+)-specific, RNA-cleaving deoxyribozyme (DNAzyme) with a fast catalytic rate [observed rate constant (ko(bs)) ∼ 0.1 min(-1)], and the transformation of this DNAzyme into a fluorescent sensor for Na(+) by labeling the enzyme strand with a quencher at the 3' end, and the DNA substrate strand with a fluorophore and a quencher at the 5' and 3' ends, respectively. The presence of Na(+) catalyzed cleavage of the substrate strand at an internal ribonucleotide adenosine (rA) site, resulting in release of the fluorophore from its quenchers and thus a significant increase in fluorescence signal. The sensor displays a remarkable selectivity (>10,000-fold) for Na(+) over competing metal ions and has a detection limit of 135 µM (3.1 ppm). Furthermore, we demonstrate that this DNAzyme-based sensor can readily enter cells with the aid of α-helical cationic polypeptides. Finally, by protecting the cleavage site of the Na(+)-specific DNAzyme with a photolabile o-nitrobenzyl group, we achieved controlled activation of the sensor after DNAzyme delivery into cells. Together, these results demonstrate that such a DNAzyme-based sensor provides a promising platform for detection and quantification of Na(+) in living cells.

Conducting shrinkable nanocomposite based on au-nanoparticle implanted plastic sheet: tunable thermally induced surface wrinkling.

A thermally shrinkable and conductive nanocomposite material is prepared by supersonic cluster beam implantation (SCBI) of neutral Au nanoparticles (Au NPs) into a commercially available thermo-retractable polystyrene (PS) sheet. Micronanowrinkling is obtained during shrinking, which is studied by means of SEM, TEM and AFM imaging. Characteristic periodicity is determined and correlated with nanoparticle implantation dose, which permits us to tune the topographic pattern. Remarkable differences emerged with respect to the well-known case of wrinkling of bilayer metal-polymer. Wrinkled composite surfaces are characterized by a peculiar multiscale structuring that promises potential technological applications in the field of catalytic surfaces, sensors, biointerfaces, and optics, among others.

Sensor transition failure in the high flow sampler: Implications for methane emission inventories of natural gas infrastructure

Quantification of leaks from natural gas (NG) infrastructure is a key step in reducing emissions of the greenhouse gas methane (CH4), particularly as NG becomes a larger component of domestic energy supply. The U.S. Environmental Protection Agency (EPA) requires measurement and reporting of emissions of CH4 from NG transmission, storage, and processing facilities, and the high-flow sampler (or high-volume sampler) is one of the tools approved for this by the EPA. The Bacharach Hi-Flow Sampler (BHFS) is the only commercially available high-flow instrument, and it is also used throughout the NG supply chain for directed inspection and maintenance, emission factor development, and greenhouse gas reduction programs. Here we document failure of the BHFS to transition from a catalytic oxidation sensor used to measure low NG (~5% or less) concentrations to a thermal conductivity sensor for higher concentrations (from ~5% to 100%), resulting in underestimation of NG emission rates. Our analysis includes both our own field testing and analysis of data from two other studies (Modrak et al., 2012; City of Fort Worth, 2011). Although this failure is not completely understood, and although we do not know if all BHFS models are similarly affected, sensor transition failure has been observed under one or more of these conditions: (1) Calibration is more than ~2 weeks old; (2) firmware is out of date; or (3) the composition of the NG source is less than ~91% CH4. The extent to which this issue has affected recent emission studies is uncertain, but the analysis presented here suggests that the problem could be widespread. Furthermore, it is critical that this problem be resolved before the onset of regulations on CH4 emissions from the oil and gas industry, as the BHFS is a popular instrument for these measurements.Implications: An instrument commonly used to measure leaks in natural gas infrastructure has a critical sensor transition failure issue that results in underestimation of leaks, with implications for greenhouse gas emissions estimates as well as safety.

Selectivity and resistance to poisons of commercial hydrogen sensors

The resistance of several models of catalytic, workfunction-based metal-oxide-semiconductor and electrochemical hydrogen sensors to chemical contaminants such as SO2, H2S, NO2 and hexamethyldisiloxane (HMDS) has been investigated. These sensor platforms are among the most commonly used for the detection of hydrogen. The evaluation protocols were based on the methods recommended in the ISO 26142:2010 standard. Permanent alteration of the sensor response to the target analyte (H2) following exposure to potential poisons at the concentrations specified in ISO 26142 was rarely observed. Although a shift in the baseline response was often observed during exposure to the potential poisons, only in a few cases did this shift persist after removal of the contaminants. Overall, the resistance of the sensors to poisoning was good. However, a change in sensitivity to hydrogen was observed in the electrochemical platform after exposure to NO2 and for a catalytic sensor during exposure to SO2. The siloxane resistance test prescribed in ISO 26142, based on exposure to 10 ppm HMDS, may possibly not properly reflect sensor robustness to siloxanes. Further evaluation of the resistance of sensors to other Si-based contaminants and other exposure profiles (e.g., concentration, exposure times) is needed.

Novel FGMOS based PCS device for low power applications

The spice model for photo catalytic sensor (PCS) proposed by Whig and Ahmad overcomes several drawbacks like complex designing, non-linearity, and long computation time generally found in the flow injection analysis (FIA) technique by Yoon-Chang Kim et al. for the determination of chemical oxygen demand (COD). The FIA technique involves the complete analysis including sampling and washing. The flow injection analysis is an analytical method for the measurement of the chemical oxygen demand by using the photochemical column. This method uses a bulky setup and takes 10 minutes to 15 minutes to get the output result which is a tedious and time consuming job. If the conventional method is continuously used for a long time then it is stable only for 15 days. The purpose of this paper is to propose a new floating gate photo catalytic sensor (FGPCS) approach which has low power consumption and more user-friendly, and it is fast in operation by the modeling and optimization of sensor used for water quality monitoring. The proposed model operates under sub-threshold conditions which are appreciated in large integrated system design. The results of simulation are found to be fairly in agreement with the theoretical predictions. The results exhibit near linear variations of parameters of interest with appreciably reduced response time.