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Background: The development of phantoms to reduce animal testing or to validate new instruments or operation techniques is of increasing importance. For this reason, a blood circulation phantom was developed to test a newly designed retractor system with an integrated oxygen sensor. This phantom was used to evaluate the impact of the 3D printed blood vessel on the measurement of the oxygen saturation. Methods: A solution of nickel sulfate and copper sulfate was prepared as a substitute for real blood. The absorption spectra of these solutions were recorded and compared with those of blood. Subsequently, the oxygen sensor used was calibrated to the blood substitute. Additionally, blood vessels with a simplified geometry were designed and manufactured using inverted vat polymerization and an elastic material (Formlabs Elastic 50 A). To determine the orientation during the printing process, various vessels were printed. Measurements to assess the effects of disturbance (rotation of the vessels during measurements) on the sensor readouts were prepared. Results: The impact of disturbances was verified through the rotation of the 3D printed vessels. It was demonstrated that a direct measurement on the disturbances led to outliers and higher values. An optimal orientation was determined to be a lateral placement (90° or 270°) of the sensor. Regarding the orientation of the vessels within the printing space, an orientation of 45° yielded the best results, as the individual layers had the least impact on the light emitted and received by the oxygen sensor. Conclusion: The achieved results demonstrate the influence of the orientation of the vessel during 3D printing as well as the influence of the position of the vessel during the measurement using a conventional oxygen sensor. [ABSTRACT FROM AUTHOR]

Ni–30Cr model alloy was used to study chromia-scale formation behaviour. During its formation the mass variation signal is weak and it is important to take specific care to measure oxidation kinetics by thermogravimetric analysis. Symmetrical design allows the determination of very small mass changes in compensating buoyancy effects and limiting measurement drift. The mass variation measurement comprises noise coming from different sources that affects the electronic signal. It must be minimised to improve accuracy. This involves keeping the room-temperature constant, strictly balancing the beam and minimising buoyancy effects. By this way it was possible to acquire kinetics and to measured rate constants, kp, in a range from 3.10–5 to 3.10–10 mg2.cm−4.s−1 equivalent to 10–12 down to 10–17 cm2.s−1. Oxygen partial pressure ( P O 2 ) was monitor and revealed an abnormal consumption of oxygen at the beginning of the thermal exposure. Experiments with an inert material showed parasitic reactions identified by mass spectrometry as combustion of impurities. As oxygen consumption is not only due to oxidation of the sample, corrosion kinetics can't be deduced from it. Hence, to determine whether the oxygen supply from the gas is a limiting parameter, a model, which quantifies oxygen consumption by sample oxidation within the thermobalance, is proposed. [ABSTRACT FROM AUTHOR]

Bare, non-pretreated platinum wires and screen-printed platinum electrodes were used as both working and counter electrodes in the measurement of dissolved oxygen using a chronoamperometric method. The oxygen reduction current response in the diffusion state was used for a linear determination of air saturation. We evaluated the two different materials in general for their sensing performance such as conditioning time, accuracy, resolution and stability over 13 h of continuous mid-term measurement. A good performance was found for the wire electrodes in terms of accuracy with a current slope of 1.0–1.6 µA (% as)-1 and a resolution of 10–15 nA (Lowest Level of Detection = 0.1% as), but with an unstable current response result over the course of the measurement. The screen-printed electrodes have a resolution of 10–18 nA (Lowest Level of Detection = 0.6–0.8% as) and an accuracy of 620–660 nA (% as)-1 but they showed promising reproducibility and stability. Both materials require several hours of conditioning in the chronoamperometric method before a stable current response is achieved. For biotechnological applications, the platinum screen printed electrodes were evaluated in typical parameter settings (pH 4.0 and 7.4, salinity 0.1 to 10x phosphate buffered saline and temperature 12 to 42 °C) and showed correlations between the response time and stability and the temperature. No correlations were found between salinity, pH and the current response. In this paper, we present inexpensive electrode materials and a simple to implement chronoamperometric method for reliable direct measurement of dissolved oxygen in aqueous media. [ABSTRACT FROM AUTHOR]

Intelligent food packaging with the multisensory analysis is promising as the next generation technology of food packaging. The oxygen content in food packaging is one of the crucial parameters affecting the food quality and shelf life. Caviar is among the most nutritious and costly food sources. Here, a photonic oxygen-sensing system, based on the time-resolved phosphorescence spectroscopy of a platinum complex, is developed for non-contact, non-intrusive, and real-time vacuum packaging quality control, and implemented for caviar packaging. The sensor is embedded in protective polyethylene layers and excited with a short-pulsed light emitting diode (LED) source. Integration of a blue pulsed light source, a fast and amplified silicon photodiode controlled by the Spartan-6 field programmable gate array (FPGA), and a long lifetime platinum complex results in a photonics-based oxygen sensor with a fast response and high sensitivity to the vacuum packaging damage, which is suitable for caviar. It is revealed that applying the polyethylene layers protects the caviar from the platinum complex, leaching while not interfering with the sensor functionality. Characterizing the photonic system based on its sensitivity, repeatability, stability, and long-term operation demonstrates its capability for this application. [ABSTRACT FROM AUTHOR]

(8YSZ)1−x(Cr2O3)x (x = 0, 0.05, 0.10, 0.15) are prepared by the co-precipitation method. Diffraction peaks of the samples belonged to the cubic fluorite structure. Conductivity decreases first and then increases with increasing Cr2O3 content. An oxygen sensor based on 8YSZ solid electrolyte and (8YSZ)0.85(Cr2O3)0.15 diffusion barrier is prepared by the Pt slurry bonding method. The sensor has a limiting current plateau at 2% oxygen concentrations within 720 ~ 870 °C. The oxygen sensor has a linear relationship between the log IL and 1000/T. At 850 °C, a linear relationship between the limiting current IL and oxygen concentration x(O2) is established for the oxygen sensor. The oxygen sensor is provided with a limiting current plateau within the experimental concentration division, and the limiting current plateau is not affected by x(CO2) and p(H2O). I-V curves of the oxygen sensor overlap, and the limiting current plateaus are almost equal under the long-term high-temperature operating conditions of 144 h. [ABSTRACT FROM AUTHOR]

An oxygen pump sensor was installed in front of an oxidation furnace to supply and discharge oxygen to the Ar–H2O atmosphere and accurately control the oxygen partial pressure in the atmosphere. Furthermore, the oxidation rate was set after the oxidation furnace. It was measured by an oxygen sensor and a hydrogen sensor. Pure iron was used as the sample. The purpose of this study was to clarify the oxidation behavior of water vapor and oxygen. As a result, it was clarified that the amount of hydrogen generated by the oxidation of water vapor and Fe decreases when oxygen is supplied. In addition, when the oxygen supply amount increased, oxidation by the water vapor did not occur. On the other hand, it was clarified that when oxygen in the atmosphere is discharged, oxidation by oxygen is suppressed and only oxidation by the water vapor occurs. In the cross-sectional microstructure after oxidation, Fe3O4 was formed in the outer layer in the environment where the oxygen was discharged, but by supplying oxygen, the oxide layer became thicker and Fe2O3 was formed in the outer layer. The mass gain increased as the oxygen was supplied. Considering the ratio of oxidation by water vapor and oxidation by oxygen, it was clarified by this method that the mass gain is greater when the oxidation by oxygen is dominant. [ABSTRACT FROM AUTHOR]

The motorcycles are unignorable near-ground pollutant emission sources that increase the human exposure in the dense area. However, the information of the polycyclic aromatic hydrocarbons (PAHs) emissions under different scenarios of engine and emission control for motorcycle is limited. This study focused on the PAH emissions from two fuel-injection types of motorcycles, including the premixed fuel-injection (PFi) with carburetor and electronic fuel-injection (EFi). Specifically, the effects of throttle opening (TO), secondary air system (SAS), oxygen sensor (OS), oxidation catalytic converter (OCC), and three-way catalytic converter (TWC) on PAH emissions are investigated. Results show that the PAH emission concentrations increase 227–727%, 351–492%, and 155–408% by the increasing TO ratio, unworking SAS, and OS units in both motorcycles. For the PFi engine, the OCC unit is found to be more effective in PAH control (31–89%) than the SAS system (72–80%), especially under low TO operation. For the EFi engine which dominates the motorcycle market recently, the oxygen sensor for more accurate combustion control shows a better PAH reduction (36–76%) than TWC system (21–66%). The ultra-fine particulate phase PAHs, which is hardly removed by catalyst, needs to be further considered. Moreover, the total PAH emission level of the EFi engine is still about ten times higher than that of the PFi. By the annual emission calculation for three densely populated countries, the recent evolution significantly reduces the annual hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) emissions but have unignorable PAH emissions. These emissions continuously affect the human health in the near-ground urban air and need to be considered in the next generation of motorcycle design. [ABSTRACT FROM AUTHOR]

The lithium niobate used in an ultrasonic transducer for liquid metal fast nuclear reactors is prone to a reduction leading to a rapid short circuit of the sensor in operating conditions. Oxygen consumption on stainless steel sensor's walls was suspected to be the cause of the reduction. Impedance spectroscopy monitoring around 600 °C under different O2 partial pressures shows that the reduction limit is above the equilibrium pressure of iron oxides. As the housing material (304L) cannot be easily changed, various coating solutions enhancing the passivation of the steels were investigated. Sol–gel lanthanum coatings show the best behavior when tested by TGA at 800 °C. However, in situ monitoring of the oxygen consumption by an oxygen sensor close to operating condition shows that it was not enough protective. [ABSTRACT FROM AUTHOR]

Corynebacterium glutamicum, a gram-positive and facultative anaerobic bacterium, is widely used for the industrial production of amino acids, such as l-glutamate and l-lysine. C. glutamicum grows and produces amino acids under aerobic conditions. When restricted under anaerobic conditions, it produces organic acids, such as l-lactate and succinate, through metabolic shift. With the increasing threat of global warming, these organic acids have drawn considerable attention as bio-based plastic monomers. In addition to the organic acids, the anaerobic bioprocess is also used to produce other value-added compounds, including isobutanol, ethanol, 3-methyl-1-butanol, 2,3-butanediol, l-alanine, and l-valine. Therefore, C. glutamicum is now a versatile cell factory for producing a wide variety of useful chemicals under both aerobic and anaerobic conditions. The growth and metabolism of the bacterium depend on the oxygen levels, which modulate the rearrangement of the carbon flux by reprogramming gene expression patterns and intracellular redox states. Anaerobic cell growth and l-lysine production as well as aerobic succinate production have been demonstrated by engineering the metabolic pathways or supplying a terminal electron acceptor instead of oxygen. In this review, we discuss the physiological and metabolic changes in C. glutamicum associated with its application as a cell factory under different oxygen states. Physiological switching in bacteria is initiated with the sensing of oxygen availability. While such a sensor has not been identified in C. glutamicum yet, the molecular mechanism for oxygen sensing in related bacteria is also discussed. Key Points: • C. glutamicum produces a wide variety of useful compounds under anaerobic conditions. • C. glutamicum is a versatile cell factory under both aerobic and anaerobic conditions. • Metabolic fate can be overcome by engineering metabolic pathways. [ABSTRACT FROM AUTHOR]

Assessment of bacterial growth is an essential tool in many fields of study. Numerous methods are available for that purpose, but they are not without disadvantages. The present study aimed to investigate the application of a water soluble oxygen sensor [Ru(dpp(SO3Na)2)3]Cl2x6H2O (RuBPS) in physiological and biochemical studies of Pectobacterium spp. and other bacteria in 96-well microplate systems. The method was optimized with respect to compound concentration, microplate type, and measurement parameters. The growth of bacteria was assessed under increased salinity, acidic and alkaline pH, decreased water availability, and osmotic stress. Utilization of various sugars by bacteria as the only carbon source and the usefulness of RuBPS in antibiotic susceptibility assays were also investigated. The studies confirmed that the respirometry assay can be successfully used to assess bacterial growth in place of the optical density measurement and the resazurin assay, or in conjugation with those methods. The assay is of special value when growth media are non-homogeneous, bacteria produce reductive compounds during growth, or when bacteria do not grow well in the medium of choice. It may be used to study adaptation potential of plant pathogenic bacteria and other bacteria, and their possible spread into new ecological niches. [ABSTRACT FROM AUTHOR]

The spectral and luminescent properties of new complexes of lutetium(III)–chloride with 5,10,15,20-tetraphenylporphine and its mono-nitrophenyl derivative with a para-nitro group on one of the meso-phenyl rings were studied. The complexes showed weak fluorescence (φfl = 5·10–4) and moderate phosphorescence (φphosph = 3·10–2) at 77 K and phosphorescence at room temperature. The type of extra ligand (monodentate chloride and bidentate acetylacetonate) and the presence of an electron-withdrawing NO2 group on the meso-phenyl ring did not have an appreciable effect on the photophysics of the Lu(III)-porphyrins. The phosphorescence spectra of the complexes were shifted to the long-wavelength region. The phosphorescence lifetimes were longer (2800–3100 μs) than those of the known oxygen sensors Pt(II)- or Pd(II)-porphyrins. The oxygen determination limit in solution was estimated from quenching of the Lu(III)-porphyrin phosphorescence. [ABSTRACT FROM AUTHOR]

We propose a new method for sampling organic substances (for example, hyaluronic acid) from an elastic surface of a solid body (imitation of human skin) to the surface of a sampler. The amount of the sampled substance is determined. A possibility of using this method in cosmetology is shown. [ABSTRACT FROM AUTHOR]

Metallic lead (Pb) has been electrodeposited on FTO substrate at room temperature from aqueous nitrate solution under constant applied potential in the range of − 0.46 to − 0.8 V vs. SCE. Cyclic voltammetry shows that 3D nucleation and growth are the main feature at higher electrolyte concentration when the profile is recorded at 20 mVs−1. While a single step potential facilitates the deposition of faceted crystals of Pb, distinguished lead having cabbage-like morphology can be deposited by applying sequential two step potentials. The I-t response shows that the deposition is initiated through instantaneous 2D nucleation and growth at the shorter time domain followed by 3D nucleation and growth in 0.4 M Pb(NO3)2. Theoretical simulation of the closely matched experimental I-t profile for simple step potential provides a 2D rate constant of 2.00 ± 0.04 × 10−7 mol cm−2 s−1 while for 3D, the vertical and plane growth rate constant of 3.27 ± 0.05 × 10−5 mol cm−2 s−1 and 2.00 ± 0.04 × 10−7 mol cm−2 s−1, respectively. The formation of the cabbage morphology has been discussed on the basis of time evaluation of FE-SEM. The high surface area of unique lead deposits with cabbage morphology shows better life time and oxygen sensitivity in a typical oxygen sensor application.ᅟ [ABSTRACT FROM AUTHOR]

A conventional solid-state reaction was used to synthesize La0.8Sr0.2(Ga0.8Mg0.2)xCo1-xO3-δ (LSGMC, x = 0.1, 0.3, 0.5, 0.7, and 0.9) and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM), of which the structure, conductivity, and thermal expansion behavior were investigated by XRD, four-terminal method, and dilatometry. A limiting current oxygen sensor was prepared with LSGM solid electrolyte and La0.8Sr0.2(Ga0.8Mg0.2)0.1Co0.9O3-δ (LSGMC9) dense diffusion barrier. The effects of temperature, oxygen concentration, and thickness of dense diffusion barrier (L) on sensing properties were investigated. XRD results show that cubic and monoclinic phases are identified for LSGM and LSGMC, respectively. Electrical conductivity increases with x. A change of electrical conductivity from semiconductive to metallic conduction is observed for x = 0.5–0.9 with the temperature rise. Thermal expansion coefficients (TECs) increase to a maximum firstly and then decrease with increasing x at temperature from 300 to 1000 °C. I-V curves of oxygen sensor display a good limiting current plateau. The relationship between limiting current and oxygen concentration is linear. The limiting current decreases with increasing L. [ABSTRACT FROM AUTHOR]

The present investigation has been carried out to optimize the pH level of lanthanum (La)-doped tin dioxide (SnO) nanoparticles towards the potential application in gas sensor. The La-doped SnO nanoparticles were synthesized by sol-gel method in different pH values varying from acidic to base nature. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), ultraviolet (UV), photoluminescence (PL), and scanning electron microscopy (SEM) techniques. The XRD, UV, and PL analyses show the pH influences on the crystallite size of La-doped SnO nanoparticles. The SEM images show the formation of porous structure at pH 11. Also, the electrical conductivity of 1 mol% La-doped SnO at pH 3 and pH 11 were measured by impedance analyzer. In addition, we have fabricated and demonstrated device performance of synthesized La-doped SnO nanoparticles for gas-sensing application. Real-time current response and long-time response to the gas sensing were also studied for the fabricated device. [ABSTRACT FROM AUTHOR]

A systematic structure-photoproperties relationship study of the interactions of porphyrin-fullerene dyads with molecular oxygen was conducted on a set of three porphyrin-fullerene dyads, as this approach of related applications - oxygen sensitivity and photo-induced singlet oxygen generation - of such dyads remained to be endeavoured. To promote energy transfers between the porphyrin and fullerene units and limit undesired charge separation, a particular attention was devoted to the choice of the solvents for the photoproperties determination. Toluene, in which in addition the compounds investigated are not aggregated, was selected accordingly. The molecular orbital levels and energy gaps of the dyads were determined by electrochemistry and theoretical calculations. Their ground state absorption, steady-state fluorescence-based oxygen sensitivity and photo-induced singlet oxygen generation were determined. The dyads were designed to benefit from a facilitated synthetic porphyrin-fullerene coupling thanks to an easy access to formyl-functionalized porphyrins. The effect of two structural parameters was investigated: the presence of electron-donating hexyloxy chains at the para position of the meso-phenyl, and the presence of a phenylacetylene spacer. This latest factor appeared to have the most predominant effect on all these properties. [ABSTRACT FROM AUTHOR]

Stereo Particle Image Velocimetry (SPIV) is used to measure the highly turbulent flow in the upstream region of the catalytic converter for a four stroke IC engine. These experiments are conducted for a motorized engine to investigate the feasibility of using SPIV for exhaust flow measurements in a firing IC engine in our future research. The results obtained here can also be used for validation of the CFD models. The measured flow is highly three dimensional, non-uniform with large magnitudes of turbulence indicating recirculating flow structures. These structures show signatures of jet flows coming out of the exhaust valves at all exhaust crank angles. The triangular shape and location for the end face of each exhaust runner pipe, the length and geometry of the runners also affect the flow mixing process upstream of the catalytic converter contributing to the complexity of this flow. Although majority of the exhaust flow passes through the catalytic converter, some will recirculate due to impingement of the exhaust jets on the surface of the catalyst. [ABSTRACT FROM AUTHOR]

LaSr(GaMg)FeO (LSGMF, x = 0.2-0.9) was prepared by a solid-state reaction method, and the characterization was investigated. Limiting current oxygen sensors were fabricated with LaSrGaMgO (LSGM) as solid electrolyte and LaSr(GaMg)FeO (LSGMF9) as dense diffusion barrier. The influences of temperature, oxygen concentration, and the thickness of dense diffusion barrier ( L) on sensing properties of oxygen sensors were investigated. The results show that the crystal structure of samples is perovskite. The electrical conductivity increases with increasing x. A transition from semiconductive to pseudometallic behavior which is associated with oxygen losses from the lattice is observed with an increase of temperature for x = 0.3, 0.5, and 0.7. The thermal expansion coefficient (TEC) in the temperature range 300-1000 °C increases to a maximum and then decreases with increasing x. TECs between LSGMF9 and LSGM are close. The limiting current oxygen sensor exhibits an excellent sensing performance, and the limiting current responses depend linearly on the oxygen concentration. As the L value increases, the limiting current decreases. The polarization resistance of the sensor decreases with increasing oxygen concentration. [ABSTRACT FROM AUTHOR]

The oxidation behaviors of the Fe, Fe-15mass%Cr and Fe-30mass%Cr alloys were investigated at 1173 K in Ar-HO and Ar-O-HO atmospheres using an oxygen sensor and a hydrogen sensor installed at the outlet of an experimental reactor. In Ar-HO, the changes in the hydrogen partial pressure were continuously measured using the hydrogen sensor, and the amounts of generated hydrogen and resultant consumed oxygen were calculated. The calculated gross mass gain was in close agreement with that gravimetrically obtained after the experiment. In Ar-O-HO, the amount of oxygen consumed from the ambient oxygen gas in the atmosphere was calculated from the change in the oxygen partial pressure measured using the oxygen sensor. In this case, the gross mass gain was analyzed as the sum of the amount of oxygen consumed from the ambient oxygen and that supplied from the steam dissolution. The oxidation patterns were classified into three types: (1) water vapor oxidation (in Ar-HO), (2) water vapor oxidation and oxygen oxidation (in Ar-500 ppmO-HO except for Fe-30Cr), and (3) oxygen oxidation (in Ar-1%O-HO). It was demonstrated that a gas monitoring method using a combination of hydrogen and oxygen sensors is useful for investigating the water vapor oxidation in an atmosphere containing water vapor and oxygen. [ABSTRACT FROM AUTHOR]

We describe a maskless photopolymerization technique for integration of luminescent sensors for determination of pH values and dissolved oxygen (DO) into commercially available all-glass microfluidic reactors (in sizes as small as 43 ± 3 μm for both DO and pH sensors). The sensor spots are poly(ethyleneglycol acrylate)-based and obtained by photopolymerization of oligomers in the presence of optical probes for oxygen and pH values, respectively. The resulting devices were applied to in-line monitoring of enzymatic conversions of acetylcholine and glucose (by using acetylcholine esterase and glucose oxidase, respectively) on the microscale. The detection limits are 258 μM and 505 μM for acetylcholine and glucose, respectively. The method has a large potential in terms of monitoring enzymatic and other chemical reactions on the microscale in that it does not require special instrumentation apart from a standard widefield fluorescence microscope. [ABSTRACT FROM AUTHOR]

The article describes the preparation of chitosan-coated hemoglobin (Hb-CS) microcapsules by (a) preparing a CaCO precipitate containing Hb, (b) crosslinking Hb with glutaraldehye, (c) coating the particles with chitosan, and (d) preparing Hb-CS microcapsules by removing the CaCO template with a solution of disodium EDTA. The morphology and electrochemical properties of the Hb-CS microcapsules were investigated by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. An oxygen sensor was obtained by immobilizing the Hb-CS microcapsules on the surface of a glassy carbon electrode (GCE) first modified with gold nanoparticles. The application of Hb-CS microcapsules facilitates electron transfer on the surface of GCE and warrants the integrity and biological activity of Hb. The oxygen sensor, operated best at a working voltage of −0.335 V (vs. SCE), displays a low limit of detection (30 nM). The Hb-CS microcapsules also are shown to release loaded oxygen to an anaerobic aqueous environment within 300 min. [ABSTRACT FROM AUTHOR]

The LaSr(GaCo)MgO (LSGMC x = 0.05, 0.1, 0.15, 0.2, 0.25) and LaSr(GaFe)MgO (LSGMF x = 0.1, 0.2, 0.3) samples were prepared by solid-state reaction. The structure, conductivity, thermal expansion behavior, and chemical compatibility were studied by XRD, dilatometry, and four-terminal method. A limiting current oxygen sensor was prepared with LaSrGaMgO as a solid electrolyte and LaSr(GaCo)MgO as a dense diffusion barrier. The oxygen-sensitive characteristic was measured at different oxygen concentrations. The results show that the phase structure of samples is cubic, except LaSr(GaCo)MgO, which has a hexagonal structure. The change in activation energy for electrical conductivity and the increase in thermal expansion coefficient are confirmed to correlate with an increasing concentration of oxygen vacancies. The limiting current oxygen sensor exhibits a good limiting current platform and the limiting current depends linearly on the oxygen concentration: I(mA) = 12.8519 + 2.2667 $$x_{{\text{O}_{\text{2}} }}$$ (mol%, 0 < $$x_{{{\text{O}}_{ 2} }}$$ < 3.31) at 750 °C, I(mA) = 14.3222 + 3.5180 $$x_{{\text{O}_{\text{2}} }}$$ (mol%, 0 < $$x_{{{\text{O}}_{ 2} }}$$ < 4.16) at 800 °C, and I(mA) = 15.2872 + 5.0269 $$x_{{\text{O}_{\text{2}} }}$$ (mol%, 0 < $$x_{{{\text{O}}_{ 2} }}$$ < 4.12) at 850 °C. The sensor has the best sensitivity at 850 °C. As the oxygen concentration increases, the interface resistance of the sensor decreases at 850 °C. [ABSTRACT FROM AUTHOR]

Paper-based scaffolds are an attractive material for generating 3D tissue-like cultures because paper is readily available and does not require specialized equipment to pattern, cut, or use. By controlling the exchange of fresh culture medium with the paper-based scaffolds, we can engineer diffusion-dominated environments similar to those found in spheroids or solid tumors. Oxygen tension directly regulates cellular phenotype and invasiveness through hypoxia-inducible transcription factors and also has chemotactic properties. To date, gradients of oxygen generated in the paper-based cultures have relied on cellular response-based readouts. In this work, we prepared a luminescent thin film capable of quantifying oxygen tensions in apposed cell-containing paper-based scaffolds. The oxygen sensors, which are polystyrene films containing a Pd(II) tetrakis(pentafluorophenyl)porphyrin dye, are photostable, stable in culture conditions, and not cytotoxic. They have a linear response for oxygen tensions ranging from 0 to 160 mmHg O, and a Stern-Volmer constant ( K) of 0.239 ± 0.003 mmHg O. We used these oxygen-sensing films to measure the spatial and temporal changes in oxygen tension for paper-based cultures containing a breast cancer line that was engineered to constitutively express a fluorescent protein. By acquiring images of the oxygen-sensing film and the fluorescently labeled cells, we were able to approximate the oxygen consumption rates of the cells in our cultures. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A basic zirconia oxygen sensor was utilized to monitor the gas-solid oxidation reaction characteristics of metal/metal-oxide powder beds. The method described allowed for simple determination of chemical reaction rate constants for the oxidation reactions. The signal output of the sensor was analyzed for oxidation of the powder bed and diffusion of oxygen into the powder bed. The oxygen transport mechanisms occurring inside the sensor were described to further understand the signal outputs from the powder bed, and a discussion of relevant thermodynamic and kinetic theory was provided. Two metal/metal-oxide systems were examined using this device to demonstrate its performance. The simple Ni/NiO system was chosen to demonstrate feasibility, and the complex W/WO system was chosen to demonstrate versatility of the sensor. Combining the experimental data with relevant kinetic theory, chemical reaction rate constants were calculated from plots of sensor ocv versus time for each reaction step during the metal oxidation sequences. [ABSTRACT FROM AUTHOR]

A drop in oxygen partial pressure results in elevation of blood vessel diameter. It has been demonstrated that isolated vessels exhibit this unique feature only when they are perfused in the presence of erythrocytes. More recently, it was shown that haemoglobin plays a key role in oxygen sensing. Its deoxygenated form interacts with band 3 protein, triggering the cascade of non-identified intracellular signals involved in nitric oxide production and release of ATP interacting with P2Y purinergic receptors in endothelial cells. In this review, we summarize the data on mechanisms of ATP release from erythrocytes, as well as on its physiological and pathophysiological implications. [ABSTRACT FROM AUTHOR]

We are presenting a microfluidic droplet-based system for non-invasive, simultaneous optical monitoring of oxygen during bacterial cultivation in nL-sized droplets using ~350 nm nanobeads made from polystyrene and doped with the NIR-emitting oxygen probe platinum (II) 5, 10, 15, 20- meso-tetraphenyltetrabenzoporphyrin (PtTPTBP). Data were readout by a two-channel micro flow-through fluorimeter and a two-channel micro flow-through photometer. The time-resolved miniaturized optical multi endpoint detection was applied to simultaneously sense dissolved oxygen, cellular autofluorescence, and cell density in nL-sized segments. Two bacterial strains were studied that are resistant to heavy metal ions, viz. Streptomyces acidiscabies E13 and Psychrobacillus psychrodurans UrPLO1. The study has two main features in that it demonstrates (a) the possibility to monitor the changes in oxygen partial pressure during metabolic activity of different bacterial cultures inside droplets, and (b) the efficiency of droplet-based microfluidic techniques along with multi-parameter optical sensing for highly resolved microtoxicological screenings in aquatic systems. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Oxygen-sensitive photoluminescence intensity of a new combination of luminophore and matrix has been investigated for use in pressure sensitive paint applications. In consideration of oxygen permeability as well as optical transparency and structural stability, a fluorinated acrylate polymer is chosen as matrix in this study, where PtTFPP complex is dispersed and acts as luminophore responsible for the oxygen quenching. Processing conditions as to spin-coat films of the fluorinated acrylate doped with the PtTFPP are described. Pressure dependence of the photoluminescence emission of such spin-coat films is explained in connection with luminophore concentration, film thickness and types of substrate. [ABSTRACT FROM AUTHOR]

In this paper, a highly sensitive electrochemical sensor for dissolved oxygen was prepared. A glassy carbon electrode was modified with silver nanodendrites that were synthesized by electrochemical deposition on the electrode without the use of a surfactant or template. The electrode displayed efficient electrocatalytic reduction of dissolved oxygen to form hydroxy ions via a four-electron reduction pathway, and a significant decrease in the respective overvoltage. The sensor responded linearly to dissolved oxygen in the 1.0-66.7 μM concentration range, and had a remarkably good sensitivity (0.169 μA μM) at an applied potential of −300 mV (vs. Ag/AgCl). The lower detection limit was 0.043 μM (at the signal-to-noise ratio of 3), and the response time was 5 s. The good performance was attributed to the enlarged electro-active surface of the dendritic silver nanostructures and to the efficiency of electron transfer between dissolved oxygen and the electrode. The sensor also showed good reproducibility, long-term stability, and relative good selectivity. [ABSTRACT FROM AUTHOR]

MoO nanobelts (NBs) having different properties have been synthesized via a physical vapor deposition (PVD) method. The crystallographic structures and morphologies of the NBs were characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. Electrical measurements were performed and the profound piezoresistive effect in MoO experimentally studied and verified. Factors that influence the gauge factor, such as NB size, doping concentration and atmosphere composition, are discussed and analyzed. Gas sensing performance was also tested in devices and it was demonstrated that by applying strain to the gas sensor, its sensing performance could be effectively tuned and enhanced. This study provides the first demonstration of significant piezoresistivity in MoO NBs and the first illustration of a generic mechanism by means of which this effect can be coupled with other electronic modulation measures to afford better device performance and broader material functionality. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Multi-walled-carbon-nanotubes/polyvinylacetate/titanium oxide (MWCNTs/PVAc/TiO) composite fibers with different MWCNT loadings were prepared using the electrospinning technique. The addition of cetyl trimethyl ammonium bromide (CTAB) as a surfactant agent to promote the dispersion of the MWCNTs was also evaluated. The morphological and microstructural properties of as-spun and annealed samples in air at 600°C were examined using thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and x-ray diffraction (XRD). The sensing characteristics of the synthesized TiO-based nanostructures were evaluated for oxygen monitoring at moderate temperatures. The effects of the MWCNT loading, the addition of the surfactant and the composition of the TiO crystalline phases were investigated and discussed. [ABSTRACT FROM AUTHOR]

This work investigates a novel usage of aluminum-doped ceria nanoparticles (ADC-NPs), as the molecular probe in optical fluorescence quenching for sensing the dissolved oxygen (DO). Cerium oxide (ceria) nanoparticles can be considered one of the most unique nanomaterials that are being studied today due to the diffusion and reactivity of oxygen vacancies in ceria, which contributes to its high oxygen storage capability. Aluminum can be considered a promising dopant to increase the oxygen ionic conductivity in ceria nanoparticles which can improve the sensitivity of ceria nanoparticles to DO. The fluorescence intensity of ADC-NPs, synthesized via chemical precipitation, is found to have a strong inverse relationship with the DO concentration in aqueous solutions. Stern-Volmer constant of ADC-NPs at room temperature is determined to be 454.6 M, which indicates that ADC-NPs have a promising sensitivity to dissolved oxygen, compared to many presently used fluorophores. In addition, Stern-Volmer constant is found to have a relatively small dependence on temperature between 25 °C to 50 °C, which shows excellent thermal stability of ADC-NPs sensitivity. Our work suggests that ADC-NPs, at 6 nm, are the smallest diameter DO molecular probes between the currently used optical DO sensors composed of different nanostructures. This investigation can improve the performance of fluorescence-quenching DO sensors for industrial and environmental applications. [ABSTRACT FROM AUTHOR]

New sensing materials have been developed which rely on the use of luminescent europium(III) and gadolinium(III) complexes with thenoylacetylacetonate embedded in an acridone-polystyrene conjugate. Acridone acts as an antenna which efficiently absorbs violet light. Covalent coupling to the polystyrene backbone prevents aggregation and enables very high antenna loading (16 % w/ w). Energy transfer from the antenna to the lanthanide complexes results in efficient red luminescence from the Eu(III) complex or green phosphorescence originating from the Gd(III) chelate. The luminescence of the material based on the Eu(III) complex is only slightly affected by oxygen but is highly sensitive to temperature under physiological conditions (20-40 °C). The Gd(III) complex has long phosphorescence decay times of approximately 1 ms and high sensitivity to oxygen. Ultra-thin (250 nm) sensing layers with sufficient absorption at the excitation wavelength enable monitoring of rapid oxygen changes virtually in real time. Immobilization of both complexes in a single matrix results in a dual-luminescence material with emissions almost ideally matching the red and green channels of a digital camera. Thus, oxygen imaging using a very simple and inexpensive set-up can be realized. Additionally, the material can be used for simultaneous sensing of oxygen and temperature. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A portable instrument for oxygen determination, based on the quenching of phosphorescent octaethylporphyrin by gaseous O, has been developed using the fluorimetric paired emitter-detector diode technique (FPEDD). The instrument configuration consists of two light-emitting diodes (LEDs) facing each other, with an interchangeable support containing a phosphorescent membrane in between, in which one of the LEDs is used as the light source (emitter LED) and the other, working in reverse bias mode, as the light detector. The feasibility of using a LED as a luminescence detector is studied. Its small size enables integration of the instrument into a portable measurement system. A systematic study of the system capabilities as a portable instrument was performed to optimize range, sensitivity, short term and long term stability, dynamic behaviour, effect of temperature and humidity, and temporal drift. [ABSTRACT FROM AUTHOR]

Magnetic optical sensor particles were prepared using a mini-emulsion solvent evaporation (MESE) technique. The resulting nanoparticles (NPs) have diameters around 100 nm and relatively narrow size distribution ( PDI < 0.2). Incorporation of probes for oxygen or pH resulted in magnetic sensor particles for bioprocess monitoring and imaging applications. The MESE technique yields sensing NPs in higher quantities than obtained by a previously reported nanoprecipitation method, and the size of the NPs is smaller than that of particles made by spray-drying of sensor cocktails. Moreover, the technique is flexible in terms of polymers, solvents and indicators used in that it may be applied-at least in principle-to numerous combinations of two-phase systems. [ABSTRACT FROM AUTHOR]

Thin films of ionic conductors have low internal resistance. Hence, it could be used as an electrolyte material in sensors to operate at ambient temperatures. Cerium fluoride, a unipolar fluoride ion conductor, has got a different application in electrochemical sensor. In the present work, cerium fluoride thin films have been prepared by physical vapor deposition method and their electrical properties are studied. X-ray diffraction studies reveal the polycrystalline nature of the prepared thin films and the structure of the material. Scanning electron microscopy (SEM) images show grain-like structures. Conductivity analysis of the thin films has been studied by ac impedance analysis and the maximum conductivity value is found to be 1.04 × 10−6 S cm−1. The impedance spectra emphasize intergranular conduction in the prepared thin films. [ABSTRACT FROM AUTHOR]

Polypyridyl ruthenium (Ru) complexes 1–3 were prepared. Their photophysical properties were investigated by UV-Vis absorption and luminescence emission spectra. The luminescent lifetimes of these Ruthenium complex were prolonged by more than 5 folds (τ = 2.50 μs for complex 3) when compared with the parent Ru complex 1 (τ = 0.45 μs). We propose that the extended luminescent lifetime of complex 3 is due to the equilibrium between 3MLCT state and the pyrene localized 3π-π* triplet state (3IL). The luminescent O2-sensing property of the complexes in solution and the IMPEK-C polymer film were studied, and the O2 sensing was quantified with the two-site model. The oxygen-sensing property of the Ru complexes can be improved by 104-fold with extension of the luminescent lifetimes. For example, the quenching constant KSV was improved from 0.0023 Torr−1 of 1 to 0.2393 Torr−1 for 3. Our results demonstrated a versatile approach for the preparation of Ru (II) polypyridine complexes with extended luminescent lifetimes as functional materials, for example, for luminescent oxygen-sensing applications. [ABSTRACT FROM AUTHOR]

Lithium octa- n-butoxynaphthalocyanine (LiNc-BuO) is a promising probe for biological electron paramagnetic resonance (EPR) oximetry and is being developed for clinical use. However, clinical applicability of LiNc-BuO may be hindered by potential limitations associated with biocompatibility, biodegradation, and migration of individual crystals in tissue. To overcome these limitations, we have encapsulated LiNc-BuO crystals in polydimethyl siloxane (PDMS), an oxygen-permeable and bioinert polymer, to fabricate conveniently implantable and retrievable oxygen-sensing chips. Encapsulation was performed by a simple cast-molding process, giving appreciable control over size, shape, thickness and spin density of chips. The in vitro oxygen response of the chip was linear, reproducible, and not significantly different from that of unencapsulated crystals. Cast-molding of the structurally-flexible PDMS enabled the fabrication of chips with tailored spin densities, and ensured non-exposure of embedded LiNc-BuO, mitigating potential biocompatibility/toxicological concerns. Our results establish PDMS-encapsulated LiNc-BuO as a promising candidate for further biological evaluation and potential clinical application. [ABSTRACT FROM AUTHOR]

The use of oxygen-sensing water-insoluble paramagnetic probes, such as lithium octa- n-butoxynaphthalocyanine (LiNc-BuO), enables repeated measurements of pO2 from the same location in tissue by electron paramagnetic resonance (EPR) spectroscopy. In order to facilitate direct in vivo application, and hence eventual clinical applicability, of LiNc-BuO, we encapsulated LiNc-BuO microcrystals in polydimethylsiloxane (PDMS), an oxygen-permeable and bioinert polymer, and developed an implantable chip. In vitro evaluation of the chip, performed under conditions of sterilization, high-energy irradiation, and exposure to cultured cells, revealed that it is biostable and biocompatible. Implantation of the chip in the gastrocnemius muscle tissue of mice showed that it is capable of repeated and real-time measurements of tissue oxygenation for an extended period. Functional evaluation using a murine tumor model established the suitability and applicability of the chip for monitoring tumor oxygenation. This study establishes PDMS-encapsulated LiNc-BuO as a promising choice of probe for clinical EPR oximetry. [ABSTRACT FROM AUTHOR]

In research, pharmacologic drug-screening and medical diagnostics, the trend towards the utilization of functional assays using living cells is persisting. Research groups working with living cells are confronted with the problem, that common endpoint measurement methods are not able to map dynamic changes. With consideration of time as a further dimension, the dynamic and networked molecular processes of cells in culture can be monitored. These processes can be investigated by measuring several extracellular parameters. This paper describes a high-content system that provides real-time monitoring data of cell parameters (metabolic and morphological alterations), e.g., upon treatment with drug compounds. Accessible are acidification rates, the oxygen consumption and changes in adhesion forces within 24 cell cultures in parallel. Addressing the rising interest in biomedical and pharmacological high-content screening assays, a concept has been developed, which integrates multi-parametric sensor readout, automated imaging and probe handling into a single embedded platform. A life-maintenance system keeps important environmental parameters (gas, humidity, sterility, temperature) constant. [ABSTRACT FROM AUTHOR]

A series of platinum meso-tetrakis [3-methoxy-4-(N-carbazyl)n-alkyloxyphenyl]porphyrin (Pt-4Cn-TPP, n = 4, 6 and 8) are synthesized. Pt-4C4-TPP, Pt-4C6-TPP and Pt-4C8-TPP exhibit similar luminescent properties in solution and solid state. Three protonated platinum (II) porphyrins are assembled with mesoporous silica MCM-48, respectively, resulting in assembly materials Pt-4Cn-TPP4+/ MCM-48 (n = 4, 6 and 8). The luminescent intensity of Pt-4Cn-TPP4+/MCM-48 can be extremely quenched by molecular oxygen with high sensitivity (I0/I100 > 9). The Stern-Volmer plots of these assembly materials display considerable linearity within a wide range of oxygen concentration (0 to 100%). The response time is all ⩽ 1 s and recovery time ⩽ 22 s for these assembly materials. [ABSTRACT FROM AUTHOR]

A new online monitoring technique to measure the physiological parameters, dissolved oxygen (DO) and pH of microbial cultures in continuously shaken 24-well microtiter plates (MTP) is introduced. The new technology is based on immobilised fluorophores at the bottom of standard 24-well MTPs. The sensor MTP is installed in a sensor dish reader, which can be fixed on an orbital shaker. This approach allows real online measurements of physiological parameters during continuous shaking of cultures without interrupting mixing and mass transfer like currently available technologies do. The oxygen transfer conditions at one constant shaking frequency (250 1/min) and diameter (25 mm) was examined with the chemical sulphite oxidation method. Varied filling volumes (600–1,200 μL) of Escherichia coli cultures demonstrated the importance of sufficient oxygen transfer to the culture. Cultures with higher filling volumes were subjected to an oxygen limitation, which influenced the cell metabolism and prolongated the cultivation time. The effects could be clearly monitored by online DO and pH measurements. A further study of different media in an E. coli fermentation elucidated the different growth behaviour in response to the medium composition. The MTP fermentations correlated very well with parallel fermentations in shake flasks. The new technique gives valuable new insights into biological processes at a very small scale, thus enabling parallel experimentation and shorter development times in bioprocessing. [ABSTRACT FROM AUTHOR]

Calorimetric methods are used in combination with online oxygen measurement (using an amperometric sensor) and determination of the optical density (using a fibre optic sensor) to investigate microbial growth behaviour. The calorimetric curves of different batch experiments show a characteristic and reproducible course. Changes in the slope of the Δ T–time curves indicate the effects of limiting factors on the microbial activity during the cultivation. A first limitation could be correlated with the depletion of oxygen in the medium; a second correlates with the depletion of the carbon source. Measurements of optical density in some cases provide reliable information about the growth of a microorganism culture. Our measurements show a good correlation of the universal calorimetric signal (heat–time curve) to the signal of the miniaturised photometric (OD) sensor. [ABSTRACT FROM AUTHOR]

Hypoxia-inducible factor (HIF), a transcriptional complex conserved from Caenorhabditis elegans to vertebrates, plays a pivotal role in cellular adaptation to low oxygen availability. In normoxia, the HIF-α subunits are targeted for destruction by prolyl hydroxylation, a specific modification that provides recognition for the E3 ubiquitin ligase complex containing the von Hippel-Lindau tumour suppressor protein (pVHL). Three HIF prolyl-hydroxylases (PHD1, 2 and 3) were identified recently in mammals and shown to hydroxylate HIF-α subunits. Here we show that specific 'silencing' of PHD2 with short interfering RNAs is sufficient to stabilize and activate HIF-1α in normoxia in all the human cells investigated. 'Silencing' of PHD1 and PHD3 has no effect on the stability of HIF-1α either in normoxia or upon re-oxygenation of cells briefly exposed to hypoxia. We therefore conclude that, in vivo, PHDs have distinct assigned functions, PHD2 being the critical oxygen sensor setting the low steady-state levels of HIF-1α in normoxia. Interestingly, PHD2 is upregulated by hypoxia, providing an HIF-1-dependent auto-regulatory mechanism driven by the oxygen tension. [ABSTRACT FROM AUTHOR]

Gaseous transport through lenticels is widely accepted to be the main pathway for oxygen supply to the parenchymatous tissues of the wood. Circumstantial evidence exists that the oxygen required for respiration by these living cells can be obtained from the transpiration stream. However, there has been no functional confirmation of this role. To address this problem and to quantify the contribution of the different pathways to the oxygen supply of the sapwood, we have developed a three-electrode miniaturized oxygen-selective sensor to be implanted into the sapwood for long-term determination of the oxygen concentration. In spring, during the active growing season, the oxygen concentration of the sapwood of young olive (Olea europaea L.) trees changed from 80–90 μmol O2 l-1 around midday to 20–30 μmol O2 l-1 in the night. These concentrations correspond to a deficit of oxygen for the sapwood between 65–70% and 88–90% of an aqueous solution saturated with air. In the daylight hours, almost all the oxygen present in the sapwood was delivered by the transpiration stream, driven by the soil–plant–atmosphere water-potential gradient. During the night the diffusion of oxygen via the sap-filled lumina of the tracheids and vessels (xylary diffusion in the aqueous phase) accounted for about 87% of all the oxygen present, whereas only the remaining 13% was assessed as supplied by radial diffusion in the aqueous or gaseous phase. [ABSTRACT FROM AUTHOR]

Heating 5at.% (on A-site) La-doped SrTiO3(100) single crystals in an ambient atmosphere at 1300°C for 120 h results in the formation of insulating islands on top of the surface with typical dimensions of up to 50 μm. The islands and the surface between them were investigated by spectroscopic Metastable Impact Electron Emission Microscopy (specMIEEM) and Photoelectron Emission Microscopy in order to determine its electronic and geometric structure. The comparison of specMIEEM results with MIES (Metastable Impact Electron Spectroscopy) spectra from stoichiometric SrO shows that the insulating islands, which most likely consist of SrO, are at least partly covered by another species, probably SrO2. All these islands are surrounded by 2–3 μm wide haloes. The electronic structure of these haloes is quite different from that of SrO and SrTiO3 but similar to the electronic structure of TiO2 or Ti2O3. It is suggested that the depletion of SrO from Ruddlesden-Popper (Sr n + 1Ti nO3 n + 1) phases results in the formation of SrO islands. [ABSTRACT FROM AUTHOR]

An ultralow oxygen partial pressure-controlling system, based on solid-stateelectrochemical principles, has been developed. This system consists of anoxygen sensor and an oxygen pump and is controlled by a PC computer. Theoxygen sensor is used to measure the oxygen partial pressure in an enclosedsystem, while the oxygen pump is used to transport oxygen from the ambientair into the enclosed system or from the enclosed system to the ambientair. The operating conditions of this system have been studied. The resultsshowed that it can be used to establish a stable oxygen partial pressure inthe range of 10−18∼5×105 Pa (1×10−23∼5 atm)in the enclosed system. This system has been used to investigate theselective oxidation of the Cr and the oxide formation on the surface of aNi–Cr alloy under three different low oxygen partial pressures. Theoxide morphology was studied using atomic force microscopy (AFM). The resultsagreed well with those in the literature and also confirm the reliability of this system. [ABSTRACT FROM AUTHOR]

Thin films of the non-stoichiometric perovskite SrFeO2.5+x have been grown by the pulsed excimer laser deposition technique onto sapphire substrates. The electrical conductance properties of the thin films have been determined in a series of experiments done both isothermally and with programmed temperature changes from ambient to 490°C and under O2/N2 atmospheres with oxygen concentrations in the range from 100 ppm to 100%. Over these ranges of temperature and oxygen partial pressure a wide range of oxygen stoichiometry in SrFeO2.5+x occurs (approximately 0 < x < 0.5), which includes all four known phases in the SrFeO2.5 + x + O2 system. The experimentally measured values for the activation energy of conduction, εA, for SrFeO2.5+x films at temperatures 100 < T < 200°C are in the range 0.30 < εA < 0.47 eV under oxygen at partial pressures 0.001 O 2)< 0.05 atm and 0.18 < εA < 0.28 eV for 0.2 O 2)< 1 atm. These values for εA are typical for compositions of SrFeO2.5+x with stoichiometries in the range 0.25 < x < 0.45. For T < 300°C and for P(O 2)< 0.001 atm the films were essentially insulators. For T > 250°C and P(O 2)> 0.001 atm, the oxygen stoichiometries of the films change during the programmed temperature ramps. For these conditions, the values δεA/δ T exhibit minima/maxima in the temperature range 250 < T < 320°C which are interpreted as being due to the onset of the order-disorder phase transition from the cubic to the tetragonal and orthorhombic ordered phases of SrFeO2.5+x with oxygen stoichiometry in the range 0.08 < x < 0.38. The SrFeO2.5+x thin films have application as oxygen sensing materials, and a relationship between conductance and oxygen sensitivity, S ox, has been derived. The values of S ox for SrFeO2.5+x thin films increases by more than an order of magnitude for compositions close to the lower stoichiometric limit where the principal phase conversion is between the cubic perovskite and the brownmillerite forms. [ABSTRACT FROM AUTHOR]

Luminescence quenching of Ru(II) complexes by oxygen has proved a powerful method of quantitative oxygen analysis. It has become clear that the polymer support for the sensor molecule plays a pivotal role in the sensor performance. The current work is devoted to understanding how the physical and photophysical properties of a sensor respond to changes in polymer composition. An oxygen quenching study was conducted on [Ru(Ph2phen)3]Cl2(Ph2phen=4,7-diphenyl-1,10-phenanthroline), in copolymer supports consisting of GP-163 (a polydimethylsiloxane (PDMS) with varying amounts of pendant acrylate groups) combined with a number of alkyl methacrylates with long chain alkyl or fluorinated alkyl esters. Increasing the chain length or the degree of fluorination on the hydrocarbon chains enhances performance. However, there is an optimal chain length for the fluorinated hydrocarbons for sensitivity, linearity, and physical properties. Too long a chain yields reduced quenching sensitivity and yields cloudy polymers. All systems showed some degree of heterogeneity as indicated by nonlinear Stern-Volmer quenching plots, but their intensity quenching data could be successfully fit with a two-site model. [ABSTRACT FROM AUTHOR]

Mg-doped SrTio3 thick film sensors fabricated by screen-printing proved to be very promising for the use as oxygen sensors. A study of the influence of water on the response of these sensors gives an important basis for understanding their behavior in practical applications. The influence of water on the sensor response was measured in the oxygen partial pressure region from air (0.21 bar) to pure N2 (2.5 × 10−5)and the temperature range from 600 to 800°C. The relative humidity was varied from 1 to 95% RH. The resistance variation as a function of temperature and the activation energy were evaluated under different dry and wet conditions. The results obtained show that the resistance of these sensors generally decreases with increasing water content in the carrier gas and that the effect of water was strongest at lower temperatures as well as at lower oxygen pressures. To explain this behavior, it is proposed that a partial proton conduction is introduced in the water-containing atmospheres and that this contributes to the total conductivity leading to a reduction of the total resistance. Finally, the measurements also show that the response of these sensors still depends on the oxygen partial pressure according to the standard expression even in the presence of water vapor. Therefore, these sensors can still be used as oxygen sensors in humid atmospheres. [ABSTRACT FROM AUTHOR]