Ionic liquid high temperature gas sensors

An ionic liquid piezoelectric gas sensor was demonstrated for detection of polar and nonpolar organic vapors at high temperature with fast linear and reversible response.     

Miniature pressure sensors and their temperature compensation

A signal-conditioning IC was designed for a family of miniature pressure sensors. It converts the small output signal of the strain gauge bridges to a single-ended and amplified signal. In addition, it provides the possibility of laser trimming to align each individual specimen in the course of production. Furthermore, all linear temperature drifts over a wide range of temperatures are compensated by the temperature-dependent thin films.     

Advances in materials for room temperature hydrogen sensors

Hydrogen (H(2)), as a source of energy, continues to be a compelling choice in applications ranging from fuel cells and propulsion systems to feedstock for chemical, metallurgical and other industrial processes. H(2), being a clean, reliable, and affordable source, is finding ever increasing use in distributed electric power generation and H(2) fuelled cars. Although still under 0.1%, the distributed use of H(2) is the fastest growing area. In distributed H(2) storage, distribution, and consumption, safety continues to be a critical aspect. Affordable safety systems for distributed H(2) applications are critical for the H(2) economy to take hold. Advances in H(2) sensors are driven by specificity, reliability, repeatability, stability, cost, size, response time, recovery time, operating temperature, humidity range, and power consumption. Ambient temperature sensors for H(2) detection are increasingly being explored as they offer specificity, stability and robustness of high temperature sensors with lower operational costs and significantly longer operational lifetimes. This review summarizes and highlights recent developments in room temperature H(2) sensors.     

Polyantimonic acid-based materials evaluated as moisture sensors at ambient temperature

Humidity sensors are in high demand for many applications, such as environmental monitoring and air and food quality control. Despite many inorganic and organic materials exhibit moisture sensing properties, the electrical response of many existing sensors is not stable along the time. Polyantimonic acid (PAA) is characterized by elevated proton conductivity and by high thermal stability: consequently, it is seen as promising proton conductor for usage in humidity sensing devices. In this work, for the first time, PAA-based bulk solid membranes were produced and tested as potential materials for relative humidity (RH) detection and their moisture sensitivity was evaluated. Two different amounts of binder were used for moulding the solid sensors: the ones with 10% of binder were designated as 90PAA, while the ones with 20% were named 80PAA. The structures of the solid samples were investigated by X-ray diffraction (XRD) technique, adsorption–desorption curves via Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) techniques. The electrical behaviour was examined at ambient temperature by electrical impedance spectroscopy in the entire relative humidity (RH) interval (0–100%) and in the frequency range of 40 Hz up to 60 MHz. Electrical response of the materials was correlated with the structural features of the membranes. Both 90PAA and 80PAA sensors showed total resistance 3 × 10⁵ and 3.5 × 10⁵ Ω at 10% RH, respectively. A linear decrease of the resistance on RH was observed in the range 30–90% RH for both sensors. The electrical response of the evaluated PAA-based sensors displays good repeatability and reproducibility: the ones with lower binder content showed higher moisture sensitivity as well as very good time stability over 1 year.

     

Micro flow sensor based on two closely spaced amperometric sensors

In this communication, a novel micro flow sensor based on two closely spaced amperometric oxygen sensors is proposed and implemented. The simulation results show that the ratio of the responses of these two oxygen sensors is determined by flow rates in the micro-channel. The sensor has been implemented using a micro fabrication technique. The measurement results demonstrate that the technique is able to detect flow rates in the flow range of several microliters per minute when the distance between the working electrodes of two oxygen sensors is 10 microm and the cross-section of the micro-channel is 100 microm x 100 microm. The advantage of the proposed flow sensor is that no additional tracers have to be added or produced during the flow measurement. Information on dissolved oxygen concentration in the liquid is not required either.     

Fluorescent photoionic devices with two receptors and two switching mechanisms: applications to pH sensors and implications for metal ion detection

Two leading designs of fluorescent sensors are combined to yield the novel hybrid system of the ‘Fluorophore-Receptor₁-Spacer-Receptor₂’ format. We use 4-(dialkylaminoalkylamino)-7-nitrobenzo-2-oxa-1,3-diazoles as examples. The emission from internal charge transfer excited states in the present instances are highly responsive to N-H deprotonation as well as being quenched by intramolecular tertiary amine groups via photoinduced electron transfer (PET). When applied to pH sensing, this leads in favourable cases to two steps in the fluorescence-pH profile which can be viewed as a multi-stable photoionic device, even though single steps are more usual. The former situation is favoured when the two proton-associated equilibria are sufficiently separated on the pH scale and when the PET process is of moderate efficiency. These systems have the added feature of excitation/emission wavelengths in the visible region. As a secondary theme, we point out that caution is required when designing sensors for transition metal ions from systems with intrinsically proton-sensitive fluorescence due to receptors either integrated with or spaced from the fluorophore.     

Analytical chemistry with optical sensors

Summary Recent advances in opto-electronics, (fiber) optics, and optical spectroscopy have led to the development of a fascinating new chemical sensor technique. The present state of the art in optical sensing technology is briefly described in this review. Major advantages of this type of sensor over others include cheapness, ease of miniaturization and the renunciation of reference cells. Among the disadvantages, mention should be made of interference by ambient light, comparatively small analytical ranges, lack of specificity and lack of low-priced lasers.Potential fields of application include environmental control, process control (as, for instance, in chemical plants and bioreactors), remote sensing via long optical fibers or even from aircraft or satellites, and biomedical applications. Representative sensor types are described in some detail and potential future trends are discussed.

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Analytische Chemie mit Hilfe optischer Sensoren

Zusammenfassung Fortschritte auf dem Gebiet der Opto-Elektronik, (Faser)optik, und optischen Spektroskopie haben zur Entwicklung einer faszinierenden neuen Technik für chemische Sensoren geführt. In diesem Artikel wird der gegenwärtige Stand auf dem Gebiet der optischen Sensortechnologie beschrieben. Die Hauptvorteile dieses Sensortyps gegenüber anderen liegt in den günstigen Kosten, der leichten Miniaturisierbarkeit, und dem Verzicht auf eine Referenz-Zelle. Von den Nachteilen sind zu erwähnen die Störungen durch Umgebungslicht, vergleichsweise kleine analytische Bereiche, geringe Spezifität, und der Mangel an billigen Laserlichtquellen.Potentielle Anwendungsgebiete sind die Umweltkontrolle, Prozeßkontrolle (etwa in chemischen Fabriken oder Bioreaktoren), die Verfolgung von analytischen Parametern über große Entfernungen, etwa mit Hilfe von langen Lichtleitern oder sogar von Flugzeugen oder Satelliten, und biomedizinische Anwendungen. Einige repräsentative Sensortypen werden etwas genauer beschrieben und potentielle Zukunftsentwicklungen diskutiert.

     

The thermodynamic viability of yttria-stabilized zirconia pH sensors for high temperature aqueous solutions

The thermodynamic viability of the yttria-stabilized zirconia sensor (YSZS) [H₂O, H⁺/ZrO₂(Y₂O₃)/HgO/Hg] for the measurement of pH in high temperature aqueous solutions is evaluated by measuring potentials for this electrode and a conventional hydrogen electrode (HE) against a common reference electrode in a variety of solutions [0.01m H₃PO₄, 1m Na₂SO₄, 0.01m B(OH)₃+0.01m KOH, and 0.01m KOH] at temperatures from 298.15K (25°C) to 573.115K (300°C). In order to compare theoretical and experimental potentials for the cell

Suspended microchannel resonators with piezoresistive sensors

Precision frequency detection has enabled the suspended microchannel resonator (SMR) to weigh single living cells, single nanoparticles, and adsorbed protein layers in fluid. To date, the SMR resonance frequency has been determined optically, which requires the use of an external laser and photodiode and cannot be easily arrayed for multiplexed measurements. Here we demonstrate the first electronic detection of SMR resonance frequency by fabricating piezoresistive sensors using ion implantation into single crystal silicon resonators. To validate the piezoresistive SMR, buoyant mass histograms of budding yeast cells and a mixture of 1.6, 2.0, 2.5, and 3.0 μm diameter polystyrene beads are measured. For SMRs designed to weigh micron-sized particles and cells, the mass resolution achieved with piezoresistive detection (～3.4 fg in a 1 kHz bandwidth) is comparable to what can be achieved by the conventional optical-lever detector. Eliminating the need for expensive and delicate optical components will enable new uses for the SMR in both multiplexed and field deployable applications.     

Chemical sensors with chalcogenide glassy membranes

The present review is emphasized on the recent achievements in the application of chalcogenide glasses (ChG) as membrane materials in chemical sensors, microsensors and multisensor systems. The questions concerning material synthesis, sensor designs and the concepts for the potential-generating mechanisms have briefly discussed. Most of the chalcogenide glass-forming systems and compositions investigated as membrane active materials have been summarized, and their analytical characteristics have been considered. The efficiency of chalcogenide-based chemical sensors in the real system analyses, as well as the advantages and disadvantages in their analytical performance have been evaluated and compared with the corresponding polycrystalline analogous.     

Selecting fruits with carbon nanotube sensors

Sensor strategy bears fruit: A nature-inspired Cu(I) complex was employed to fabricate single-walled carbon nanotube sensors that can selectively detect ethylene gas at concentrations as low as 0.5?ppm. Such nanosensors may be used to monitor ethylene gas emitted from fruits to monitor their ripening.     

Comparative study between two fabricated potentiometric sensors to enhance selectivity towards ferrous ions

Electroanalytical methods are highly selective for measuring electrical quantities including the charge, potential and current with their relation to chemical parameters. They are widely applied in various fields such as biochemical analysis, industrial quality control and environmental monitoring. They have many advantages over other techniques in that they are not time consuming and are specific for certain oxidation states of certain elements which give these techniques high selectivity and sensitivity features. This paper is based on two parts: the first part describes the fabrication of screen‐printed electrodes (SPEs) modified with methyl red as electroactive material, while second part describes the preparation and characterization of Fe(II)–methyl red complex using various spectroscopic tools, the complex being used for the construction of carbon paste electrodes (CPEs). The two proposed electrodes were successfully applied for the determination of Fe(II) in water and pharmaceutical (pharovit) samples. The electrodes under investigation show potentiometric response for Fe(II) in the concentration range 8.0 × 10^?7–1.0 × 10^?2 and 5.0 × 10^?7–1.0 × 10^?2 M at 25°C for SPE and CPE, respectively, and the electrode response is independent of pH in the range 1.5–7.0. These sensors show Nernstian slopes of 29.1 ± 0.2 and 29.7 ± 0.16 mV decade^?1 with detection limit values of 8.0 × 10^?7 and 5.0 × 10^?7 M for SPE and CPE, respectively. These electrodes show fast response time of 6 and 4 s and exhibit a lifetime of 100 and 30 days for SPE and CPE, respectively. The mechanism of chemical reaction between modifier and Fe(II) on the SPE surface was studied using infrared spectra, scanning electron microscopy and energy‐dispersive X‐ray analysis. The proposed potentiometric method was validated according to the IUPAC recommendations. The results obtained using the proposed sensors were comparable with those obtained with inductively coupled plasma analysis.     

Capacitive porous silicon sensors for measurement of low alcohol gas concentration at room temperature

Capacitive alcohol gas sensors using a porous silicon (PS) layer were fabricated and investigated for the measurement of breath alcohol concentration. Since the PS layer shows high adsorption against ethanol along with a large internal surface area, detecting low alcohol gas concentrations without any heating may be realized in comparison with metal oxide sensors. In this work, we measured the capacitance for the range of 0–0.5% alcohol concentrations using the proposed sensors, and observed how illumination of UV light affected the sensitivity. In addition, the effect of CO₂ and N₂ gases involved commonly in exhaling breath was estimated, and the same experiment for methanol gas was executed to compare qualitatively with ethanol gas. Received: 23 July 1999 / Accepted: 15 October 1999     

Mechanism of the interaction of CO2 and humidity with primary amino group systems for room temperature CO2 sensors

The use of primary amino groups as receptors to detect CO₂ is promising because of their ability to perform reversible acid-base-reactions. In contrast to other sensitive materials using this effect, evaluable signals can be obtained even at ambient temperature. The effect discussed for most of the previously used sensing layers is the formation of bicarbonate species, which needs H₂O as well as an increased temperature. The use of primary amino groups and work function readout appears to be dominated by another reaction, the reversible formation of carbamate, which does not require any water presence and, in addition to that, is more efficient at lower temperatures. To confirm this hypothesis, IR-, Raman-, XPS- and NMR-spectroscopy were used.     

Effects of anionic surfactant SDS on the photophysical properties of two fluorescent molecular sensors

Two fluorescent molecular sensors CS1 and CS2 were designed and synthesized to probe the aggregate behavior of anionic surfactant SDS. CS1 was based on the photo-induced electron transfer (PET) mechanism, while CS2 was founded on the intramolecular charge transfer (ICT) mechanism. The photophysical properties of CS1–2 in anionic surfactant sodium dodecyl sulfate (SDS) solution were studied by fluorescence and UV–vis methods. The experimental results show that significant absorption and emission spectral responses of CS1 were observed with the addition of SDS: the absorbance and fluorescence intensity decreased first and then increased. The plot of fluorescence intensity of CS1 versus SDS concentration showed two break points, which might be ascribed to the critical micellar concentration (cmc) and the formation of premicelle (cac) aggregate, respectively. But the solution’s color of CS2 changed from yellow to red with increasing SDS concentrations. The large red-shift in both absorption (50 nm) and emission (55 nm) spectra of CS2 was resulted from the protonation of the electron accepting moiety (NC nitrogen), which enhanced the “push–pull” interaction of the ICT fluorophore. This was facilitated by the increase of local H⁺ concentration around SDS premicelle and micelle. As a consequence, pK_a values of CS1 and CS2 were elevated in SDS micelle.     

Probing disaccharide selectivity with modular fluorescent sensors

Six modular photoinduced electron transfer (PET) sensors bearing two phenylboronic acid receptors have been evaluated as fluorescent disaccharide sensors. The length of linker separating the two boronic acid moieties was varied and the sensors’ interaction with disaccharides assessed via fluorescence spectroscopy. It was shown that saccharide selectivity was influenced by the choice of linker length. Diboronic acid sensors 3_n also displayed significant specificity for the disaccharides linked to the carbon on the 3rd or 6th position (as numbered from the anomeric centre) over those linked at the 4th position.     

Optimizing cross-reactivity with evolutionary search for sensors

We report a straightforward evolutionary procedure to build an optimal sensor array from a pool of DNA sequences oriented toward three-way junctions. The individual sensors were mined from this pool under separate selection pressures to interact with four steroids, while allowing cross-reactivity, in a manner designed to achieve perfect classification of individual steroids. The resulting sensor array had three sensors and displayed discriminatory capacity between steroid classes over full ranges of concentrations. We propose that similar protocols can be used whenever we have two or more classes of samples, with individual classes being defined through gross differences in ratios of dominant families of responsive components.     

Oxygen doping modulating thermal-activated charge transport of reduced graphene oxide for high performance temperature sensors

Graphene and its derivatives have sparked intense research interest in wearable temperature sensing due to their excellent electric properties, mechanical flexibility, and good biocompatibility. Despite these advantages, the weak temperature dependence of charge transport makes them difficult to achieve a highly sensitive temperature response, which is one of the remaining bottlenecks in the progress towards practical applications. Unfortunately, detailed knowledge about the key factors of the charge transport temperature dependence in this material that determines the critical performance of electrical sensors is very limited up to now. Here, we reveal that oxygen absorption on the ultrathin reduced graphene oxide (RGO) films (∼3 nm) can significantly increase their conductance activation energy over 200% and thus greatly improve the temperature dependence of thermal-activated charge transport. Further investigations suggest that oxygen introduces the deep acceptor states, distributed at an energy level ∼0.175 eV from the valence-band maximum, which allows a highly temperature-dependent impurity ionization process and the resulting vast holes release in a wide temperature range. Remarkably, our temperature sensors based on oxygen-doped ultrathin RGO films show a high sensitivity with temperature conductive coefficient of 14.58% K⁻¹, which is one order of magnitude higher than the reported CNT or graphene-based devices. Moreover, the ultrathin thickness and high thermal conductivity of RGO film allow an ultrafast response time of ∼86 ms, which represents the best level of temperature sensors based on soft materials. Profiting from these advantages, our sensors show good capacity to identify the slight temperature difference of human body, monitor respiratory rate, and detect the environmental temperature. This work not only represents substantial performance advances in temperature sensing, but also provides a new approach to modulate the charge transport temperature dependence, which could be benefited to both device design and fundamental research.     

Lipopolysaccharide identification with functionalized polydiacetylene liposome sensors

The outer membrane of Gram negative bacteria contains lipopolysaccharides, which are glycolipids with carbohydrate sequences that are unique for each bacterial species and serotype. In this communication, we report a method for identifying LPS from different bacteria using an electronic tongue approach. Two functionalized polydiacetylene liposomes were used as colorimetric sensors for detecting various types of LPS. These liposomes were assayed under four different experimental conditions to generate a data set of eight colorimetric responses. This data set constitutes a unique fingerprint for each analyte and permits identification of each LPS type.