Measurement Of Oxygen Concentration Research Articles

Noninvasive Absolute Electron Paramagnetic Resonance Oxygen Imaging for the Assessment of Tissue Graft Oxygenation

Oxygen is the single most important molecule for sustaining life and, therefore, an important variable in tissue engineering and regenerative medicine. It has been shown that the change in oxygen concentration in an artificial or tissue-engineered graft affects cell survival, differentiation, and tissue growth in profound ways. However, at present, there are no reliable methods to map partial oxygen pressure (pO2) in growing artificial tissues. Here, we adapt and test the suitability of electron paramagnetic resonance oxygen imaging (EPROI) in assessing tissue graft oxygenation in vitro. EPROI is an established method to assess absolute pO2 and has been widely applied to study tumor hypoxia in small animals. In this study, we demonstrate the feasibility of EPROI in evaluating oxygen dynamics in tissue grafts. We measured oxygen concentration in mesenchymal stem cell (MSC)-seeded polylactic-co-glycolic acid (PLGA) scaffolds with variable porosity. The pO2 maps of these scaffolds showed that the mean pO2 inside the scaffolds was smaller than the ambient air pO2 (21% oxygen, 160 torr) and was gradually increased with increasing pore size. We assessed the local oxygen dynamics of the MSC-seeded osteogenic scaffold made from collagen-chitosan hydrogels in a partially sealed Eppendorf tube. The change in pO2 values as a function of time inside the graft showed that the cells had used available oxygen within first 2 h of the experiment and then went to a dormant low oxygen consumption state until the oxygen supply was reestablished. Collectively, these data suggest that EPROI could be successfully used for mapping pO2 in tissue-engineered grafts. The knowledge of tissue graft oxygenation may be used to improve scaffold design and to assess the tissue viability and growth.

A MEMS approach to determine the biochemical oxygen demand (BOD) of wastewaters

A MEMS approach to obtain an efficient tool for the evaluation of the biochemical oxygen demand (BOD) of wastewaters is introduced. Its operating principle is based on the measurement of oxygen concentration in water samples containing organic pollutants and specific bacteria. The microsystem has been designed to perform multiple and parallel measurements in a poly-wells microfluidic device. The monitoring of the bacterial activity is ensured by optical sensors incorporated in each well of the fluidic network. By using an optode sensor, it is hereby demonstrated that this approach is efficient to measure organic pollutants by testing different Luria Bertani buffer dilutions. These results also show that it is possible to reduce the duration of measurements from 5 d (BOD5) of the standard approach to few hours, typically 3 h–5 h.

Measurement of oxygen concentrations in bacterial biofilms using transient state monitoring by single plane illumination microscopy

Oxygen is required for respiration in aerobic bacteria and hence plays an essential role in the generation of energy necessary for cell maintenance and growth. The distribution of oxygen within a biofilm can be heterogeneous and may result in bacterial cells exhibiting distinct physiological states depending on their local oxygen availability. Here, we have employed transient state (TRAST) monitoring, a non-invasive method that can measure the relative populations of triplet states by time-modulated illumination, to determine the distribution of oxygen concentrations in biofilm colonies. The method was implemented on a single plane illumination microscope that can perform optical slicing, making it a suitable approach for imaging thick samples. We present a map of triplet relaxation times measured inside a Pseudomonas aeruginosa biofilm at micrometre resolution. We also provide a calibration method that can evaluate oxygen concentration based on TRAST contrast. Our results indicate that anoxic zones exist within the colonies, and oxygen consumption extends outside the areas of high cell densities, establishing a gradient until levels return to air saturation.

Fluorescence measurement of atomic oxygen concentration in a dielectric barrier discharge

Concentration of atomic oxygen was measured in a volume dielectric barrier discharge (DBD) ignited in mixtures of Ar + O2(+ H2) at atmospheric pressure. Two-photon absorption laser induced fluorescence (TALIF) of atomic oxygen was used and this method was calibrated by TALIF of Xe in a mixture of argon and a trace of xenon. The calibration was performed at atmospheric pressure and it was shown that quenching by three-body collisions has negligible effect on the life time of excited Xe atoms. The concentration of atomic oxygen in the DBD was around 1021 m−3 and it was stable during the whole discharge period. The concentration did not depend much on the electric power delivered to the discharge provided that the power was sufficiently high so that the visible discharge filled the whole reactor volume. Both the addition of hydrogen or replacing of argon by helium led to a significant decrease of atomic oxygen concentration. The TALIF measurements of O concentration levels in the DBD plasma performed in this work are made use of e.g. in the field analytical chemistry. The results contribute to understanding the processes of analyte hydride preconcentration and subsequent atomization in the field of trace element analysis where DBD plasma atomizers are employed.

High Resolution Measurements of Nitrous Oxide (N2O) in the Elbe Estuary

Nitrous oxide (N2O) is one of the most important greenhouse gases and a major sink for stratospheric ozone. Estuaries are sites of intense biological production and N2O emissions. We aimed to identify hot-spots of N2O production and potential pathways contributing to N2O concentrations in the surface water of the tidal Elbe estuary. During two research cruises in April and June 2015, surface water N2O concentrations were measured along the salinity gradient of the Elbe estuary by using a laser-based on-line analyzer coupled to an equilibrator. Based on these high-resolution N2O profiles, N2O saturations and fluxes across surface water/atmosphere interface were calculated. Additional measurements of DIN concentrations, oxygen concentration, and salinity were performed. Highest N2O concentrations were determined in the Hamburg port region reaching maximum values of 32.3 nM in April 2015 and 52.2 nM in June 2015. These results identify the Hamburg port region as a significant hot spot of N2O production, where linear correlations of AOU-N2Oxs indicate nitrification as an important contributor to N2O production in the freshwater part. However, in the region with lowest oxygen saturation, sediment denitrification obviously affected water column N2O saturation. The average N2O saturation over the entire estuary was 201% (SD: ± 94%), with an average estuarine N2O flux density of 48 µmol m-2 d-1 and an overall emission of 0.18 Gg N2O y-1. In comparison to previous studies, our data indicate that N2O production pathways over the whole estuary freshwater part have changed from predominant denitrification in the 1980s towards significant production from nitrification in the present estuary. Despite a significant reduction in N2O saturation compared to the 1980s, N2O concentrations nowadays remain on a high level, comparable to the mid 90s, although a steady decrease of DIN inputs occurred over the last decades. Hence, the Elbe estuary still remains an important source of N2O to the atmosphere.

Industrial-scale investigations of anthracite combustion characteristics and NOx emissions in a retrofitted 300 MWe down-fired utility boiler with swirl burners

To burn anthracite and reduce NOx emissions, a new combustion system was applied to a 300 MWe Babcock & Wilcox (B&W) down-fired boiler that included overfire air (OFA) and a decreased flow area of the inner and outer secondary air ducts of the installed swirl burners. Industrial-scale measurements (adjusting OFA ratios from 15.4% to 22.6%) were conducted to evaluate the overall performance of the retrofitted boiler. The experimental results demonstrated that the new combustion system promoted coal/air flow ignition and combustion stability. When the OFA ratio was less than 19.7%, the influence of the burner secondary air ratio on coal/air flow ignition was greater than that of the recirculation region below the arches. The overall combustion level in the primary combustion zone depended on the oxygen content and the recirculation region in the lower furnace instead of the early or late ignition of the coal/air flow. Oxygen and carbon monoxide concentration measurements in the near-sidewall region revealed that the fullness degree of the coal flame varied under different OFA ratios. Considering both environmental and economic effects, 19.7% was chosen as the optimal OFA ratio, thereby achieving a significant NOx reduction of 47% without increasing carbon content in the fly ash.

Regulation of benthic oxygen fluxes in permeable sediments of the coastal ocean

AbstractLarge areas of the oceanic shelf are composed of sandy sediments through which reactive solutes are transported via porewater advection fueling active microbial communities. The advective oxygen transport in permeable sands of the North Sea was investigated under in situ conditions using a new benthic observatory to assess the dynamic interaction of hydrodynamics, sediment morphodynamics, and oxygen penetration depth. During 16 deployments, concurrent measurement of current velocity, sediment topography, and porewater oxygen concentration were carried out. In all cases the oxyclines were found at depths of 1–6 cm, correlating with the topography of stationary and migrating bedforms (ripples). Different conditions in terms of bottom water currents and bedform migration led to fluctuating oxygen penetration depths and, hence, highly variable redox conditions in up to 2.5 cm thick layers beneath the surface. Volumetric oxygen consumption rates of surface sediments were measured on board in flow‐through reactors. Bedform migration was found to reduce consumption rates by up to , presumably caused by the washout of organic carbon that is otherwise trapped in the pore space of the sediment. Based on the observations we found oxygen penetration depths to be largely controlled by oxygen consumption rates, grain size, and current velocity. These controlling variables are summarized by an adapted Damköhler number which allows for prediction of oxygen penetretion depths based on a simple scaling law. By integrating the oxygen consumption rates over the oxygen penetration depth, oxygen fluxes of 8–34 mmol m−2 d−1 were estimated.

Characterization of strongly scattering nanoporous materials as miniaturized multipass cell for tunable diode laser absorption spectroscopy

Through the confinement of gas in nanoporous materials, it is possible to significantly increase the path length for light–gas interaction. This enables the observation of much stronger absorption features for the confined gas molecules. In this work, we systematically characterized a variety of disordered strongly scattering ZrO $$_2$$ and Al $$_2$$ O $$_3$$ nanoporous ceramic materials to exploit the potential of gas in scattering media absorption spectroscopy. As a result, we identified a material with an unprecedented performance in terms of optical path length enhancement. In ZrO $$_2$$ with thicknesses above 6 mm, the path enhancement exceeds 1000. The results obtained with near-infrared absorption spectroscopy on oxygen were validated by time-of-flight measurements at 700 nm, thus demonstrating their robustness. Finally, we report quantitative oxygen concentration measurement using nanoporous materials as miniaturized random-scattering multipass cell with an extremely simple and low-cost setup.

Advances in Hypoxia-Mediated Mechanisms in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the fifth most common and the third most deadly malignant tumor worldwide. Hypoxia and related oxidative stress are heavily involved in the process of HCC development and its therapies. However, direct and accurate measurement of oxygen concentration and evaluation of hypoxic effects in HCC prove difficult. Moreover, the hypoxia-mediated mechanisms in HCC remain elusive. Here, we summarize recent major evidence of hypoxia in HCC lesions shown by measuring partial pressure of oxygen (pO2), the clinical importance of hypoxic markers in HCC, and recent advances in hypoxia-related mechanisms and therapies in HCC. For the mechanisms, we focus mainly on the roles of oxygen-sensing proteins (i.e., hypoxia-inducible factor and neuroglobin) and hypoxia-induced signaling proteins (e.g., matrix metalloproteinases, high mobility group box 1, Beclin 1, glucose metabolism enzymes, and vascular endothelial growth factor). With respect to therapies, we discuss mainly YQ23, sorafenib, 2-methoxyestradiol, and celastrol. This review focuses primarily on the results of clinical and animal studies.

High-resolution Respirometry to Assess Mitochondrial Function in Permeabilized and Intact Cells.

A high-resolution oxygraph is a device for measuring cellular oxygen consumption in a closed-chamber system with very high resolution and sensitivity in biological samples (intact and permeabilized cells, tissues or isolated mitochondria). The high-resolution oxygraph device is equipped with two chambers and uses polarographic oxygen sensors to measure oxygen concentration and calculate oxygen consumption within each chamber. Oxygen consumption rates are calculated using software and expressed as picomoles per second per number of cells. Each high-resolution oxygraph chamber contains a stopper with injection ports, which makes it ideal for substrate-uncoupler-inhibitor titrations or detergent titration protocols for determining effective and optimum concentrations for plasma membrane permeabilization. The technique can be applied to measure respiration in a wide range of cell types and also provides information on mitochondrial quality and integrity, and maximal mitochondrial respiratory electron transport system capacity.

Effect of polymer matrix on the photophysical behaviors of pressure sensitive films

Based on the oxygen quenching of the luminescent intensity of the excited chromophoric probes in polymer matrix, pressure sensitivity paint film was particularly of interest to oxygen concentration or partial pressure measurement. The photophysical behaviors, especially the oxygen pressure sensitivity of pressure sensitive film are not only affected by the luminescence probes, but also by the polymer matrix.The photophysical behaviors of the pressure sensitive films composed of platinum tetra(pentafluorophyenyl)porphine (PtTFPP) in the polymer matrix of polymethylmethacrylate (PMMA), polybutylmethacrylate (PBMA), ethyl cellulose (EC) or ethylene-vinyl acetate copolymer (EVA) were investigated in this article. The results confirmed that all of the oxygen permeability of the polymer matrix, the molecular interaction between the probes and polymer and the depth distribution of the probes in the polymer matrix showed significant influence on the photophysical properties, oxygen quenching and pressure sensitivity of the pressure sensitive films.

Oxygen Concentration Measurement in the Porous Cathode of Lithium-air Battery by Fine Optical Fiber Sensor

Oxygen Concentration Measurement in the Porous Cathode of Lithium-air Battery by Fine Optical Fiber Sensor

Automated Calibration of Electrochemical Oxygen Sensors for Use in Compost Bedded Pack Barns

Abstract. The objective of this study was to develop an automated calibration process for a galvanic cell type oxygen sensor. The manufacturer recommended a two-point calibration at room temperature; however, testing revealed that the response was not linear when both the temperature and oxygen concentrations varied. Thus, additional points were needed to generate a representative calibration equation and to reduce the sensor prediction interval. The calibration process needed to be capable of automatically recording sensor response (voltage) at an array of temperatures and oxygen concentrations. Calibration gases were used to precisely control the oxygen concentration inside a small manifold, and an electronically controlled water bath was used to regulate the sensor and gas temperature. A custom computer program controlled the sampling order and the data collection process. The responses for three sensors were recorded at six temperature (10°C, 20°C, 30°C, 40°C, 50°C, and 60°C) and five oxygen concentration (0%, 5%, 10%, 15%, and 20% O2 absolute) combinations, for a total of 30 measurements per calibration. Calibration data were used to create a second-degree polynomial model with oxygen sensor voltage and temperature as input parameters, which reduced the prediction interval by over 1% O2 for each of the three sensors tested. The resulting prediction intervals ranged between 0.75% and 0.95% O2. Three sensors were mounted in a prototype oxygen probe and tested under controlled conditions to demonstrate the ability to measure oxygen concentration versus depth in a composting environment. Keywords: Aeration, Calibration, Compost, Dairy, Housing, Oxygen.

Is oxygen reduction a viable antioxidant strategy for oil‐in‐water emulsions?

The impact of 0, 40, 58, 79, 93, and 98% total oxygen reduction on lipid oxidation kinetics in a 1.0% fish oil‐in‐water emulsion (pH 3.0; 32°C) was determined. Atmospheres were modified using nitrogen/oxygen gas blends or high purity nitrogen. Headspace and dissolved oxygen were monitored throughout the study using a non‐destructive technique in which fluorescent sensors were fixed in sealed vials. Lipid oxidation, as measured by lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS), was inhibited at oxygen reductions ≥58%. However, meaningful protection against lipid oxidation was only achieved at oxygen reductions ≥93%. Potential commercial strategies, nitrogen flushing/sparging, and ascorbic acid, were inefficient at reducing oxygen to levels that could significantly inhibit lipid oxidation. Results suggest that near complete oxygen removal is necessary to protect oxygen‐sensitive ingredients, but a need still exists to identify new strategies that sufficiently reduce the oxygen content of emulsions.Practical applications: The practical application of this work is that there is a global demand to remove synthetic additives from food and beverage formulations, and as described in this work, defining the level oxygen reduction that provides meaningful increases in oxidative stability is necessary. Results suggest that the oxidative stability of 1% fish oil‐in‐water emulsions can be extended by reducing system oxygen by ∼58%, but to have a meaningful antioxidant impact greater than ∼93% oxygen removal is required. Further investigation into simulated commercial oxygen removal strategies (e.g., nitrogen displacement of oxygen and ascorbic acid) demonstrated that current industrial strategies are lacking and need to be optimized in order to enhance stability against lipid oxidation.In this work, we design and modify a fish oil‐in‐water emulsion system to have different oxygen concentrations that range from almost complete oxygen removal to atmospheric conditions. The resulting emulsions are characterized over time by non‐destructively measuring oxygen concentrations, both in the headspace and dissolved phase, as shown in the figure of two sensor patches inside a sealed glass vial. The impact of oxygen concentrations on lipid oxidation kinetics is measured and represented in the graphed data. Results suggest that near complete oxygen removal is necessary to provide meaningful protection against lipid oxidation in emulsified systems.

Improving the efficiency of fuel combustion with regard to the uncertainty of measuring oxygen concentration

This paper presents a new approach to control and mange the process of fuel combustion in the boiler units. Ways to increase the efficiency of combustion of fuel materials are examined. We proposed a method for indirect measurement of the current concentration of oxygen in the air whose magnitude quantity depends on meteorological environmental parameters: temperature, absolute pressure and relative humidity. Experimental research was conducted to compare direct and indirect methods of measuring the volumetric concentration of oxygen in the air. We calculated the uncertainties of measurement of the volumetric concentration of oxygen in the air for the direct and indirect methods. An estimation of the extended expanded uncertainty of the indirect method of measurement was carried out by the imitation simulation using the Monte-Carlo method. It is demonstrated that relative air humidity exerts the largest influence on the extended expanded uncertainty of measuring the volumetric concentration of oxygen. A comparison of the methods of measuring the volumetric concentration of oxygen revealed that the extended expanded uncertainty of the indirect method is less than that of the direct method. We proposed functional dependence of an increase in accuracy of the measurement of excess air coefficient that is based on the calculation of the current concentration of oxygen in the air, which will make it possible to ensure highly effective fuel combustion in the boiler units at any regimes of its functioning.

Development of an Electrochemical Oxygen Sensor for Liquid Sodium Using a Yttria Stabilized Zirconia Electrolyte

An accurate means of measuring oxygen concentration in sodium is crucial to characterizing the corrosion of sodium-cooled fast reactor (SFR) materials. Significant improvements with regards to lifetime/sensitivity/temperature threshold/etc. can be made to current Galvanic-cell oxygen sensing technology, so extensive research has been conducted at the University of Wisconsin-Madison to address these issues. Electrochemical oxygen sensors using yttria-stabilized zirconia (YSZ) electrolytes were designed and tested in liquid sodium up to 400[°C]. These sensors produced an oxygen-dependent signal, and this signal followed the expected functional form, but the lifetime and reproducibility of the sensors were inadequate for commercial use. Sensor performance was analyzed and temperature effects on ionic conductivity, non-bulk thermodynamics, and YSZ-based issues were quantified to study deviations from theory in both slope and signal offset.

Reticulated porous ceria undergoing thermochemical reduction with high-flux irradiation

A numerical and experimental analysis is performed on the solar-driven thermochemical reduction of ceria as part of a H2O/CO2-splitting redox cycle. A transient heat and mass transfer model is developed to simulate reticulated porous ceramic (RPC) foam-type structures, made of ceria, exposed to concentrated solar radiation. The RPC features dual-scale porosity in the mm-range and μm-range within its struts for enhanced transport. The numerical model solves the volume-averaged conservation equations for the porous fluid and solid domains using the effective transport properties for conductive, convective and radiative heat transfer. These in turn are determined by direct pore-level simulations and Monte-Carlo ray tracing on the exact 3D digital geometry of the RPC obtained from tomography scans. Experimental validation is accomplished in terms of temporal temperature and oxygen concentration measurements for RPC samples directly irradiated in a high-flux solar simulator with a peak flux of 1200 suns and heated to up to 1940K. Effective volumetric absorption of solar radiation was obtained for moderate optically thick structures, leading to a more uniform temperature distribution and a higher specific oxygen yield. The effect of changing structural parameters such as mean pore diameter and porosity is investigated.

Oxygen concentration and mobility in conserved archaeological wood

Probes for measuring oxygen concentration were installed inside large samples of conserved wood from archaeological shipwrecks to record oxygen profiles as a function of depth under the wood surface. The concentration of oxygen was lower inside the wood than outside indicating that the supply of oxygen is limited and that oxygen is consumed within the material. This was confirmed by oxygen consumption rates averaging 1.3 ± 0.42 µg O2/g wood/day. The diffusion properties were estimated by placing the wood samples in a nitrogen atmosphere and measuring nitrogen breakthrough time to the oxygen probes at different depths. A high level of variation was observed between the breakthrough times measured at different depths of the samples. This indicated that the access of oxygen is irregular, possibly due to wood heterogeneity and uneven distribution of conservation agent. By recording oxygen concentrations inside archaeological wood under stable environmental conditions, it was shown that oxygen concentration profiles are almost constant over a time span of seven years. This indicates that oxygen consumption, and thus oxidative degradation, is constant for an extended period of time. It also shows that the oxygen concentration inside conserved archaeological wood is a steady state value controlled by the local balance between oxygen supply and oxygen consumption.

Evaluation of the 2-(1-Hexyloxyethyl)-2-devinyl pyropheophorbide (HPPH) mediated photodynamic therapy by macroscopic singlet oxygen modeling.

Photodynamic therapy (PDT) is known as a non-invasive treatment modality that is based on photochemical reactions betweenoxygen, photosensitizer, and a special wavelength of light. However, a dosimetric predictorfor PDT outcome is still elusive because current dosimetric quantities do not account for the differences in the PDT oxygen consumption rate for different fluence rates. In this study, we evaluate several dose metrics, total fluence, photobleaching ratio, PDT dose, and mean reacted singlet oxygen (mean [1 O2 ]rx ) for predicting the PDT outcome and a clinically relevant tumor re-growth endpoint. For this reason, radiation-induced fibrosarcoma (RIF) mice tumors are treatedwith 2-(1-Hexyloxyethyl)-2-devinyl pyropheophorbide (HPPH) and different in-air fluences (30J/cm2 , 50J/cm2 , 135J/cm2 , 250J/cm2 , and 350J/cm2 ) and in-air fluence rates (20, 50, 75, 150mW/cm2 ). Explicit measurements of HPPH and oxygen concentration as well as tissue optical properties are performed pre- and post-treatment. Then, this information is incorporated into a macroscopic model to calculate the photobleaching, PDT dose, and mean [1 O2 ]rx . Changes in tumor volume are tracked following the treatment and compared with the dose metrics. The correlation demonstrates that mean [1 O2 ]rx serves as a better dosimetric quantity for predicting treatment outcome and a clinically relevant tumor re-growth endpoint.

Non-Destructive Optical Measurement of Oxygen Concentration on PEFC Catalyst Layer

Tiny optical fiber sensor was applied to realize non-destructive measurement of oxygen concentration on PEFC catalyst layer.Insufficient supply of oxygen to the cathode catalyst layer caused by transport resistance is critical issue. Fundamental study in order to achieve efficient oxygen transport is required, however; non-destructive and in-situ measurement of oxygen concentration on the catalyst layer was not achieved. In this study, oxygen concentration on the catalyst layer under operating condition was measured by using a tiny optical fiber and oxygen indicator.Figure 1 shows experimental setup. Platinum tetrakis pentrafluoropheny porphine (PtTFPP) was employed as oxygen indicator[1]. When the PtTFPP is exposed to excitation light (l = 405 nm), phosphorescence emission (l = 650 nm) is produced. Phosphorescence intensity is determined by oxygen partial pressure. Thus, quantitative oxygen concentration can be obtained by measuring phosphorescence intensity and using calibration data. In this study, PtTFPP was painted at the edge of fused silica optical fiber of which diameter was 110 mm. In order to measure the phosphorescence intensity, bifurcated optical fibers were connected to excitation light source and spectrometer, respectively.The cell has an active area of 4 cm2 (2 × 2 cm) with straight channels. The channel width and depth were 1.0 and 1.0 mm, respectively, and the rib-to-channel ratio was 1. The carbon paper GDL without MPL (SIGRACET®24BA, SGL Group, USA) was used for both the anode and the cathode side. In order to measure the oxygen concentration on the catalyst layer with reducing insertion effect, optical fiber was inserted from the intrinsic large pore of GDL without boring a hole, and the edge of the fiber was touched on the catalyst layer surface. Flow rates of hydrogen and air were 50NmL/min and 125 NmL/min, respectively. Cell was operated under 33 °C because phosphorescence intensity becomes low under high temperature. Bubbler temperature was 22 °C (relative humidity was 50%)In the experiment, cell voltage was varied from 0.9 V to 0.2 V, and change of current density and oxygen concentration were measured. Figure 2 shows current-voltage (IV) characteristics. In the higher current density condition, variation of plots suggests emergence of flooding in the cathode. Since the flooding decreased gas diffusivity in the cathode catalyst layer, IV characteristics fluctuate at high current density and low cell voltage condition. As shown in Figure 3, change of oxygen concentration on the catalyst layer was measured successfully. Oxygen concentration decreases monotonically with decreasing cell voltage. Minimum value of the concentration was below 2 % at 0.2 V cell voltage. Figure 2 indicated that total cell performance was declined by flooding. On the other hand, local oxygen concentration of the catalyst layer was able to be measured by using a tiny optical fiber. Figure 3 shows large amount of oxygen was still consumed under high current density and it means that power generation concentrated on local surface of the catalyst layer where surface not covered with the liquid water.As discussed above, oxygen concentration on cathode catalyst layer was measured non-destructively. This technique holds further potential to measure oxygen transport phenomena on the catalyst layer under 60-80 °C cell operation by improving optical oxygen sensor sensitivity. AcknowledgementThis study is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Experimental setup in present study was assisted by Yoshihiko Aoki (Tokyo Institute of Technology). Reference[1] CS Chu., CA Lin, Sensors and Actuators B: Chemica, 2014, 195, 259-265. Figure 1