Control over molecular oxygen concentrations in cell cultures is vital for maintaining normal physiological functions and modelling pathological conditions. However, current approaches for measuring oxygen are often invasive or limited in their capability to assess oxygen distribution in large-volume 3D cell cultures beyond a few hundred microns in depth. In this work, we have developed an adaptable method utilizing multifocal optical projection microscopy and commercially available fluorescent microsensor beads. Fluorescent projection images of the beads were acquired while simultaneously measuring oxygen concentration with an optical fibre-based sensor. A Stern-Volmer calibration curve was then generated by depleting oxygen with sodium sulfite, allowing fluorescence intensity to be converted into oxygen concentration. The method was demonstrated to quantify oxygen concentrations at depths beyond typical 3D cell culture dimensions, up to 21 mm. Fibroblasts were cultured within agarose hydrogels at varying cell densities (200 000 to 700 000 cells per ml). The results revealed a significant decrease in oxygen concentration with increasing cell density and depth of the specimen, thus also highlighting the need for O2 measurements in 3D cell cultures. Here we demonstrated that our method is well suited for minimally invasive quantification of oxygen levels and gradients, especially in large-volume hydrogel-based 3D cell cultures.

Abstract To meet the demand for real-time oxygen concentration monitoring in flight tests of aircraft fuel tank inerting systems, this paper reviews three mainstream airborne oxygen concentration measurement technologies: the electrochemical method, TDLAS, and the fluorescence quenching method. It also elaborates on their working principles and technical characteristics. Accuracy verification tests were carried out on typical existing domestic testing equipment. Their measurement performance under different pressure conditions was then compared and analyzed. The results show that the measurement accuracy of all three types of equipment can reach within ±0.3% under normal pressure, while the equipment based on TDLAS and fluorescence quenching principles performs better in low-pressure environments. Furthermore, considering the application scenarios of flight tests, the equipment performance was comprehensively evaluated from multiple aspects. The advantages and disadvantages of each type of system were summarized, and improvement directions, such as modular design and gas path protection optimization, were proposed. The research results can provide technical support and serve as a reference for the subsequent development of airborne oxygen concentration monitoring systems.

Precise control and measurement of the cellular microenvironment, particularly oxygen concentration, are crucial for developing physiologically relevant in vitro models. However, current methods often lack the spatial resolution and throughput needed to investigate complex, oxygen-dependent biological mechanisms in 3D cell cultures. Here, we present an advanced platform based on microcavity arrays featuring integrated, ratiometric oxygen sensors, so-called SensoSpheres. A unique bevel design at the cavity entrance enables the non-invasive, real-time measurement of pericellular oxygen concentration and oxygen gradients. We established protocols for generating spheroids from various cell lines (e.g., HepG2, HeLa) and characterized their metabolic responses under precisely controlled hypoxic, normoxic, and hyperoxic conditions. Using a dose–response assay, we demonstrate the platform’s sensitivity in capturing distinct metabolic shifts in response to acetaminophen and cisplatin. Furthermore, we introduce the Oxygen Consumption Recovery Rate (OCRR) as a novel parameter to quantify cellular resilience after exposure to toxic compounds such as cisplatin and acetaminophen. This high-throughput-compatible platform represents a significant methodological advancement, enabling detailed studies of oxygen-dependent cellular processes, drug toxicity, and metabolic adaptation. Its potential for integration into microfluidic systems paves the way for more sophisticated organ-on-chip models, ultimately improving the predictive power of preclinical research.

Sulfur, despite its minor presence (∼ 250 µg.g −1 ) in the bulk silicate Earth, can exhibit high solubility in melts, up to 1.5 wt. %, depending on the melt’s oxidation state. Sulfur is also integral to the formation of economically significant metal ores. This study reports high-temperature equilibrium sulfur isotope fractionation between melt, sulfide, and gas phases using a dynamic 1-atm gas-mixing furnace. Equilibrium experiments conducted on a basaltic system at temperatures of 1200, 1300, and 1400 °C indicate that equilibrium sulfur isotope fractionation between a sulfide liquid and SO 2 gas is a linear function of oxygen concentration in the sulfide phase. The fractionation factor is expected to be close to 0 ‰, for a pure FeS sulfide liquid. The experiments also reveal an isotopic fractionation of S from – 0.49 ± 0.97 up to + 5.30 ± 0.59 ‰ between the silicate melt and sulfide liquid, with the silicate melt being enriched in 34 S. This variation was best modelled by combining compositional elements of sulfide liquid (oxygen and sulfur) and silicate melt (MgO and Na 2 O). Our results show a new mechanism of sulfur isotope fractionation between silicate melt and sulfide liquid that results in isotopically heavier melts without sulfate due to the presence of oxygen in the sulfide liquid. Applying our model to Mid-Oceanic Ridge Basalts (MORBs) shows zero S isotope fractionation is expected when the composition of the sulfide liquid is between Fe 0.92 S and Fe 0.86 SO 0.05 . This study shows that measurements of oxygen concentration in natural sulfides are required to accurately interpret sulfur isotope compositions during magma evolution.

The current trend in the development of Proton Exchange Membrane Fuel Cells (PEMFCs) towards high-power (>300 kW) applications is driving manufacturers to adopt ever-larger electrodes in pursuit of improvements in power density and durability required for heavy-duty use cases. One of the most significant challenges in large-format cells is maintaining a uniform oxygen concentration at the cathode. There are currently no direct techniques for measurement of the oxygen concentration at the interface between the cathode catalyst layer (CL) and membrane, where starvation is most likely to occur. In this work, a novel ‘instrumented membrane’ approach has been developed to address this gap in diagnostic capability. An in-situ , chronoamperometric oxygen sensor is fabricated directly on the PEMFC membrane. A data-driven model taking sensor DC current and impedance as inputs is able to predict local oxygen concentration at the PEM/catalyst layer interface with an accuracy of ±5 %. This in-situ diagnostic approach is demonstrated as a powerful tool for measuring and evaluating the distribution of oxygen in large-format PEMFCs, offering deep insights enabling improvements in system longevity and performance. • Innovative in-situ O 2 concentration sensor for large-format PEMFCs developed. • Data-driven model uses impedance and DC current to predict O 2 concentration. • O 2 concentration prediction offers insight into PEMFC performance and durability.

In this paper, an improved methodology for modeling and measurement of net heat loss from the combustion process, along with a case study demonstrating its enhancement, has been developed and experimentally validated. The methodology begins with the modeling and measurement of combustion efficiency, utilizing lambda sensor measurements of oxygen concentration during intake, in-cylinder, residual gas fraction (RGF), and exhaust processes. Subsequently, based on the combustion efficiency measurements and the principles of energy conservation, net heat loss from the cylinder walls, crevices, and lubricant oil is calculated. Experimental results indicate that heat loss reaches a reasonable level near stoichiometric conditions across the full range of operating conditions tested, validating findings from other research. As part of the case study, a combustion phase control strategy (CA50) aimed at reducing heat loss has been developed and experimentally validated. The results demonstrate that net heat loss can be effectively reduced while simultaneously improving thermal efficiency in leaner zones through combustion phase control. Furthermore, the validation process included assessing improved combustion efficiency across various gasoline properties and calibrating data against existing literature, which confirmed consistent trends and magnitudes in the transition from rich to lean zones. Finally, experimental validation was conducted on a full-scale gasoline engine test bench to showcase the effectiveness of the proposed models for combustion efficiency and net heat loss, along with their improvements.

Bubble-mediated gas exchange associated with wave breaking is a critical pathway for ocean-atmosphere exchange of low solubility gases such as oxygen. Yet, ocean and climate models, as well as observation-based products, usually rely on wind-only air-sea flux formulations derived from carbon constraints that ignore the asymmetric nature of the bubble flux, contributing to discrepancies between estimates of oxygen inventories and their response to climate change. Without bubbles, gas exchange is controlled by a symmetric wind-driven exchange, with the ocean-atmosphere gas partial pressure difference controlling whether outgassing or uptake occurs. Bubbles entrained by wave breaking can enhance this symmetric turbulent exchange, and contribute an additional asymmetric flux, always leading to an uptake, as they get squeezed by hydrostatic pressure (large bubbles) or collapse and fully dissolve (small bubbles). We present an observation-constrained theoretical framework of the air-sea flux accounting for air entrainment due to wave breaking and symmetric and asymmetric bubble exchange. The combined evidence from theory, laboratory, and field measurements of carbon dioxide fluxes, oxygen concentration, and noble gas supersaturation yields a universal formulation of gas exchange which we implement into a global ocean biogeochemical model. We discuss the resulting oxygen fluxes and demonstrate that our wind-wave-bubble formulation better reproduces observed in situ oxygen concentrations in water mass formation regions, where air-sea exchange is high, than a commonly used wind-only formulation. We show that the asymmetric bubble flux is essential for evaluating air-sea oxygen fluxes and estimating the magnitude of the ocean oxygen loss associated with global warming.

To enhance the automated control of the plugging meter (PM) and thereby enhance detection fidelity in ultralow oxygen environments [ ≤ 1 parts per million by weight (wppm)], a novel proportional derivative controller has been implemented with conventional PM hardware. This ramp sign stabilized flow (RSSF) controller manipulates the sign (heating or cooling direction) at a fixed rate, enabling precise temperature adjustment around the saturation temperature of the bulk sodium. This adjustment helps maintain flow stability in a partially formed sodium oxide plug, thus greatly reducing the temperature amplitude in the plugging cycle and promoting simple and accurate oxygen determinations in addition to an increased sampling rate. Rather than relying on the subjective nature of indexing the time when the flow rate changes due to the plugging or unplugging onset to the PM temperature, a running average of the correlated oxygen concentration with time over multiple plugging events can provide oxygen readings ranging from an absolute uncertainty of 500 wppb in real time to less than 50 wppb for a 24-h sampling window. The RSSF controller was tested at 508 ± 7 wppb with measured oxygen of 542 ± 179 wppb, further reducing the variance between the saturation temperature and the plugging temperature.

BackgroundMinibeam radiotherapy has demonstrated its potential to reduce normal tissue toxicity while maintaining tumor control. However, the underlying mechanisms behind this phenomenon remain unknown. Recent theoretical studies suggest a dose surrogate by diffusion of H2O2 into the valley regions.PurposeThe aim of this study is to experimentally investigate oxygen depletion and diffusion upon minibeam (MB) irradiation.MethodsA 3D‐printed water phantom with four sensors was developed to enable the real‐time, simultaneous measurement of oxygen concentration in the peak and valley. Water with 0%–11% O2 and 0.1%/5.0% CO2 was irradiated with broad beam (BB) and MB characterized by peak and valley widths of 2 mm × 2 mm and 0.5 mm × 2 mm. The depletion was further compared in other chemical environments.ResultsThe oxygen depletion rates per dose in hypoxic water in the valley regions were found to be 3–7 times higher compared to the peaks or BB. This observation was found to be independent of oxygen concentration above 2 %, indicating oxygen depletion saturation. For MB, diffusion between peaks and valleys was observed. After a certain period, an equilibrium between diffusion and dose rate differences was established. Glutathione and HEPES as a medium increased the depletion further and distinguished MB from BB.ConclusionsA novel way of simultaneously measuring oxygen in the peak and valley of the MB dose pattern was introduced. The observed oxygen depletion saturation and diffusion between the peaks and valleys suggest the importance of oxygen in spatially fractionated radiotherapy studies, which is even greater for 5 mM glutathione compared to water.

Flow Analyzer allows measurement of flow, pressure, volume, and oxygen concentration delivered to the patient, with PEEP (Positive End Expiratory Pressure) being a crucial parameter in mechanical ventilation. Incorrect PEEP values can elevate the risk of patient mortality. The recommended PEEP range is 5-24 cmH2O, and administration is determined by the patient's clinical condition. This research aims to identify stable and highly accurate pressure sensors by comparing the MPX2010DP and MPX5010DP sensors with pressure readings from a Digital Pressure Meter (DPM). The study involves 5 repetitions of a lung test, each with 11 pressure reading points, within a pressure measurement range of 0-30 cmH2O. The DPM has a resolution of 1 cmH2O, while both pressure sensors have a resolution of 0.01 cmH2O. Results indicated that the MPX2010DP sensor has the smallest error percentage, specifically 0.00%, at a pressure increase of 5 cmH2O and 20 cmH2O. Conversely, the MPX2010DP sensor shows the largest error percentage, 5.16%, when the pressure decreases by 5 cmH2O. The highest standard deviation of 0.52 is observed in the MPX5010DP sensor at a 20 cmH2O pressure increase, while the maximum correction value of 0.54 is found in the MPX5010DP sensor at a 25 cmH2O pressure increase. According to the ANOVA test, there is no significant difference in pressure produced between the MPX2010DP sensor, MPX5010DP sensor, and DPM. The sensors are well-calibrated and provide accurate readings according to calibration tool standards. Therefore, the MPX2010DP and MPX5010DP sensors are deemed accurate for measuring PEEP parameters in ventilators. Based on the obtained data, it can be concluded that the MPX2010DP sensor is more accurate and stable.

Temperature and relative oxygen concentration fields were measured in an optically accessible solid fuel ramjet combustor using coherent anti-Stokes Raman scattering (CARS). Additionally, planar laser-induced fluorescence measurements of the hydroxyl radical (OH-PLIF) were performed to spatially characterize flame structure. The experiment was operated with an inlet air temperature of 670 K, mass flow rate of 1.14 kg/s, and pressure of 0.57 MPa. The dual-pump CARS system provided simultaneous measurements of the nitrogen Q-branch ro-vibrational energy level structure of nitrogen and pure-rotational energy level structure of nitrogen and oxygen. These spectra possess ample features for comparison to theory at temperatures of 600–2500 K. Comparison between CARS and OH-PLIF measurements indicated that the highest temperature and highest OH-PLIF intensity are located within the downstream extent of the recirculation zone. A comparison of wall-normal profiles of the OH-PLIF and CARS measurements indicates that maximum temperature standard deviation matches the mean location of flame heat release, while the maximum temperature better correlates with the OH-PLIF intensity. A bulk transport of hot combustion products toward the wall is observed in the instantaneous OH-PLIF images. This phenomenon is critical for the energy transfer to the grain that supports the local fuel regression to support the diffusion flame.

Optical oxygen sensors have attracted considerable attention owing to their high sensitivity, rapid response, and broad applicability. However, their test results may be affected by fluctuations in the pump light source and instability of the detection equipment. In this study, the intrinsic luminescence of pine wood was utilized as the reference signal, and the luminescence of platinum(II) octaethylporphyrin (PtOEP) was employed as the oxygen indication signal, to fabricate a dual-signal ratiometric oxygen sensor PtOEP/PDMS@Pine. The ratio of the luminescence of pine wood to that of PtOEP was defined as the optical parameter (OP). OP increased linearly with oxygen concentration ([O2]) in the range of 10–100 kPa, and a calibration curve was obtained. The sensor exhibits excellent anti-interference capabilities, effectively resisting fluctuations from laser sources and detection equipment. It also displays stable hydrophobicity with a contact angle of 118.3° and maintains excellent photostability under continuous illumination. The sensor exhibited long-term stability within 90 days and robust recovery performance during cyclic tests, wherein the response time and recovery time were determined to be 1.4 s and 1.7 s, respectively. Finally, the effects of temperature fluctuations and photobleaching on the sensor’s performance have been effectively corrected, enabling accurate oxygen concentration measurements in complex environments.

Nitroxides are stable organic free radicals with a wide range of applications. They have found applications in chemistry, biochemistry, biophysics, molecular biology, and biomedicine as EPR/NMR imaging techniques. As spin labels and probes, they are used in electron paramagnetic resonance (EPR) spectroscopy in the study of proteins, lipids, nucleic acids, and enzymes, as well as for measuring oxygen concentration in cells and cellular organelles, as well as tissues and intracellular pH. Their unique redox properties have allowed them to be used as exogenous antioxidants. In this review, we have discussed the chemical properties of nitroxides and their antioxidant properties. Furthermore, we have considered their use as radioprotectors and protective agents in ischemia/reperfusion in vivo and in vitro. We also presented other applications of nitroxides in protecting cells and tissues from oxidative stress and in protein studies and discussed their use in EPR/MRI.

Non-invasive and high sensitivity oxygen concentration measurement of penicillin vials in a short optical path by interference fringes suppression

During 2020-2021, the COVID-19 pandemic exposed significant vulnerabilities in hospital safety, with oxygen-related fires and explosions occurring at twice the usual rate. This highlighted insufficient preparedness for increased oxygen therapy demands and the associated risks of oxygen-enriched atmospheres. This study aimed to develop and test a smart monitoring system to detect increased oxygen concentrations in hospital environments, mitigating the risk of fires. Based on Internet of Things (IoT) technology, the system includes wireless sensors that measure oxygen levels at regular intervals and transmit the data to a database. Alerts are sent to hospital staff via short message service and e-mail when oxygen levels exceed predefined thresholds. The sensors were deployed in an intensive care unit and were validated through real-time measurements under hospital conditions. The system demonstrated high accuracy (±1%) in monitoring oxygen concentrations with low power consumption (345 µA for oxygen concentration measurements taken every minute). Notifications reliably informed staff of oxygen level thresholds, enabling timely interventions. The proposed IoT-based smart monitoring system is a cost-effective and efficient solution for improving safety in medical environments.

This review present two aspects regarding the oxygen regime in the development of the pre-implantation embryo: measurement of oxygen concentration in the genital tract (oviduct/uterus) of females of various mammalian species, taking into account the estrous cycle of the animal; development and optimization of the conditions for the development of the embryo in vitro, taking into account the concentration of oxygen in the culture medium. It has been shown that for the twelve mammalian species presented in the review, the value of oxygen concentration in the oviduct/uterus (regardless of the phase of the estrous cycle) is, as a rule, significantly lower than the oxygen concentration under normoxic conditions (~20% oxygen). The phenomenon of functioning under hypoxic conditions indicates the uniqueness of the pre-implantation mammalian embryo, given the evolutionary tendency of more highly organized life forms to life under normoxic conditions (~20% oxygen). The experimentally established fact of the development of an intact pre-implantation embryo under hypoxic conditions is consistent with the overwhelming majority of studies regarding the comparative analysis of the cultivation of pre-implantation embryos in vitro under various oxygen regimes.

A PtTFPP/PDMS composite modified by PFOCTS demonstrated superhydrophobic and oleophobic properties. It exhibited high oxygen sensitivity in a fuel-laden atmosphere.

A novel solid electrolyte sensor with considerably improved response times is presented. The new so-called eFIPEX [etched flux (Φ) probe experiment] is based on the FIPEX [flux (Φ) probe experiment] sensor applied for the measurement of molecular and atomic oxygen concentrations. A main application is the measurement of atmospheric atomic oxygen aboard sounding rockets up to altitudes of 250 km. eFIPEX employs a new manufacturing technique for its electrodes combining two manufacturing steps-the deposition of platinum films with a polyol process and electrochemical etching to carve out the electrode geometry. Selectivity toward atomic oxygen is achieved through gold plating. All work steps can be completed in ambient air. Electrodes with thicknesses of 200nm to 1.5μm are manufactured and characterized with optical and electron microscopy as well as with energy dispersive x-ray spectroscopy. It is shown that the significantly faster response times are related to pores in the platinum film reaching down to the substrate. The new eFIPEX were flown in comparison with conventional FIPEX sensors on the PMWE-2 sounding rocket flight showing significantly improved performance. Due to the easier fabrication and the superior transient behavior, this new sensor system will be preferentially used in future missions.

Fuel cell stacks are growing: both in numbers deployed in the field but also in terms of active electrode areas. The pursuit of higher-power applications and power densities means that cell active areas upwards of 400cm² are now commonplace. With larger electrodes comes an increased risk of non-uniform distributions of current density, temperature and reactant concentrations, which may lead in turn to locally-accelerated degradation and premature failure. Whilst detailed CFD/FEA modelling and simulation can help to refine designs, direct observations via in-situ and in-operando measurements are vital to verify model outputs and identify complex phenomena that models can fail to capture.Our group has developed three spatially-resolved diagnostic techniques along with instrumentation, measurement systems and software tools designed to make their application as straightforward as possible for the characterisation of large-format PEMFC MEAs.Spatially-resolved electrochemical impedance spectroscopy (SR-EIS) has been demonstrated using a commercially-available, segmented current sensor plate. A new software tool integrates a multiplexer for automated SR-EIS measurements, along with automatic equivalent circuit fitting and visualisation of spatially-resolved Ohmic, charge transfer and mass transport-related losses.A novel technique has been developed for the measurement of distributed electrochemical surface area (dECSA), allowing localised changes in ECSA resulting from non-uniform ageing to be determined for the first time.Finally, a chronoamperometric sensor array is demonstrated for the spatially-resolved measurement of in-plane oxygen concentration at the PEMFC cathode.In combination, these characterisation techniques offer a significant advance in PEMFC diagnostics, providing a deeper insight into non-uniform conditions and degradation in large-format PEMFCs.

Photodynamic therapy (PDT) relies on the interactions between light, photosensitizers, and tissue oxygen to produce cytotoxic reactive oxygen species (ROS), primarily singlet oxygen (1O2) through Type II photochemical reactions, along with superoxide anion radicals (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH) through Type I mechanisms. Accurate dosimetry, accounting for all three components, is crucial for predicting and optimizing PDT outcomes. Conventional dosimetry tracks only light fluence rate and photosensitizer concentration, neglecting the role of tissue oxygenation. Reactive oxygen species explicit dosimetry (ROSED) quantifies the reacted oxygen species concentration ([ROS]rx) by explicit measurements of light fluence (rate), photosensitizer concentration, and tissue oxygen concentration. Here we determine tissue oxygenation from non-invasive diffuse correlation spectroscopy (DCS) measurement of tumor blood flow using a conversion factor established preclinically. In this study, we have enrolled 24 pleural PDT patients into the study. Of these patients, we are able to obtain data on 20. Explicit dosimetry of light fluence, Photofrin concentration, and tissue oxygenation concentrations were integrated into the ROSED model to calculate [ROS]rx across multiple sites inside the pleural cavity and among different patients. Large inter- and intra-patient heterogeneities in [ROS]rx were observed, despite identical 60 J/cm2 light doses, with mean [ROS]rx,meas of 0.56 ± 0.26 mM for 13 patients with 21 sites, and [ROS]rx,calc1 of 0.48 ± 0.23 mM for 20 patients with 76 sites. This study presented the first comprehensive analysis of clinical ROSED in pleural mesothelioma patients, providing valuable data on future ROSED based pleural PDT that can potentially produce uniform ROS and thus improve the PDT efficacy for Photofrin-mediated pleural PDT.