Inherent Oxygen Research Articles

On Using the Volatile Mem-Capacitive Effect of TiO2 Resistive Random Access Memory to Mimic the Synaptic Forgetting Process

In this work, we report on mimicking the synaptic forgetting process using the volatile mem-capacitive effect of a resistive random access memory (RRAM). TiO2 dielectric, which is known to show volatile memory operations due to migration of inherent oxygen vacancies, was used to achieve the volatile mem-capacitive effect. By placing the volatile RRAM candidate along with SiO2 at the gate of a MOS capacitor, a volatile capacitance change resembling the forgetting nature of a human brain is demonstrated. Furthermore, the memory operation in the MOS capacitor does not require a current flow through the gate dielectric indicating the feasibility of obtaining low power memory operations. Thus, the mem-capacitive effect of volatile RRAM candidates can be attractive to the future neuromorphic systems for implementing the forgetting process of a human brain.

Comparing the structural development of sand and rock ilmenite during long-term exposure in a biomass fired 12 MWth CFB-boiler

Oxygen Carrier Aided Combustion (OCAC) is a novel combustion concept with the purpose to increase the overall efficiency in conventional circulating fluidized bed (CFB) boilers. By replacing the commonly used bed material with an oxygen carrier (OC), the conceptual idea is to utilize the fluid dynamics in a CFB and the inherent oxygen transport supported by the OC to increase the oxygen distribution within the furnace in time and space. The OCAC concept has been successfully validated and further reached long-term demonstration in full scale operation (75-MWth).This work presents a first evaluation of how ilmenite particles are affected in regard to mechanical resistance during long-term exposure to OCAC conditions in Chalmers 12-MWth CFB-boiler. A sand and a rock ilmenite are evaluated with regard to their mechanical stability. For evaluation, samples of the fresh materials and samples collected during operation in the Chalmers boiler are investigated. The study shows that the two materials differ in how the mechanical degradation occurs with exposure time. The sand ilmenite form cavities which are held together by an ash layer before they are shattered into numerous pieces, whereas the rock ilmenite develops distinct cracks that cause splitting of the particles.

Influence of inherent iron and oxygen concentrations on selenite sorption process using bentonite

The oxygen concentration and inherent Fe in bentonite have a significant influence on the Se(IV) sorption process. In this study, the sorption of selenite on natural bentonite was investigated using a batch experiment method, and the distribution coefficient ( K d) values were obtained in the pH range from 2.0 to 10.0 under oxic/anoxic conditions. The K d values always reached a maximum value at a pH of 4 under oxic conditions and at a pH of 8 under anoxic conditions; meanwhile, the K d value under anoxic conditions was larger than the value under oxic conditions, especially in regard to the maximum K d values. The oxygen conditions have a significant influence on the ratio of redox-sensitive Fe2+/Fe3+, which was closely related to the difference in the K d values under both oxic/anoxic conditions. Ferric selenite and green rust could be responsible for the maximum K d values under oxic/anoxic conditions. In the leaching experiments, we found that the Fe2+ in bentonite could replace Mg2+ and Al3+ in the octahedral sheet. Spectroscopy methods, such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) were used to characterize the surface properties of the samples after reaction. Overall, this study shows that the addition of Fe2+-containing materials into backfill/buffer materials under anoxic condition could enhance the sorption of 79Se(IV).

Microstructural Evolution during Pressureless Sintering of Blended Elemental Ti-Al-V-Fe Titanium Alloys from Fine Hydrogenated-Dehydrogenated Titanium Powder

A comprehensive study was conducted on microstructural evolution of sintered Ti-Al-V-Fe titanium alloys utilizing very fine hydrogenation-dehydrogenation (HDH) titanium powder with a median particle size of 8.84 μm. Both micropores (5–15 μm) and macropores (50–200 μm) were identified in sintered titanium alloys. Spherical micropores were observed in Ti-6Al-4V sintered with fine Ti at the lowest temperature of 1150 °C. The addition of iron can help reduce microporosity and improve microstructural and compositional homogenization. A theoretical calculation of evaporation based on the Miedema model and Langmuir equation indicates that the evaporation of aluminum could be responsible for the formation of the macropores. Although reasonable densification was achieved at low sintering temperatures (93–96% relative density) the samples had poor mechanical properties due mainly to the presence of the macroporosity and the high inherent oxygen content in the as-received fine powders.

Assessment of performance, combustion and emission characteristics of a direct injection diesel engine with solar driven Jatropha biomass pyrolysed oil

The paper is aimed to utilize pyrolysed oil (PO) as a fuel candidate in a direct injection diesel engine. Concentrated solar energy was used to produce pyrolysed oil from Jatropha biomass. The pyrolysed oil was upgraded and blended with diesel at 20%, 40%, and 60% shares (PODB20, PODB40, and PODB60). Experimental tests were conducted on a 3.7kW single cylinder compression ignition (CI) engine at different loads with base diesel and PO blended fuels. Experimental results showed the improvement in thermal efficiency of the engine with low percentage of PO shares (PODB20 and PODB40) as compared to base diesel however, it was decreased slightly with high percentage of PO share (PODB60). In-cylinder pressure was increased initially with addition of PO until 40% due to the dominant effect of inherent oxygen content, and then declined with further addition of PO due to the dominant effect of lower heating value and higher density of PO. Ignition delay and combustion duration were increased continually with increasing percentage of PO share. Unburnt hydrocarbons, carbon monoxide and smoke emissions initially decreased with lower PO shares (20% and 40%) due to high combustion temperature and later increased with higher PO share (60%), whereas oxides of nitrogen emission was followed the reverse trends. A clear insight obtained from the study is that blending of PO with diesel to a certain extent (until 40%) is beneficial in terms of higher thermal efficiency and lower emissions (all carbon based emissions) beyond which a slight penalty in the engine performance and emission characteristics was explored.

Controlled gas exchange in whole lung bioreactors.

In cellular, tissue-level or whole organ bioreactors, the level of dissolved oxygen is one of the most important factors requiring control. Hypoxic environments may lead to cellular apoptosis, while hyperoxic environments may lead to cellular damage or dedifferentiation, both resulting in loss of overall tissue function. This manuscript describes the creation, characterization and validation of a bioreactor system that can control oxygen delivery based on real-time metabolic demand of cultured whole lung tissue. A mathematical model describing and predicting gas exchange within the tunable bioreactor system is developed. In addition, the inherent gas exchange properties of the bioreactor and the inherent oxygen consumption rates of native rat lungs are determined, thereby providing a quantitative relationship between system parameters and levels of dissolved oxygen. Finally, the mathematical model is validated during whole lung culture under a range of system parameters. The system presented here provides a quantitative relationship between the concentration of dissolved oxygen, tissue oxygen consumption rates, and controllable system parameters that introduce gasses into the bioreactor. This relationship not only enables the maintenance of constant levels of dissolved oxygen throughout a culture period during which cells are replicating, but also provides noninvasive and real-time estimation of the metabolic and proliferative states of native or engineered lung tissue simply through dissolved oxygen measurements. Copyright © 2017 John Wiley & Sons, Ltd.

Enhanced magnetization and reduced leakage current by Zr substitution in multiferroic ScMnO3

Despite numerous attempts of electron doping in different manganites (RMnO3, R=rare earth), successful reports are scarce in the literature till date. In this paper, we have synthesized a series of phase-pure electron doped multiferroic compound Sc1−xZrxMnO3 (x=0, 0.05, 0.1, and 0.2) and evaluated the effect of doping on structural properties, oxidation states of cations, DC magnetization, heat capacity, resistivity, dielectric behaviour and ferroelectricity in the material. The presence of Zr4+ and mixed valence state of Mn comprising of Mn2+ and Mn3+ ions are confirmed using X-ray photoelectron spectroscopy. All these samples exhibit antiferromagnetic ordering; as Zr4+ content increases, antiferromagnetic ordering gradually diminishes while shifting to low temperatures. Additionally, ferromagnetic-like interaction develops in doped systems which gives rise to hysteresis in isothermal magnetization loops with greatly enhanced magnetization in comparison to pure antiferromagnetic nature of x=0 i.e. ScMnO3. Interestingly, even with zero magnetic moment of Sc3+, Schottky-like anomaly is observed at 5K in heat capacity data of samples with x=0.1 and 0.2, a result that we attribute to the highly resistive nature of doped samples. Moreover, while measuring ferroelectric hysteresis loops, we observe a significant reduction of leakage current in doped sample (x=0.2) compared to pure ScMnO3. Additionally, the compound x=0.2 shows improved dielectric and ferroelectric behaviour. It is proposed that doping of Zr4+ compensates for the cation deficiency and consequently eliminates the inherent oxygen vacancies by charge compensation.

Nanoencapsulation of Aloe vera in Synthetic and Naturally Occurring Polymers by Electrohydrodynamic Processing of Interest in Food Technology and Bioactive Packaging.

This work originally reports on the use of electrohydrodynamic processing (EHDP) to encapsulate Aloe vera (AV, Aloe barbadensis Miller) using both synthetic polymers, i.e., polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVOH), and naturally occurring polymers, i.e., barley starch (BS), whey protein concentrate (WPC), and maltodextrin. The AV leaf juice was used as the water-based solvent for EHDP, and the resultant biopolymer solution properties were evaluated to determine their effect on the process. Morphological analysis revealed that, at the optimal processing conditions, synthetic polymers mainly produced fiber-like structures, while naturally occurring polymers generated capsules. Average sizes ranged from 100 nm to above 3 μm. As a result of their different and optimal morphology and, hence, higher AV content, PVP, in the form of nanofibers, and WPC, of nanocapsules, were further selected to study the AV stability against ultraviolet (UV) light exposure. Fourier transform infrared (FTIR) spectroscopy confirmed the successful encapsulation of AV in the biopolymer matrices, presenting both encapsulants a high chemical interaction with the bioactive components. Ultraviolet-visible (UV-vis) spectroscopy showed that, while PVP nanofibers offered a poor effect on the AV degradation during UV light exposure (∼10% of stability after 5 h), WPC nanobeads delivered excellent protection (stability of >95% after 6 h). This was ascribed to positive interactions between WPC and the hydrophilic components of AV and the inherent UV-blocking and oxygen barrier properties provided by the protein. Therefore, electrospraying of food hydrocolloids interestingly appears as a novel potential nanotechnology tool toward the formulation of more stable functional foods and nutraceuticals.

Macroinvertebrate short-term responses to flow variation and oxygen depletion: A mesocosm approach

In Mediterranean rivers, water scarcity is a key stressor with direct and indirect effects on other stressors, such as water quality decline and inherent oxygen depletion associated with pollutants inputs. Yet, predicting the responses of macroinvertebrates to these stressors combination is quite challenging due to the reduced available information, especially if biotic and abiotic seasonal variations are taken under consideration. This study focused on the response of macroinvertebrates by drift to single and combined effects of water scarcity and dissolved oxygen (DO) depletion over two seasons (winter and spring). A factorial design of two flow velocity levels - regular and low (vL) - with three levels of oxygen depletion - normoxia, medium depletion (dM) and higher depletion (dH) - was carried out in a 5-artificial channels system, in short-term experiments. Results showed that both stressors individually and together had a significant effect on macroinvertebrate drift ratio for both seasons. Single stressor effects showed that macroinvertebrate drift decreased with flow velocity reduction and increased with DO depletion, in both winter and spring experiments. Despite single stressors opposing effects in drift ratio, combined stressors interaction (vL×dM and vL×dH) induced a positive synergistic drift effect for both seasons, but only in winter the drift ratio was different between the levels of DO depletion. Stressors interaction in winter seemed to intensify drift response when reached lower oxygen saturation. Also, drift patterns were different between seasons for all treatments, which may depend on individual's life stage and seasonal behaviour. Water scarcity seems to exacerbate the oxygen depletion conditions resulting into a greater drifting of invertebrates. The potential effects of oxygen depletion should be evaluated when addressing the impacts of water scarcity on river ecosystems, since flow reductions will likely contribute to a higher oxygen deficit, particularly in Mediterranean rivers.

Some factors influencing the fluidity of coal blends: Particle size, blend ratio and inherent oxygen species

The fluidity performance of blended coals prepared from caking coal and non- or slightly-caking coal of different particle sizes, and the evolution of gaseous oxygen containing compounds (CO, CO2 and H2O) during carbonization are examined using the Gieseler plastometer method, and a flow-type fixed-bed quartz made reactor, respectively. The heating rate and temperature are 3°C/min and 1000°C, respectively. The Gieseler fluidity decreases with increasing blend ratio of non- or slightly-caking coal to caking coal. In addition, the fluidity tends to decrease with the decreasing particle size of non- or slightly-caking coal in blended coals. The evolution of CO, CO2 and H2O during the carbonization of single coals begins at 200–400°C, and the main peak of the formation rate appears at 450–700°C. The amount of gaseous O-containing compounds evolved until 1000°C from the non- or slightly-caking coals is greater than that of evolved from the caking coal. Additionally, a negative correlation is observed between the amounts of CO, CO2, and H2O that evolve up to the initial softening temperature and the maximum fluidity value. The profiles of formation rates of the three gaseous O-containing compounds from the blended coal during carbonization are different with additive average based on the results of single coals. Furthermore, for the blended coal, the starting temperature H2O evolution measured shifts to higher temperature in comparison with that of calculated based on the results of single coals. Therefore, it is possible that the H2O produced from non- or slightly-caking coal in blended coal or that the H2O formation reactions in blended coal during carbonization affects the fluidity performance of the blended coal.

Impacts of thermal annealing temperature on memory properties of charge trapping memory with NiO nano-pillars

In this work, Au/SiO2/NiO/SiO2/Si structure charge trapping memory using NiO as the charge trapping layer was fabricated, and the impacts of the annealing temperature on the charge trapping memory performance were investigated in detail. The sample thermal annealed at 750°C indicated a large memory window of 2.07 V under a low sweeping voltage of ±5 V, which also has excellent charge retention properties with only small charge loss of ∼4.9% after more than 104 s retention. The high resolved transmission electron microscopy shows that the NiO films grew as nano-pillars structure. It is proposed that the excellent memory characteristics of the device are attributed to the inherent atomic defects and oxygen vacancies accumulated by the grain boundaries around NiO nano-pillars. Meanwhile the interface inter-diffusion formed by thermal annealing process is also an indispensable factor for the excellent memory characteristics of the device.

Endoscopic combustion characterization of Jatropha biodiesel in a compression ignition engine

Decline in global resources of petroleum based fuels such as diesel and gasoline have attracted attention of researchers towards alternative fuels which are capable of providing both, energy security and protection against environmental degradation due to emission of hazardous pollutants. As an oxygenated fuel, biodiesel has emerged as a potential alternative fuel, which can be used in diesel engines on large-scale to reduce CO, HC and PM emissions. In this experimental study, Jatropha curcas derived biodiesel (JB100) and its 20% (v/v) blend with mineral diesel (JB20) was tested in a production-grade single cylinder diesel engine for evaluating its combustion characteristics. Since soot and NOx emissions are major concerns in CI engine combustion, it is very important to investigate their in-situ spatial distribution, so that effective control measures can be devised. For this, endoscopic visualization technique was implemented on a modified prototype engine to evaluate the effect of biodiesel blending percentage and engine load on in-situ spatial distribution of in-cylinder soot and flame temperature distributions. Inherent oxygen content of biodiesel helped in achieving superior combustion; as a result, in-cylinder soot formation was lower than baseline mineral diesel. Spatial flame temperature distribution was also relatively lower in biodiesel. Endoscopic visualization technique was found to be effective in evaluating different combustion characteristics in a modified prototype engine.

Combustion performance and emission characteristics of a diesel engine under low-temperature combustion of pine oil–diesel blends

Pine oil is a biofuel derived from pine trees; its cetane number, kinematic viscosity, and boiling point are lower than those of diesel. Because of its inherent oxygen content, high calorific value, and good solubility, pine oil is considered as a potential alternative of diesel. In this work, we investigated the combustion and emission characteristics of pine oil–diesel blends in a high-speed four-cylinder turbocharged diesel engine under different loads and exhaust gas recirculation (EGR) rates. Four fuels, diesel blended with pine oil in proportions of 0%, 20%, 40%, and 50% (named as P0, P20, P40, and P50, respectively), were tested. The results show that when the load ranged from 40% to 100%, the equivalent brake specific fuel consumption (BSFC) of P50 was only 2.08–3.5% higher than that of P0, whereas that of P20 was <1% than pure diesel. The addition of pine oil to diesel decreased the soot emission, but NOx emission increased. For pine oil–diesel blends, with the increase in the EGR rate from 0 to 24.6%, the variations in the soot, CO, and THC emissions were not obvious, whereas the NOx emissions significantly decreased. Under the same EGR rate, with the increase in the proportion of pine oil, the NOx emissions increased; the effects of an increase in the EGR rate on the NOx emissions were higher than an increase in the pine oil fraction in the blend. When the EGR rate exceeded 24.6%, the soot, CO and, THC emissions sharply increased. However, it is possible to significantly reduce the soot emissions at a high EGR rate by increasing the blend proportion of pine oil.

Facile Preparation of Multifunctional WS2 /WOx Nanodots for Chelator-Free 89 Zr-Labeling and In Vivo PET Imaging.

While position emission tomography (PET) is an important molecular imaging technique for both preclinical research and clinical disease diagnosis/prognosis, chelator-free radiolabeling has emerged as a promising alternative approach to label biomolecules or nanoprobes in a facile way. Herein, starting from bottom-up synthesized WS2 nanoflakes, this study fabricates a unique type of WS2 /WOx nanodots, which can function as inherent hard oxygen donor for stable radiolabeling with Zirconium-89 isotope (89 Zr). Upon simply mixing, 89 Zr can be anchored on the surface of polyethylene glycol (PEG) modified WS2 /WOx (WS2 /WOx -PEG) nanodots via a chelator-free method with surprisingly high labeling yield and great stability. A higher degree of oxidation in the WS2 /WOx -PEG sample (WS2 /WOx (0.4)) produces more electron pairs, which would be beneficial for chelator-free labeling of 89 Zr with higher yields, suggesting the importance of surface chemistry and particle composition to the efficiency of chelator-free radiolabeling. Such 89 Zr-WS2 /WOx (0.4)-PEG nanodots are found to be an excellent PET contrast agent for in vivo imaging of tumors upon intravenous administration, or mapping of draining lymph nodes after local injection.

(Invited) Correlating Ion Transport with Structure in Interstitial Containing Oxides:Potential for New Electrolytes?

Development of oxide ion conducting devices such as sensors, fuel cells and permeation membranes, has traditionally relied on the optimisation of materials with lattice vacancies through substitution, increasing the vacancy content and consequently conductivity. Whilst the ionic conductivity is a key parameter it is also essential to understand the surface exchange kinetics, stability and compatibility with other functional components. For many of the perovskite and fluorite based ion conductors the process of increasing vacancy content through substitution induces chemical instabilities, including cation segregation, that leads to reactivity and ultimately degradation in lifetime. In an effort to address some of these issues and to extend the compositional space available to materials developers we have considered the use of materials with inherent oxygen interstitial content. A range of materials have been considered, mainly based on the scheelite framework, in which significant interstitial content can be accomodated. Two main series of oxide niobates are the subject of this study: CeNbO4+d and LaNbO4. In the first series of oxides the oxidation of the Ce3+ species on increasing temperature induces ordering and results in a fast ion transport pathway through these phases. Unusually these materials are also structurally modulated, and anisotropic in nature. The oxidation of the Ce species also induces electronic transport. Substitution of the Ce species with divalent cations did not significantly affect the ion transport. For the second series of oxides we have focused on hexavalent substitution of the Nb site to incorporate interstitials, modulate the structure and reduce the electronic transport. Here we will discuss the potential of these modulated scheelite oxides as ion conductors, demonstrate effective electrolyte performance and correlate the ion transport with the structure of the materials, using a suite of advanced characterisation techniques.

Influence of Inherent Oxygen Species on the Fluidity of Coal during Carbonization

The evolution of gaseous oxygen-containing species (CO, CO2, and H2O) during carbonization of 10 types of caking coals has been investigated mainly using a fixed-bed quartz reactor to reveal the influence of inherent oxygen species on the Gieseler fluidity of the coal particles. The heating rate and temperature were 3 °C/min and 1000 °C, respectively. CO evolution apparently started after 350 °C, and the rate profile for CO evolved showed the main or shoulder peak at about 650 °C in many cases. On the other hand, CO2 started to evolve at low temperatures of 200–250 °C for almost all of the coals, and the profile for the rate of CO2 evolution exhibited a main peak at 400–450 °C and a shoulder or small peak at about 600 °C in all cases. H2O formation occurred significantly between 400 and 800 °C, irrespective of coal type. The Gieseler fluidity analyses also revealed that the initial softening, maximum fluidity (MF), and resolidification temperatures of the 10 coals were in the ranges of 375–435, 435–480, a...

Application of waste cooking oil (WCO) biodiesel in a compression ignition engine

The comprehensive spray and combustion characteristics of waste cooking oil (WCO) biodiesel (B100) and conventional diesel fuels were investigated. The injection rate was measured by Bosch method and spray test was performed in a constant volume chamber under non-evaporating condition. The fuels were injected at injection pressures of 80 and 160MPa with injection durations of 625 and 410μs, respectively. From the injection rate experiment, the WCO biodiesel exhibited relatively longer injection delay than diesel due to higher viscosity. The WCO biodiesel also showed longer liquid tip penetration length and narrower spray angle regardless of fuel injection pressure. Nevertheless, the calculated equivalence ratio along the axial direction of spray proved that WCO biodiesel had lean fuel–air ratio compared to diesel due to inherent oxygen content in the fuel molecule.A series of engine experiments was performed to investigate the combustion and emission characteristics in an optically accessible compression ignition engine equipped with a common-rail system. The net indicated mean effective pressures (IMEPnet) of 0.16–0.93MPa were tested under an engine speed of 1400r/min. The fuel injection timing was modified from 60 to 0 crank angle degree (CAD) before top dead center (bTDC) by 5 CAD. The WCO biodiesel had a slightly lower peak of in-cylinder pressure and fuel efficiency than diesel due to lower heating value. In terms of emissions, the WCO biodiesel had benefits in reduction of carbon monoxide, unburned hydrocarbon and smoke emissions in conventional diesel operating condition. On the other hand, however, the emission characteristics were deteriorated as the injection timing was advanced and the engine load was increased. The combustion imaging showed that the WCO biodiesel had lower flame luminosity and shorter visible flame duration than diesel.

Influence of the hydrothermal dewatering on the combustion characteristics of Chinese low-rank coals

This study investigates the influence of hydrothermal dewatering performed at different temperatures on the combustion characteristics of Chinese low-rank coals with different coalification maturities. It was found that the upgrading process significantly decreased the inherent moisture and oxygen content, increased the calorific value and fixed carbon content, and promoted the damage of the hydrophilic oxygen functional groups. The results of oxygen/carbon atomic ratio indicated that the upgrading process converted the low-rank coals near to high-rank coals which can also be gained using the Fourier transform infrared spectroscopy. The thermogravimetric analysis showed that the combustion processes of upgraded coals were delayed toward the high temperature region, and the upgraded coals had higher ignition and burnout temperature. On the other hand, based on the higher average combustion rate and comprehensive combustion parameter, the upgraded coals performed better compared with raw brown coals and the Da Tong bituminous coal. In ignition segment, the activation energy increased after treatment but decreased in the combustion stage. The changes in coal compositions, microstructure, rank, and combustion characteristics were more notable as the temperature in hydrothermal dewatering increased from 250 to 300 °C or coals of lower ranks were used.

(Invited) Enhanced Steam Electrolysis at Exsolution Titanates

B-site doped, A-site deficient perovskite titanate oxides with formula (M = Ni2+ or Fe3+; x = 0.06; g = (4-n)x/2) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis (HTSE) at 900 °C. A proportion of B-site dopants were exsolved at the surface in the form of metallic nanoparticles under SOEC operating (reducing) conditions, due in part to the inability of the host lattice to accommodate vacancies (introduced (d) oxygen vacancies () and fixed A-site () and inherent (g) oxygen vacancies) beyond a certain limit. The presence of electrocatalytically active Ni0 or Fe0 nanoparticles and higher concentrations dramatically lowered the activation barrier to steam electrolysis and led to sharp rises in oxide ion mobility compared to the parent material (x = 0). La0.4Sr0.4Ni0.06Ti0.94O2.94 demonstrated discontinuous temperature dependence possibly due to oxygen vacancy trapping at lower temperatures.

(Keynote) Oxygen Sensing Microfluidic Structures for Biomedical and Environmental Science Research

Planar optode films consisting of a fluorescent dye in a polymer film can be incorporated into microfluidic structures to map out oxygen concentrations while microfluidic devices set up gradients and environmental conditions that are relevant to biomedical or natural biogeochemical systems. Gradients of molecular oxygen are of particular interest due to the fact that many important biological processes either occur at interfaces or are regulated by the flux of oxygen and other resources. Hence, oxygen sensing microfluidic devices can be used to investigate microbial behavior related to carbon cycling, or microbial communities in the gut where the interface with the host tissue is microoxic. In addition, oxygen sensing microfluidic devices may be useful in mammalian cell or tissue culture where favorable conditions must be maintained. Practical issues in developing and fabricating microfluidic structures with inherent oxygen sensing capability include multiple parameters, including incorporation of sensing elements in microfluidics, imaging oxygen concentrations by fluorescence, and relating oxygen imaging data to spatial structure of the microfluidic channels, all in useful structures that create biologically relevant microenvironments. We will describe multiple approaches to meeting these challenges, including gas impermeable silicon-on-glass structures where the fluorescent signals are only observed where microfluidic channels occur, and solvent imprinting lithography where sensing dyes can be incorporated in thermoplastics in a single process that enables sensor dye impregnation, channel imprinting, and cover plate bonding. These methods are discussed with regard to structures including pore network and gradient generation microfluidic structures.