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Organic room temperature phosphorescent (ORTP) materials provide an exciting research direction for phosphorescent oxygen (O2) sensors due to their high sensitivity and rapid response to O2. However, most pure ORTP materials are tightly-packed aromatic compound crystals in a face-to-face manner, which largely prohibits effective O2 diffusion for sensing. Thus, how to solve this contradiction still faces huge challenges. Here, the use of organic phosphorescent indicator carbon dots (CDs), inorganic matrix layered double hydroxides (LDHs) and polymers (PVA) successfully prepared an ultra-long RTP composite film whose phosphorescence decay intensity is linearly related to O2 concentration. More importantly, the use of the abundant O2 defects (Vo) on the surface of the inorganic matrix LDHs to adsorb O2, which further accelerates the phosphorescence quenching of the thin film and improves the O2 response. This strategy will provide the possibility to develop high-sensitivity phosphorescent O2 sensors from a new perspective.

Quantitative oxygen detection is of great importance in biological fields, complex environments, and chemical process engineering. Due to the high sensitivity and rapid response of long-lived phosp...

Oxygen (O2) uptake by cells and tissues is a critical indicator of metabolic demand, changes in microenvironment, and pathophysiology. O2 uptake from the atmosphere accounts for virtually all the O2 consumption in the avascular cornea; however, a detailed spatiotemporal profile of corneal O2 uptake (COU) remains undetermined. Here, we used a non-invasive self-referencing optical fiber O2 sensor—the scanning micro-optrode technique (SMOT)—to report the O2 partial pressure and flux variations at the ocular surface of rodents and non-human primates. In vivo spatial mapping in mice revealed a distinct COU, characterized by a centripetal gradient with a significantly higher O2 influx at the limbus and conjunctiva regions than at the center of the cornea. This regional COU profile was reproduced ex vivo in freshly enucleated eyes. The centripetal gradient was conserved across the following species analyzed: mice, rats, and rhesus monkeys. In vivo temporal mapping in mice showed a significant increase in the O2 flux in the limbus in the evening compared to other times. Altogether, the data unveiled a conserved centripetal COU profile, which may be associated with the limbal epithelial stem cells residing at the intersection of the limbus and conjunctiva. These physiological observations will serve as a useful baseline for comparative studies with contact lens wear, ocular disease, diabetes, etc. Moreover, the sensor may be applied to understand the responses of the cornea and other tissues to various insults, drugs, or changes in the environment.

Chemical sensors are measurement devices that convert a chemical or physical property of a specific analyte into a measurable signal, whose magnitude is normally proportional to the concentration of the analyte [...]

Optical oxygen sensors based on photoluminescence quenching have gained increasing attention as a superior method for continuous monitoring of oxygen in a growing number of applications. A simple and low-cost fabrication technique was developed to produce sensor arrays capable of two-dimensional oxygen tension measurement. Sensor patches were printed on polyvinylidene chloride film using an oxygen-sensitive ink cocktail, prepared by immobilizing Pt(II) mesotetra(pentafluorophenyl)porphine (PtTFPP) in monodispersed polystyrene microparticles. The dispersion media of the ink cocktail, high molecular weight polyvinyl pyrrolidone suspended in 50% ethanol (v/v in water), allowed adhesion promotion and compatibility with most common polymeric substrates. Ink phosphorescence intensity was found to vary primarily with fluorophore concentration and to a lesser extent with polystyrene particle size. The sensor performance was investigated as a function of oxygen concentrations employing two different techniques: a multi-frequency phase fluorometer and smart phone-based image acquisition. The printed sensor patch showed fast and repetitive response over 0-21% oxygen concentrations with high linearity (with R(2) >0.99) in a Stern-Volmer plot, and sensitivity of I(0)/I(21) >1.55. The optical sensor response on a surface was investigated further using two-dimensional images which were captured and analyzed under different oxygen environment. Printed sensor patch along with imaging read-out technique make an ideal platform for early detection of surface wounds associated with tissue oxygen.

In this work, the authors report the fabrication and characterization of CeO2 -HfO2 mixed oxide thin film based oxygen gas sensors. The atomic concentrations of the individual elements Ce and Hf in the mixed oxide (CeO2 -HfO2) thin films were controlled and tuned using a novel method in RF sputtering to achieve better oxygen sensing characteristics. The characteristics of the sensing film were evaluated using various characterization techniques such as TEM-EDS, FESEM-EDS, XPS and XRD. The XPS and EDS data revealed that the Hf concentration increases with an increase in size as well as number of the HfO2 pellets that are placed on a 3-inch CeO2 target during sputtering. From the XRD and XPS analysis, it was found that the mixed oxide film with 10-11% Hf atomic concentration has the best sensing characteristics. The superior sensing characteristics of the CeO2 -HfO2 film can be attributed to the existence of a highly reactive plane (200) with the highest surface energy and a strongly reduced surface with oxygen vacancy formation due to the presence of Ce3+ ions and HfOx, x 2 on the surface of the mixed oxide film. The sensor film detected the presence of oxygen gas even at low temperatures (< 400°C); however, the response time and recovery time were slightly higher. The sensor film of thickness 220 nm with Hf concentration between 10-11% showed excellent sensitivity (~15), fast response and recovery times of 8 s and 10 s respectively at an operating temperature of 400°C, which are the best values reported till date for CeO2 based oxygen sensors.

Sensors have a wide range of applications from industrial production stages to medical respiratory equipment. The oxygen sensor is also one of the essential sensors to follow up the environmental oxygen level for humans. As an example, a 21% oxygen level is necessary to live safely in an environment and this would create a vital risk for a human being after lowering below 16% oxygen levels. Also in OLED production and lithium battery production processes, following and stabilizing the oxygen level below 5 ppm is mandatory in a glove box while production stages go on. Zirconium oxide is a known metal oxide that gives a sensory response to lowered oxygen levels. In this study, all sensor devices were produced over FTO(fluorine-doped tin oxide) glasses. Sol–gel-derived zirconium(IV) oxide chloride was used as an oxygen detection layer. Zirconium(IV) oxide chloride-coated FTO glass sensor worked successfully and gave a small increasing signal response to changing oxygen levels. A well-known commercially produced PEDOT-PSS(Poly(3,4-ethylene dioxythiophene) polystyrene sulfonate) polymer hole transfer layer was used to increase the oxygen gas sensor's sensitivity and detection range. This second device's performance was evaluated; this added layer could not improve the sensor performance. A new third device was designed; as a new layer over the zirconium-sensing layer, a third LiF layer was added. The third device was tested; polymer, zirconium, and LiF layered the third device and it worked efficiently in a lower oxygen level; furthermore, this design also improved the oxygen sensor detection range.

Dissolved oxygen (DO) level is of capital importance in the field of environmental monitoring, food fermentation, industrial production, and clinical medicine. Optical oxygen sensors with high sensitivity, accuracy, stability, and anti-jamming capability for DO content detection have provoked scientists’ attention in recent years. In this work, we selected platinum octaethylporphine (PtOEP), low-density polyethylene (LDPE), and high-density polyethylene (HDPE) as the fluorescent indicator and matrix materials, respectively. Porous LDPE/PtOEP and HDPE/PtOEP oxygen-sensing films were constructed by incorporating PtOEP in PE via the phase-separation method. The optimum parameters were obtained as follows: the concentrations of LDPE and HDPE solutions were 0.010 mg/L, and PtOEP was 8 μg. Based on the above study, the effects of different kinds of PE on the performance of the oxygen-sensing film were studied in detail, finding that the LDPE/PtOEP oxygen-sensing film had better photostability and could measure the DO concentrations of several water samples accurately.

A change in the content of energy substrates in myocardial mitochondria depending upon the vibration frequency and the duration of the total vertical vibration exposure was studied polarographically using a closed galvanic oxygen sensor (a Clark electrode) by comparing the endogenous respiration rates over a period when the homogenate was stored under aerobic conditions. After exposure to the longest vibration (56 sessions) with amplitude of 0.5 mm and frequency of 44 Hz, the rate of endogenous respiration after a 40-min incubation of myocardial tissue homogenate was 1.4 times slower (p < 0.05) than the control. This indicated the development of bottlenecking in the oxidation and utilization pathways of succinic acid, a decrease in the availability of endogenous substrates to the respiratory chain of cardiomyocytes mitochondria and, indirectly, mitochondrial-reticular network disruption and dysfunction.

In Ukraine today there are more than 6000 boiler plants with a heating capacity of up to 1 Gcal/h with an efficiency of about 70 %, requiring replacement or modernization, 40 % of boilers are operated with an efficiency of less than 82 %, about 11000 boilers with a capacity of 100 kW to 1 MW have been in operation for over 20 years. Although the part of these boilers in the municipal heat power system of Ukraine does not exceed 14 %, the projected savings in natural fuel in these boilers is more than 130 million cubic meters per year. Thus, increasing the efficiency of the fuel combustion process in small and medium power boilers is an urgent task at the present time. The article presents the results of creating a method and hardware that implements it, to increase the speed and reliability of monitoring the process of fuel combustion in boiler units based on measuring the concentration of residual oxygen in exhaust gases. The developed method is implemented by stepwise correction of the ratio of the air-fuel mixture entering to the furnace of the boiler for combustion, according to feedback signals from a broadband oxygen sensor manufactured by Bosch, located in the outgoing channel. The air-fuel ratio control with automatic adjustment of the blower fan speed depending on the amount of fossil fuel supplied for combustion ensures low-toxic combustion of fuel with low emissions of nitrogen oxides and carbon monoxide, and high efficiency. Additional use of a variable frequency drive in the combustion control system allows to reduce energy consumption by 30-40 %, eliminate starting currents and motor overloads, reduce mechanical wear of equipment, increase the service life of contact switching equipment. In general, the developed fuel combustion control system allows to optimize the fuel combustion mode, taking into account the actual conditions, operating modes of the boiler unit and fuel characteristics; to reduce specific fuel consumption by at least 10%; to reduce the level of emissions of nitrogen oxides up to 40 % and carbon monoxide up to 50 %; to increase the efficiency by at least 5 %; qualitatively to simplify the work of the boiler maintenance personnel.

High-temperature solid-state electrolyte is a key component of several important electrochemical devices, such as oxygen sensors for automobile exhaust control, solid oxide fuel cells (SOFCs) for power generation, and solid oxide electrolysis cells for H2 production from water electrolysis or CO2 electrochemical reduction to value-added chemicals. In particular, internal diffusion of protons or oxygen ions is a fundamental and crucial issue in the research of SOFCs, hypothetically based on either oxygen-ion-conducting electrolytes or proton-conducting electrolytes. Up to now, some electrolyte materials based on fluorite or perovskite structure were found to show certain degree of dual-ion transportation capability, while in available electrolyte database, particularly in the field of SOFCs, such dual-ion conductivity was seriously overlooked. Actually, few concerns arising to the simultaneous proton and oxygen-ion conductivities in electrolyte of SOFCs inevitably induce various inadequate and confusing results in literature. Understanding dual-ion transportation behavior in electrolyte is indisputably of great importance to explain some unusual fuel cell performance as reported in literature and enrich the knowledge of solid state ionics. On the other hand, exploration of novel dual-ion conducting electrolytes will benefit the development of SOFCs. In this review, we provide a comprehensive summary of the understanding of dual-ion transportation in solid electrolyte and recent advances of dual-ion conducting SOFCs. The oxygen ion and proton conduction mechanisms at elevated temperature inside oxide-based electrolyte materials are first introduced, and then (mixed) oxygen ion and proton conduction behaviors of fluorite and perovskite-type oxides are discussed. Following on, recent advances in the development of dual-ion conducting SOFCs based on fluorite and perovskite-type single-phase or composite electrolytes, are reviewed. Finally, the challenges in the development of dual-ion conducting SOFCs are discussed and future prospects are proposed.

In an oxygen consumption calorimeter system for measuring heat release rate, the CO/CO2 analyzer and the O2 analyzer for chemical species analysis of the sampling gas are the main factors that increase the construction cost of the system. In this experimental study, a low-cost device with performance similar to that of the existing high-cost device was developed. To evaluate the contribution of the CO/CO2 analyzer to the measurement of the heat release rate, the performance of unsteady and steady-state conditions depending on whether CO/CO2 was measured for diffusion flames with various fire growth rates was examined. As a result, it was confirmed that when only the O2 concentration was considered, the heat release rate could be measured accurately. Based on these results, the measurement performance of a low-cost O2 analyzer manufactured using an oxygen sensor for healthcare was verified. As a result of the verification of the low-cost O2 analyzer for diffusion flames with various fire growth rates, it was confirmed that the relative error was within 10% for unsteady and steady-state fire sources and can be used to measure the heat release rate.

A novel dense diffusion barrier material (YxSr1−xTi0.9In0.1O3−δ (x = 0.03, 0.05, 0.07)) was prepared by using a sol-gel method. The crystal structure, microstructures, electrical conductivity and ionic conductivity of barrier material were characterized. The results show that the samples exhibit the formation of cubic perovskite structure phase. The increase of Y-doping amount on A-site improved electrical conductivity and sinterability of materials. A limiting current oxygen sensor based on Y0.07Sr0.97Ti0.9In0.1O3−δ as a dense diffusion barrier shows excellent sensing performance. The linear relationship between limiting current logIL and 1000/T can described logIL = 4.6038 − 3.8475·1000/T. At 750 °C, 0.25% ≤ x(O2) ≤ 5.0%, the linear relationship between limiting current (IL) and oxygen amount (x(O2)) can described as IL = 7.0476 + 3.8751 x(O2).

Dye-based ultraviolet (UV) activated colorimetric oxygen indicator possess the potential for communication of package integrity to consumers. A research study was envisaged to evaluate the performance of biopolymer (sodium alginate, sodium caseinate and kappa-carrageenan) based ultraviolet activated smart oxygen sensor as spoilage or quality indicator for Mozzarella cheese. Mozzarella cheese samples were stored in a vacuum and 100% N2 at refrigerated temperature for 16 days and gas composition, indicator colour values and physico–chemical parameters (moisture, pH, acid degree value, thiobarbituric acid value and water activity) changes were studied. The indicators showed significant colour change after photo-activation and during storage also. The oxygen indicator’s colour was recovered at a very low oxygen concentration (0.381%). The indicator films could be potentially used for evaluating the purity of nitrogen and carbon dioxide gas cylinders used in modified atmosphere packaging of food.

We present the design of an optical fibre tip sensor for monitoring dissolved oxygen. It is based on the creation and modification of an all-fibre Fabry-Pérot interferometer, produced in a three-step process. First, fibre cavities are created in two fibres using a femtosecond laser that are then joined using arc fusion splicing, thereby forming a miniature fibre Fabry-Pérot interferometer. Finally, the femtosecond laser is used to create two symmetrical micro-holes exactly at the location of the Fabry-Pérot cavity and on opposite sides of the fibre, allowing liquids to access the cavity and perform refractive index sensing. For the dissolved oxygen sensing, the fibre sensor was first immersed in a hemoglobin solution to deposit a thin layer at the walls of the cavity to give oxygen discrimination. The sensitivity to the ratio of dissolved carbon dioxide to dissolved oxygen was demonstrated via the conversion of carboxyhemoglobin to oxyhemoglobin inside the cavity, thus changing the refractive index of the hemoglobin. The complete sensor was tested in two solutions with different oxygen concentrations and having the same refractive index and temperature. The first sample was a PBS solution dissolved in deionized water, which absorbs CO2 from the air after it is produced. The second sample was a PBS solution with sodium bicarbonate to ensure that all solution-state hemoglobin was converted to oxyhemoglobin, by converting the dissolved carbon dioxide into carbonate groups. We observed the difference between the two solutions that have the same refractive index and different oxygen levels by the means of a wavelength shift and amplitude change in the Fabry-Pérot interferometer spectrum due to the oxygenation of the hemoglobin.

There is a strong demand for reliable oxygen sensors in the fields of fitness tracking, health monitoring, and medical diagnostics. Recently, oxygen-sensing materials based on phosphorescence quenching by oxygen have attracted interest due to their high sensitivity, rapid response, and suitability for directly imaging oxygen distribution on large tissue areas. Here we tested different compositions of metalloporphyrins and their support matrices and identified optimal materials that can be applied to oxygen-sensing devices. Our results showed that a pivaloyl-terminated metalloporphyrin embedded in poly(propyl methacrylate) (PPMA) exhibits the highest porphyrin emission brightness and oxygen-dependent phosphorescence intensity changes can be easily visualized even by eye under ambient light. In vivo studies revealed that our PPMA-based, highly breathable oxygen-sensing films can be used to non-invasively detect changes in tissue oxygenation in a rabbit model, a promising step for integration into wearable devices. In addition, it was found that an alkyne-terminated metalloporphyrin embedded in tetraethyl orthosilicate (TEOS) shows the most rapid response time. The detailed composition exploration and material characterization described in this study provides a good resource towards developing more versatile oxygen-sensing devices.

Oxygen plays a key role in human physiology and is abnormally modulated in various disease pathologies making its in situ monitoring quite important. Most oxygen sensors are not able to measure oxygen levels deep inside the tissue or have mismatched electrode-tissue interfaces. In this study we developed a flexible thread-based oxygen sensor that combines the unique advantages of minimal invasiveness and superior flexibility offering the possibility for tissue integration. The sensor is featured by a simple and low-cost fabrication approach which allows for measuring the overall oxygen concentration either over a large surface area or locally at any spot in any three-dimensional environment with high spatial accuracy and high sensitivity. The sensor can sensitively detect dissolved oxygen levels within the physiological range of tissue oxygenation. The sensor's performance is insensitive to pH variation from 5.8 to 8.0. The sensor shows good repeatability and stability over a period of one week in phosphate buffered saline. In addition, the signal variation is less than 10% after hundreds of cycles of physical bending. Using a hydrogel-based tissue model the sensor has been shown to probe dissolved oxygen levels at different spatial locations inside a tissue-like environment.

Modification of boron-doped diamond (BDD) with gold-palladium nanoparticles (Au@PdNPs) was successfully performed. Prior to the modification, BDD was modified with allylamine to provide active sites for the attachment of nanoparticles, while the synthesis of Au@PdNPs was performed by chemical reduction of a palladium salt solution in a colloidal solution of gold nanoparticles. Characterization using TEM images showed that by controlling the palladium concentration, flower and core-shell shaped Au@PdNPs can be prepared. XPS studies confirmed that the nanoparticles with a flower shape could be attached better on the BDD surface. The Au@PdNPs-modified BDD (Au@PdNPs-BDD) electrodes were then examined for the oxygen reduction reaction in comparison with gold and palladium-based electrodes. One order higher current response was observed at Au@PdNPs-BDD compared to AuNPs-BDD, indicating the contribution of palladium in the oxygen reduction reaction. Good linearity with comparable limits of detection suggested that Au@PdNPs-BDD electrodes are promising for use as oxygen sensors. Furthermore, their application as BOD sensors was demonstrated.

The optical oxygen sensing capabilities of the porphyrin-based metal–organic frameworks, PCN-224, Pt(II)PCN-224 and Pd(II)PCN-224 were investigated. The bimolecular quenching constants (kq) of 37 000 (PCN-224), 6700 (Pd(II)PCN-224) and 3900 Pa−1 s−1 (Pt(II)PCN-224) were found and reveal an exceptionally high oxygen-permeability for these materials. Fast gas transport within the network, large pore sizes, and electronic and spatial isolation of the porphyrin indicator in the framework are held responsible for the unprecedentedly high kq values. PCN-224 shows 6.7 ns fluorescence lifetime and the fluorescence in air is quenched 4.2-fold. The metal–organic frameworks based on phosphorescent Pt(II) and Pd(II) porphyrins possess significantly longer decay times of 18.6 and 390 μs, respectively, and are suited to detect oxygen in trace and ultra-trace ranges with limits of detection of 1 and 0.015 Pa, respectively. Apart from free-standing crystals, also metal–organic frameworks supported on different fibrous substrates (poly(acrylonitrile) nanofibers, glass fibres), and flat substrates (TLC silica-gel, poly(amide) filter) were prepared in order to provide oxygen sensor materials of practical use. Electrospun and thermally treated poly(acrylonitrile) nanofibers were found to be particularly favourable and the resulting composite material exhibited the same sensitivity as the free crystals. All sensing materials show reversible cross-talk to humidity at levels up to 53% relative humidity but demonstrate a drastic decrease of oxygen sensitivity at high humidity levels and when exposed to water. A decrease of the quenching constant with rising temperature indicates an important role of surface-adsorbed oxygen in the quenching process.

The chemical oxygen surface exchange coefficient (kchem) values used to quantify and rank oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalyst performance for high-temperature, oxygen-exchange-enabled devices (such as Solid Oxide Fuel Cells, Solid Oxide Electrolysis Cells, oxygen sensors, etc.) are often determined electrically, with the aid of precious metal current collectors. However, the curvature relaxation (κR) and Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) analyses performed here on Pulsed Laser Deposited thin films of the oxygen exchange catalyst Pr0.1Ce0.9O2−x (PCO) show that unpolarized platinum current collectors dramatically improve the kchem of Si-contaminated PCO by reducing the Si concentration at the PCO surface and/or diffusing into the PCO; even for PCO thin films only exposed to mild temperatures of 500 °C. This suggests that precious metal current collectors are likely responsible for some of the large kchem variation reported in the literature for “identical” materials tested under “identical” conditions.

In this study, an efficient on-site marine oil spillage monitoring probe was developed by fixing oxygen consumption sensors into hydrophobic/oleophilic oil-absorbing porous materials. The impact of thickness and characters of the porous materials, the types of spilled oil, and the presence of salts and vibration in water on the parameters of the obtained signals was investigated. The probe could be used to detect the various representative types of spilled oils including lubricating oil, corn oil, soybean oil, n-hexane, petroleum ether and toluene, even in simulated sea water vibrating at different levels, having over 33 times reduced reliable low detection limit (RLDL) in detecting soybean oil in water (from 36.5 g L−1 to 1.1 g L−1). The response time and signal-to-noise ratios (SNRs) of the probe varied greatly with the dynamic absorbing speed and oxygen barrier property of the spilled oils in the porous material, respectively. The probe showing the highest SNR of 190 dB for a 50 g L−1 on-site soybean oil spillage and the fastest response time of 9 s for a 50 g L−1 on-site toluene spillage in water may potentially be used as a key component in near-shore marine oil spillage monitoring systems to provide early-stage pollution warning.

A-site-deficient Y, Cr doubly doped SrTiO3 ((Y0.08Sr0.92)1-xTi0.8Cr0.2O3−δ (x = 0.01, 0.03, 0.05)) powders were synthesized via sol–gel method, followed by sintering at 1450 °C at ambient condition. The phase composition, mixed conductivities, and sensing performance are characterized to identify the influence of A-site deficiency on the Y- and Cr-doubly doped SrTiO3. The ionic conductivity and total conductivity of (Y0.08Sr0.92)1-xTi0.8Cr0.2O3−δ clearly increase and decrease upon an increase in the A-site deficiency, respectively. The enlarged saddle point and decreased relaxation time are responsible for the augmentation of ionic conductivity. The oxygen sensor with (Y0.08Sr0.92)1-xTi0.8Cr0.2O3−δ dense diffusion layer show superior sensing performance with A-site deficiency level increasing. The relationship between logIL and 1000/T is obtained and the charge compensation mechanism is systematically discussed. The obtained results demonstrated that limiting current is nearly independent of temperature at high operating temperature. This paper provides a chemical strategy to enhance the mixed conductivity of oxygen sensors through Y- and Cr-double doping and via a simple, low cost, and traditional sol–gel technique.

The use of optical sensors for oxygen measurement is becoming more important because of their capability for low-cost and direct measurement, but as yet, little has been reported about their long-term performance. Phosphorescent sensors based on platinum octaethylporphyrin (PtOEP) embedded in polymer matrices tend to degrade with time. To reduce the rate of degradation, sensor films were fabricated and then coated with a layer of polydimethylsiloxane (PDMS) and tested in a six-month study. The PDMS-coated sensors showed an average degradation rate of ~0.073 %/day, compared to ~0.18 %/day for uncoated sensors. Titania beads were also incorporated into the films to increase light scattering and improve the response; these beads compensated to some degree for the absorption due to the PDMS films. The films with titania beads improved the response significantly (about 40%) compared to the films without titania beads. Incorporation of titania beads also moderately improved the aging characteristics.

Sediment oxygen demand (SOD) measurement currently requires a long preparation time and bulky experimental equipment, which represent major obstacles to conducting SOD measurements. We developed a new SOD measurement method that can be easily conducted in a shorter time than the existing laboratory method. The undisturbed sediment core was transferred into the custom-made small glass vial (inner diameter 12.8 mm, length 125 mm). The SOD sample was incubated in the dark with or without stirring the overlying water inside the vial. The change in DO concentration was measured using a non-contact fluorescent oxygen sensor, and then the SOD was calculated. For comparison and verification of the new method, SOD was also measured using a large undisturbed sediment core (inner diameter 11 cm, length 50 cm). The SOD measurements using the new method were positively correlated with the SOD measurements using the large undisturbed sediment core, suggesting that the new method is a feasible alternative to the conventional method. In the new method, many SOD measurements can be taken from a single sediment core sample. This makes it possible to reduce the uncertainty associated with the highly heterogeneous structure of the sediments, and thus the new method has great advantages in obtaining reliable SOD data. A novel high-throughput method for SOD was developed that shortens sample preparation time and improves convenience of measurement. The new method is expected to contribute substantially to the accumulation of SOD monitoring data and to make great progress in elucidating the dynamics of dissolved oxygen in lakes.

The composites Pt3Ni/C and Pt3Co/C are electrocatalysts for oxygen reduction reactions (ORRs). This study compares the electrocatalytic activity of these electrodes that are used to detect oxygen, and determines their suitability for use in proton exchange membrane fuel cells (PEMFCs). Chemical reduction is used to produce the Pt3Ni/C and Pt3Co/C electrocatalysts. The particle size, elemental composition and crystallinity of the intermetallic electrocatalysts are determined using transmission electron microscopy (TEM) and an energy-dispersive spectrometer (EDX). The ORR activity of the Pt3Ni/C and Pt3Co/C electrocatalysts is determined using cyclic voltammetry (CV), a polarization curve (PC) and a rotating disk electrode (RDE). The Pt3Ni/C electrode registers a greater current for the ORR as compared to the Pt3Co/C electrode. Both electrodes exhibit a linear relationship between response current and oxygen concentration in the detection range from 100 to 1000 ppm. The Pt3Ni/C electrode exhibits a significant sensitivity to oxygen up to 13.4 μA ppm−1 cm−2. A membrane electrode assembly (MEA) that is produced using Pt3Ni/C as a cathodic electrocatalyst in a single PEMFC generates a maximum power density of 1097 mW cm−2.

Oxygen consumption (OC) for the combustion of dried sewage sludge was determined by an equipped YSZ oxygen sensor. Probably due to the good combustion of the sludge, it was not affected by the temp...

We exploit a high-performing resistive-type trace oxygen sensor based on 2D high-mobility semiconducting Bi2 O2 Se nanoplates. Scanning tunneling microscopy combined with first-principle calculations confirms an amorphous Se atomic layer formed on the surface of 2D Bi2 O2 Se exposed to oxygen, which contributes to larger specific surface area and abundant active adsorption sites. Such 2D Bi2 O2 Se oxygen sensors have remarkable oxygen-adsorption induced variations of carrier density/mobility, and exhibit an ultrahigh sensitivity featuring minimum detection limit of 0.25 ppm, long-term stability, high durativity, and wide-range response to concentration up to 400 ppm at room temperature. 2D Bi2 O2 Se arrayed sensors integrated in parallel form are found to possess an oxygen detection minimum of sub-0.25 ppm ascribed to an enhanced signal-to-noise ratio. These advanced sensor characteristics involving ease integration show 2D Bi2 O2 Se is an ideal candidate for trace oxygen detection.

Fast response rate is a desirable character of gas sensors to monitor kinds of environments. In order to improve the response and recovery rate of YSZ-based electrochemical oxygen sensors, the laser ablation method was used to modify surface of YSZ substrates, and the effect of triple phase boundary (TPB) was studied. Results have shown that the increment of the TPB density can substantially improve the response rate, especially at a relative low working temperature (500 °C), and the max increment that is 70% was realized. Meanwhile, the sensor exhibited good selectivity toward interferences of reducing gases at this relative low working temperature. The results had provided a convenient and steerable way to improve the response, recovery rate, and electrochemical catalytic activity of YSZ-based electrochemical devices at medium and low working temperature.

Detection of oxygen plays an important role in food industry, medicine and controlling automotive exhaust. Here, we have developed a Co3O4 nanoparticle-based oxygen gas sensor. Effect of Gadolinium (Gd) doping on oxygen sensing is investigated using the variation in electrical resistance method which clearly reveals improvement in the sensitivity with the increase in Gadolinium doping in Co3O4. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) studies were systematically performed, to understand the effect of the morphology and crystallographic phase on the level of sensitivity with Gadolinium doping. XRD studies reveal a distortion in the Co3O4 lattice as the lattice parameters increase with increasing Gd doping. SEM and TEM show a change in particle shape and size with Gd doping. Presence of both Co+2 and Co+3 oxidation states were confirmed by XPS. Gd doping, up to 6%, improved the gas sensing response of Co3O4 nanoparticles which is attributed to the decrease in particle size and an increase in oxygen adsorption with Gd doping. Minimum response time of 4 s, 6 s, 10 s and 14 s were observed for pure Co3O4 in 1%, 2%, 3% and 4% oxygen environment respectively. Pure Co3O4 nanoparticles also showed minimum recovery time which was 6 s, 7 s, 9 s and 11 s in 1%, 2%, 3% and 4% oxygen environment respectively. All the prepared compositions were selective to oxygen at 240 °C.

Irrespective of the change in kind of energy to renewables there are many processes in which combustion of conventional fuels and biofuel are necessary. For cement and glass production, paper fabrication and air traffic it is absolutely essential to control the combustion processes by intelligent sensors in order to maximize the efficiency and to minimize the emission of harmful substances such as NOx and CO. Mainly oxygen sensors based on solid electrolytes and calorimetric sensors using the heat formation by catalytic combustion of CO and hydrocarbons with two resistance temperature detectors (RTD) are utilized. Recently, tunable diode laser spectroscopy (TDLS) became attractive in chemical plants. Several analytical companies are offering in-situ or extractive laser analyzers for combustion gases.

During the operation of internal combustion engines the air-fuel ratio (A/F) is an important parameter which affects fuel consumption and pollutant emissions. The automotive oxygen sensor (Lambda) measures the quantity of residual oxygen in the combustion gases. Sensor degradation in time due to the exposure to high temperatures causes a distortion in controlling the A/F with the increase in gas emissions. In this paper an experimental stand is designed to test oxygen sensor degradation in laboratory condition. Four oxygen sensors were tested function of temperature and time recording their variation in resistance and voltage. The results showed similar values in the curves for all sensors tested.

Indirect calorimetry (IC) is considered the gold standard for measuring resting energy expenditure (REE). This review presents an overview of the different techniques to assess REE with special regard to the use of IC in critically ill patients on extracorporeal membrane oxygenation (ECMO), as well as to the sensors used in commercially available indirect calorimeters. The theoretical and technical aspects of IC in spontaneously breathing subjects and critically ill patients on mechanical ventilation and/or ECMO are covered and a critical review and comparison of the different techniques and sensors is provided. This review also aims to accurately present the physical quantities and mathematical concepts regarding IC to reduce errors and promote consistency in further research. By studying IC on ECMO from an engineering point of view rather than a medical point of view, new problem definitions come into play to further advance these techniques.

In this communication, we propose a new strategy and present the dual pH/O2 lifetime sensor based on covalent conjugation of fluorescein (pH sensor) and orthometalated iridium complex (O2 sensor) to human serum albumin (HSA). The resulting conjugate demonstrates biocompatibility, low toxicity, fast cellular uptake, and displays independent lifetime responses onto variations in media acidity and oxygen concentration that makes it suitable for application as effective pH/O2 probe in luminescent microscopy by using FLIM/PLIM detection mode. The concept applicability has been exemplified by dual spatially and temporally localized intracellular sensing of pH and O2 concentration in living cells.

A highly sensitive, biocompatible, and scalable phosphorescent oxygen sensor formulation is designed and evaluated for use in continuous metabolite sensors for biological systems. Ethyl cellulose (EC) and polystyrene (PS) nanoparticles (NPs) stabilized with Pluronic F68 (PF 68), Polydimethylsiloxane-b-polyethyleneglycol methyl ether (PDMS-PEG), sodium dodecylsulfate (SDS), and cetyltimethylammonium bromide (CTAB) were prepared and studied. The resulting NPs with eight different surfactant–polymer matrix combinations were evaluated for physical properties, oxygen sensitivity, effect of changes in dispersion matrix, and cytotoxicity. The EC NPs exhibited a narrower size distribution and 40% higher sensitivity than PS, with Stern–Volmer constants (Ksv) 0.041–0.052 µM−1 for EC, compared to 0.029–0.034 µM−1 for PS. Notably, ethyl cellulose NPs protected with PF68 were selected as the preferred formulation, as they were not cytotoxic towards 3T3 fibroblasts and exhibited a wide phosphorescence lifetime response of >211.1 µs over 258–0 µM and ~100 µs over 2.58–0 µM oxygen, with a limit of detection (LoD) of oxygen in aqueous phase of 0.0016 µM. The EC-PF68 NPs were then efficiently encapsulated in alginate microparticles along with glucose oxidase (GOx) and catalase (CAT) to form phosphorescent nanoparticles-in-microparticle (NIMs) glucose sensing microdomains. The fabricated glucose sensors showed a sensitivity of 0.40 µs dL mg−1 with a dynamic phosphorescence lifetime range of 46.6–197.1 µs over 0–150 mg dL−1 glucose, with a glucose LoD of 18.3 mg dL−1 and maximum distinguishable concentration of 111.1 mg dL−1. Similarly, lactate sensors were prepared with NIMs microdomains containing lactate oxidase (LOx) and found to have a detection range of 0–14 mg dL−1 with LoD of 1.8 mg dL−1 and maximum concentration of 13.7 mg dL−1 with lactate sensitivity of 10.7 µs dL mg−1. Owing to its versatility, the proposed NIMs-based design can be extended to a wide range of metabolites and different oxygen-sensing dyes with different excitation wavelengths based on specific application.

Previous studies have shown that the pollutants in exhaust gas can cause performance deterioration in air-fuel oxygen sensors. Although the content of Pb in fuel oil is as low as 5 mg/L, the effect of long-term Pb accumulation on TiO2 oxygen sensors is still unclear. In this paper, the influence mechanism of Pb-containing additives in automobile exhaust gas on the response characteristics of TiO2 oxygen sensors was simulated and studied by depositing Pb-containing pollutants on the surface of a TiO2 sensitive film. It was found that the accumulation of Pb changed the surface gas adsorption state and reduced the activation energy of TiO2, thus affecting the steady-state response voltage and response speed of the TiO2-based oxygen sensor.

The optical oxygen sensing capabilities of the porphyrin-based metal-organic frameworks, PCN-224, Pt(II)PCN-224 and Pd(II)PCN-224 were investigated. The bimolecular quenching constants (kq) of 37000 (PCN-224), 6700 (Pd(II)PCN-224) and 3900 Pa-1s-1 (Pt(II)PCN-224) were found and reveal an exceptionally high oxygen-permeability for these materials. A fast gas transport within the network, large pore sizes, electronic and spatial isolation of the porphyrin indicator in the framework are held responsible for the unprecedentedly high kq values. PCN-224 shows 6.7 ns fluorescence lifetime and the fluorescence in air is quenched by 4.2-fold. The metal-organic frameworks based on phosphorescent Pt(II) and Pd(II) porphyrins possess significantly longer decay times of 18.6 and 390 µs, respectively, and are suited to detect oxygen in trace and ultra-trace ranges with limits of detection of 1 and 0.015 Pa, respectively. Apart from free-standing crystals, also metal-organic frameworks supported on different fibrous substrates (poly(acrylonitrile) nanofibers, glass fibres), and flat substrates (TLC silica-gel, poly(amide) filter) were prepared in order to provide oxygen sensor materials of practical use. Electrospun and thermally treated poly(acrylonitrile) nanofibers were proven to be particularly favourable and the resulting composite material exhibited the same sensitivity as the free crystals. All sensing materials show reversible cross-talk to humidity at levels up to 53 % relative humidity but demonstrate a drastic decrease of oxygen sensitivity at high humidity levels and when exposed to water.

In vitro determination of the hemoglobin oxygen dissociation curve (ODC) requires highly elaborate, specialized, and costly technical equipment. In addition, there is a lack of methods that combine reliable ODC recordings with high throughput in small blood samples for routine analysis. We here introduce a modified, commercial 96‐well plate with an integrated unidirectional gas flow system specifically adapted for use in fluorescence microplate readers. Up to 92 samples of whole or hemolyzed, buffered or unbuffered blood, including appropriate controls or internal standard hemoglobin solutions, can be analyzed within ~25 min. Oxygen saturation is measured in each well with dual wavelength spectroscopy, and oxygen partial pressure using fluorescence lifetime of commercial oxygen sensors at the in‐ and outlet ports of the gas‐flow system. Precision and accuracy of this method have been determined and were compared with those of a standard method. We further present two applications that exemplarily highlight the usefulness and impact of this novel approach for clinical diagnostics or basic research., Hemoglobin oxygen dissociation curves are measured using a modified, commercial 96‐well plate with an integrated unidirectional gas‐flow system specifically adapted for use in fluorescence microplate readers. Up to 92 samples of whole or hemolyzed, buffered or unbuffered blood, including appropriate controls or internal standard hemoglobin solutions, can be analyzed within ~25 min.

Nanopowders and thin films of (СeO2)1-x(Y2O3)x composition (x = 0.10, 0.15 and 0.20) were obtained by the sol-gel process, using hydrolytically active complexes of the metal alkoxoacetylacetonate class [M(C5H7O2)3-y(C5H11Oi)y] (M = Ce3+ and Y3+) as precursors. The impact of the chemical composition and crystallization conditions on the microstructure, electrophysical and chemosensory characteristics of the obtained planar-type solid electrolytes was studied. The prospects of the thin-film nanostructures obtained as receptor components of resistive oxygen sensors, as well as of electrolytes of planar-type intermediate-temperature solid oxide fuel cells (SOFC) have been shown. It has been found that (CeO2)0.90(Y2O3)0.10 thin films demonstrate the maximum values of electrical conductivity (550 °C) and the highest sensory response when detecting oxygen (concentration range 1–20%, operating temperature range 300–450 °C).

First-principles calculations were used to explore the effect of various Y-doping levels on the electrical conductivity of SrTiO3. Herein, we prepared ((Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ)/x/3Co3O4 (x = 0.1, 0.2, 0.3)) composites using a solid state reaction method. The properties of these sensing materials and the fabricated sensors including crystal phase composition, microstructures, oxygen ionic conductivity, total conductivity and sensor performance were investigated in detail. XRD demonstrates the formation of a highly cubic perovskite structure. The introduction of Co3O4 promotes remarkably the electronic conductivity of the Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ/x/3Co3O4 composites due to the formation of n-type CoO and p-type Co2O3. A limiting current oxygen sensor based on (Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ)/x/3Co3O4 as a dense diffusion barrier shows excellent sensing performance. The recovery time is less than the response time, indicating that Co2O3 promotes the gas desorption reaction which results in a shorter recovery time. The obtained results demonstrate a direct relationship between limiting current (IL) and oxygen content.

Oxygen measurement and control system is critical for minimizing corrosion in nuclear systems. Oxygen measurement and control tools use lead-bismuth eutectic (LBE) and pure lead as a coolant or as ...

A comprehensive overview is provided about the role of bulk conductivity contributions in compounds of the composition YbxCa1-xMnO3 (0–10 at. % Yb-dopant concentration). For this purpose, in-situ impedance spectroscopy was successfully employed at different temperatures (−100 up to 300 °C) and frequencies (1 Hz–1 MHz). These experiments reveal the main role of grain boundaries as well as electronic and ionic contributions in conductivity. The contribution of different resistance components in electric transport properties were proposed on the base of a double-Schottky-barrier model. Migration of oxygen vacancies and their participation in conductivity were studied and the results are confirmed by observing oxygen released using a ZrO2 oxygen sensor during dilatometry measurements in a wide range of temperatures.

Multisensor detectors have merits of low cost, compact size, and capability of supplying accurate and reliable information otherwise hard to obtain by any single sensors. They are therefore highly desired in various applications. Despite the advantages and needs, they face great challenges in technique especially when integrating sensors with different sensing principles. To bridge the gap between the demand and technique, we here demonstrated an integration of electrochemical and colorimetric sensors with a webcam readout for multiple gas detection. Designed with two parallel gas channels but independent sensor cells, the dual-sensor detector could simultaneously detect each gas from their gas mixture by analysis of the group photo of the two sensors. Using Ag electro-dissolution as reporter, the bipolar electrochemical sensor achieved quantitative analysis for the first time thanks to application of pulse voltage. The sacrificed Ag layer used in the bipolar electrochemical (EC) sensor was recycled from CD, which further decreased the sensor cost and supplied a new way of CD recycling. The EC O2 sensor response, edge displacement of Ag layer due to electrochemical dissolution, has a linear relationship with O2 concentration ranging from 0 to 30% and has good selectivity to common oxidative gases. The colorimetric NO2 sensor linearly responded to NO2 concentrations ranging from 0 to 230 ppb with low detection limit of 10 ppb, good selectivity, and humidity tolerance. This integration method could be extended to integrating other gas sensors.