Monitoring Of Oxygen Levels Research Articles

Increasing the Oxygen Consumption in Hermetic Grain Storage Using Grain Weevils (Sitophilus granarius)

Loss of stored plant products due to insect infestation is a problem that is likely to increase with global warming. Improved storage under hermetic conditions in oxygen deficiency can prevent or control infestation and preserve product quality. Oxygen levels in hermetic storage decrease due to different factors, one of which is the oxygen consumption of the insects present. Experiments were carried out using varying numbers (25, 50, or 200) of all developmental stages of the grain weevil Sitophilus granarius L. (eggs, larvae, pupae, and adult beetles) caged and placed in sealed 30-L containers containing 22 kg of wheat for at least 21 weeks. Oxygen levels were measured at regular intervals. The oxygen consumption depended on the number of insects and went below the critical threshold of 3% for S. granarius survival in most of the trials. Some surviving beetles were observed at the end of the hermetic experiments and 12 weeks afterwards during control for progeny, when oxygen levels did not fall below the critical threshold or the low level could not be maintained for a sufficient time. Monitoring oxygen levels in hermetic storage is therefore essential to ensure safe storage over long periods.

Hypoxia Primes Human ISCs for Interleukin-Dependent Rescue of Stem Cell Activity

Hypoxia in the intestinal epithelium can be caused by acute ischemic events or chronic inflammation in which immune cell infiltration produces inflammatory hypoxia starving the mucosa of oxygen. The epithelium has the capacity to regenerate after some ischemic and inflammatory conditions suggesting that intestinal stem cells (ISCs) are highly tolerant to acute and chronic hypoxia; however, the impact of hypoxia on human ISC (hISC) function has not been reported. Here we present a new microphysiological system (MPS) to investigate how hypoxia affects hISCs from healthy donors and test the hypothesis that prolonged hypoxia modulates how hISCs respond to inflammation-associated interleukins (ILs). hISCs were exposed to <1.0% oxygen in the MPS for 6, 24, 48, and 72 hours. Viability, hypoxia-inducible factor 1a (HIF1a) response, transcriptomics, cell cycle dynamics, and response to cytokines were evaluated in hISCs under hypoxia. HIF stabilizers and inhibitors were screened to evaluate HIF-dependent responses. The MPS enables precise, real-time control and monitoring of oxygen levels at the cell surface. Under hypoxia, hISCs maintain viability until 72 hours and exhibit peak HIF1a at 24 hours. hISC activity was reduced at 24 hours but recovered at 48 hours. Hypoxia induced increases in the proportion of hISCs in G1 and expression changes in 16 IL receptors. Prolyl hydroxylase inhibition failed to reproduce hypoxia-dependent IL-receptor expression patterns. hISC activity increased when treated IL1β, IL2, IL4, IL6, IL10, IL13, and IL25 and rescued hISC activity caused by 24 hours of hypoxia. Hypoxia pushes hISCs into a dormant but reversible proliferative state and primes hISCs to respond to a subset of ILs that preserves hISC activity. These findings have important implications for understanding intestinal epithelial regeneration mechanisms caused by inflammatory hypoxia.

DESIGN &amp; CONSTRUCTION OF OXYGEN SATURATION MEASURING EQUIPMENT THROUGH THE THINGSPEAK SERVER WITH MAX 30100 SENSOR

The human body requires sufficient oxygen levels for daily life, so it is important for humans to maintain oxygen levels in their bodies. Good oxygen saturation will facilitate the distribution of substances in the body, red blood cells carry oxygen from the lungs and are distributed throughout the body. It is very important for humans to keep oxygen within normal limits. Excess oxygen in the blood or hyperoxaemia: above 120 mmHg. The normal limits for oxygen levels in human blood are between: 75-100 mmHg. Lack of oxygen or hypoxaemia is less than 75 mmHg. A blood oxygen level below 60 mmHg indicates a very severe blood deficiency and you need supplemental oxygen. The design of an oxygen saturation monitoring tool through the Thingspeak server with a max 30100 sensor based on nodemcu 8266 aims to make it easier to monitor oxygen levels in the blood so that it can take early anticipation to avoid unwanted things. The design of this tool is equipped with monitoring using a Thingspeak server that can be connected to the internet or WIFI so that we can do it when we are there. This blood tool is designed using a MAX 30100 sensor as an oxygen detector which is clamped on a finger and then connected to NodeMCU 8266. After waiting for a while the sensor detects oxygen levels &lt; 80% &gt;, 100% NodeMCU 8266 sends data to the LCD and Thingspeak. On the Thingspeak server we can observe the oxygen levels in our bodies. We can use this tool far away so we don't need to go to the hospital or health center to measure the oxygen saturation in our bodies.

SMART WRIST PULSE OXIMETER

In the present day we live in, a catastrophic virus COVID-19 has drastically changed the day to day living of a human being. The virus causes hypoxemia (shortness of breath), sometimes even severe cases. Hypoxemia is caused due to low oxygen saturation (SpO2) levels and in order to monitor SpO2 levels we utilize the method of Pulse Oximetry. It has played a major role in monitoring oxygen levels in a continuous and accurate manner. Patients who are diagnosed during the early stages with the virus are able to monitor their SpO2 levels at home and take the prescribed medicines. This reduced the need for hospital beds and chaos during the pandemic as patients were able to self-isolate and monitor themselves. The principle that Oximetry is contingent on is light reflectance. The fingertip model is the most common technique used to display the blood oxygenation level. However, the finger model is not as comfortable and does not promote continuous monitoring of SpO2 levels. Factors such as nail polish can play a role in the accuracy of the reading. The proposed design is a non-invasive medical device that can measure the oxygen saturation level in a person’s blood. Wrist wearing is preferrable to finger models as it is a comfortable site for measuring than that of the latter, therefore enabling continuous monitoring of oxygen saturation level. Most devices in application today are inaccurate and used for non-clinical use. Therefore, it is aimed to achieve better accuracy by avoiding readings that are influenced by factors such as motion artifacts by utilizing sensors that are appropriate through an accelerometer and gyroscope. The sensors have been utilized to its maximum potential as the model also detects heart rate levels. Providing device connectivity to the proposed wrist pulse oximeter through a Wi-Fi module has advanced its functionality by transmitting notifications that alert an individual with the levels of oxygen saturation, fall detection and heart rate levels.

Oxygen control: the often overlooked but essential piece to create better in vitro systems.

Variations in oxygen levels play key roles in numerous physiological and pathological processes, but are often not properly controlled in in vitro models, introducing a significant bias in experimental outcomes. Recent developments in microfluidic technology have introduced a paradigm shift by providing new opportunities to better mimic physiological and pathological conditions, which is achieved by both regulating and monitoring oxygen levels at the micrometre scale in miniaturized devices. In this review, we first introduce the nature and relevance of oxygen-dependent pathways in both physiological and pathological contexts. Subsequently, we discuss strategies to control oxygen in microfluidic devices, distinguishing between engineering approaches that operate at the device level during its fabrication and chemical approaches that involve the active perfusion of fluids oxygenated at a precise level or supplemented with oxygen-producing or oxygen-scavenging materials. In addition, we discuss readout approaches for monitoring oxygen levels at the cellular and tissue levels, focusing on electrochemical and optical detection schemes for high-resolution measurements directly on-chip. An overview of different applications in which microfluidic devices have been utilized to answer biological research questions is then provided. In the final section, we provide our vision for further technological refinements of oxygen-controlling devices and discuss how these devices can be employed to generate new fundamental insights regarding key scientific problems that call for emulating oxygen levels as encountered in vivo. We conclude by making the case that ultimately emulating physiological or pathological oxygen levels should become a standard feature in all in vitro cell, tissue, and organ models.

Effects of cool resistance exercise on oxygen metabolism in muscle tissue and clinical application

Resistance training is beneficial for elite athletes and the elderly, alike. It plays a key role in healthy ageing, helping retain muscle mass, and it can also help reduce the chances of chronic diseases such as osteoporosis and high blood pressure. In order for resistance exercise to be effective, there is an ongoing need for proven techniques that can assist with their resistance training. Professor Masahiro Goto, Director of the Department of Physical Therapy, Aino University, Japan, works to understand the physiological dynamics at play during resistance exercise with a view to developing novel exercise methods and using new technologies to improve resistance exercise outcomes. A brief intramuscular hypoxic state is key to promoting muscle growth and this has therefore been a target for improving resistance techniques, but a challenge arises in terms of monitoring hypoxia. That is why Goto is looking to establish a method that can accurately, quickly and cheaply test the intramuscular oxygenation state during resistance exercise. Recognising the potential of near infrared spectroscopy (NIRS), he performed a study on volunteers who have resistance exercise carrier more than one year over eight weeks to find out whether NIRS can be used as an effective measure of internal muscular oxygenation levels and if cold pack treatment of muscles prior to exercise results in better muscle mass gain. He used electromyograms to measure muscle contraction, ultrasound to monitor changes in muscle mass and arterial oxygen saturation measurements to elucidate oxygenation levels. He found that NIRS was effective for routine monitoring of oxygen levels and that cold pack treatment during resistance exercise causes higher muscle activity and creates a more hypoxic muscular environment than without any cold treatment.

160 Home Pulse Oximetry Monitoring for Patients With Suspected COVID-19: A Pilot Assessment of Patient Engagement and Compliance

Patients infected with SARS-CoV-2 who are evaluated in the emergency department but well enough to go home are still at risk for clinical deterioration. They may benefit from a program to monitor oxygen levels at home using portable pulse oximeter devices. Our study aims to evaluate patient engagement in and compliance with a home pulse oximetry monitoring program. The results of this study will be important to inform development and operationalization of remote patient monitoring programs.

Geospatial distribution of hypoxia associated with a Karenia brevis bloom

In 2018, the presence of bottom water hypoxia along the SW Florida coast was investigated during a bloom of the toxic dinoflagellate Karenia brevis. The bloom was first detected in November 2017. Monitoring of oxygen levels and bloom densities was carried out in 2018 and 2019 using sampling grids. Vertical profiles indicated a pycnocline at 3–4 m where warmer, lower salinity water was at the surface, while the deeper hypoxic layer was colder with higher salinity. There were significantly higher abundances of K. brevis in the surface water compared to the hypoxic bottom water in September 2018. At two fixed sites, dissolved oxygen was measured continuously showing hypoxic conditions during that month. Geospatial analysis of vertical profile data yielded an estimate that the hypoxic layer covered an area of at least 655 km2. The possible influences of red tides on hypoxic conditions along the coast of the eastern Gulf of Mexico are discussed within the context of the 2018 K. brevis bloom event. Hypoxia occurring in parallel to a red tide bloom is more likely to occur with warmer ocean temperatures and increased fluxes of nutrients and fresh water to the Gulf of Mexico after hurricanes.

COVID-19 mitigation measures to maintain access to essential health services: new opportunities with long-term benefits.

The coronavirus disease 2019 (COVID-19) pandemic has substantially impacted health systems globally. To highlight potential opportunities to improve health service delivery in low- and middle-income countries, we describe lessons learned from published literature and experiences responding to the pandemic. The benefits of healthcare service measures implemented during the pandemic with potential for lasting benefits for strengthening health systems are highlighted: 1) innovative pharmaceutical dispensing methods; 2) appointment-based systems in health facilities; 3) telehealth to provide patient care; 4) task shifting to redistribute healthcare workloads; and 5) home-based pulse oximetry to monitor oxygen levels. These measures can reduce unnecessary contact with healthcare staff while maintaining critical health service delivery and may be of value to continue after the pandemic subsides.

The Carotid Body a Common Denominator for Cardiovascular and Metabolic Dysfunction?

The carotid body is a highly vascularized organ designed to monitor oxygen levels. Reducing oxygen levels in blood results in increased activity of the carotid body cells and reflex increases in sympathetic nerve activity. A key contributor to elevated sympathetic nerve activity in neurogenic forms of hypertension is enhanced peripheral chemoreceptor activity. Hypertension commonly occurs in metabolic disorders, like obesity. Such metabolic diseases are serious global health problems. Yet, the mechanisms contributing to increased sympathetic nerve activity and hypertension in obesity are not fully understood and a better understanding is urgently required. In this review, we examine the literature that suggests that overactivity of the carotid body may also contribute to metabolic disturbances. The purine ATP is an important chemical mediator influencing the activity of the carotid body and the role of purines in the overactivity of the carotid body is explored. We will conclude with the suggestion that tonic overactivity of the carotid body may be a common denominator that contributes to the hypertension and metabolic dysfunction seen in conditions in which metabolic disease exists such as obesity or insulin resistance induced by high caloric intake. Therapeutic treatment targeting the carotid bodies may be a viable treatment since translation to the clinic could be more easily performed than expected via repurposing antagonists of purinergic receptors currently in clinical practice, and the use of other minimally invasive techniques that reduce the overactivity of the carotid bodies which may be developed for such clinical use.

Spatio-temporal variation of water quality variables and hydrography in a seabream cage culture farm off the coast of Oman

Mariculture cage farming in Oman is in its infancy stage. This study provides important baseline information about the initial state of mariculture in Oman and for the sustainable management of future local cage farming. Our main objective was to evaluate the spatio-temporal variations of water quality and hydrography around a gilthead seabream (Sparus aurata) cage farm in Quriyat (Sea of Oman). Starting in July 2018, we conducted a monitoring program over one year in which physico-chemical variables and nutrient levels were regularly measured at the farm cages and at reference sites away from the farm. Vertical flow profiles were recorded at the farm and analysed together with remotely sensed data. The results showed no significant differences among physico-chemical variables and nutrient levels between cages and reference sites. However, there were clear seasonal as well as significant short-term variations in the measurements. Winter conditions are usually homogeneous over the water column without reaching extremes. In summer we recorded surface temperatures of up to 32 °C and extended periods of hypoxia below 35 m depth. Periods of pronounced stratification were interrupted by energetic irregular flow pulses that triggered short up or down-welling events which lead to strong variations of temperature and oxygen. We did not measure a significant impact of the cage farm on the local environment. Our results rather point to the particular importance of monitoring temperature and oxygen levels. Both variables can approach threshold levels for fish farming, especially during summer. We determined the relevant characteristics of the local system and defined requirements for adequate monitoring. The findings of this study provide a timely baseline for future research on the interactions between local cage farms and the marine ecosystem and will assist in the planning and management of mariculture in Oman.

NON-INVASIVE BLOOD OXYGEN SATURATION MONITORING (SpO2) USING TRANSMITTANCE FOR PULSE OXIMETER

Measuring oxygen saturation of blood (SpO2) clinically plays a vital role in patient’s health monitoring. In fact, monitoring oxygen level is necessary for people having respiratory problems (pulmonary hypertension) and in other critical conditions. The primary motivation of this work is to develop a low cost computer-based oxygen saturation monitoring system using an embedded system along with lab windows CVI platform. The process of calculating the level of oxygen saturation in the blood using non-invasive method is also called as pulse oximetry, which consists of LED and photo detectors, using MSP430FG4618 microcontroller. The MSP430 employed in designing the microcontroller firmware program for digitization and transmission of the data from sensor to the computer. NI-based Lab windows/CVI Platform was developed as a part of this project to receive, plot, save data and determine the accuracy of SpO2 value. In this proposed system, we have achieved the maximum accuracy of 99.49% which is better than the previously developed methods. The proposed system is also designed with the low cost and low power consuming modules.

Monitoring Oxygen Levels within Large, Tissue-Engineered Constructs Using Porphyin-Hydrogel Microparticles.

A major barrier to the creation of engineered organs is the limited diffusion of oxygen through biological tissues. Advances in biofabrication bring us increasingly closer to complex vascular networks capable of supplying oxygen to large cellularized scaffolds. However, technologies for monitoring oxygen levels in engineered tissues do not accommodate imaging depths of more than a few dozen micrometers. Here, we report the creation of fluorescent porphyrin-hydrogel microparticles that can be used at depths of 2 mm into artificial tissues. By combining an oxygen-responsive porphyrin dye with a reference dye, the microparticles generate a ratiometric signal that is photostable, unaffected by attenuation from biological material, and responsive to physiological change in oxygen concentration. These microparticles can measure long-distance oxygen gradients within 3D, cellularized constructs and accurately report cellular oxygen consumption rates. Furthermore, they are compatible with a number of hydrogel polymerization chemistries and cell types, including primary human cells. We believe this technology will significantly advance efforts to visualize oxygen gradients in cellularized constructs and inform efforts to tissue engineer solid organs.

Vision is highly sensitive to oxygen availability in marine invertebrate larvae.

For many animals, evolution has selected for complex visual systems despite the high energetic demands associated with maintaining eyes and their processing structures. Therefore, the metabolic demands of visual systems make them highly sensitive to fluctuations in available oxygen. In the marine environment, oxygen changes over daily, seasonal and inter-annual time scales, and there are large gradients of oxygen with depth. Vision is linked to survival in many marine animals, particularly among the crustaceans, cephalopods and fish, and early life stages of these groups rely on vision for prey capture, predator detection and their distribution in the water column. Using in vivo electroretinogram recordings, we show that there is a decrease in retinal sensitivity to light in marine invertebrates when exposed to reduced oxygen availability. We found a 60-100% reduction in retinal responses in the larvae of cephalopods and crustaceans: the market squid (Doryteuthis opalescens), the two-spot octopus (Octopus bimaculatus), the tuna crab (Pleuroncodes planipes) and the graceful rock crab (Metacarcinus gracilis). A decline in oxygen also decreases the temporal resolution of vision in D. opalescens These results are the first demonstration that vision in marine invertebrates is highly sensitive to oxygen availability and that the thresholds for visual impairment from reduced oxygen are species-specific. Oxygen-impaired retinal function may change the visual behaviors crucial to survival in these marine larvae. These findings may impact our understanding of species' vulnerability to ocean oxygen loss and suggest that researchers conducting electrophysiology experiments should monitor oxygen levels, as even small changes in oxygen may affect the results.

Oxygen Monitoring Equipment for Sewage-Sludge Composting and Its Application to Aeration Optimization.

Oxygen is an important parameter for organic-waste composting, and continuous control of the oxygen in a composting pile may be beneficial. The oxygen consumption rate can be used to measure the degree of biological oxidation and decomposition of organic matter. However, without having a real-time online device to monitor oxygen levels in the composting pile, the adjustment and optimization of the composting process cannot be directly implemented. In the present study, we researched and developed such a system, and then tested its stability, reliability, and characteristics. The test results showed that the equipment was accurate and stable, and produced good responses with good repeatability. The equilibrium time required to detect oxygen concentration in the composting pile was 50 s, and the response time for oxygen detection was less than 2 s. The equipment could monitor oxygen concentration online and in real time to optimize the aeration strategy for the compost depending on the concentration indicated by the oxygen-measuring equipment.

Integrated phosphorescence-based photonic biosensor (iPOB) for monitoring oxygen levels in 3D cell culture systems

Physiological processes, such as respiration, circulation, digestion, and many pathologies alter oxygen concentration in the blood and tissue. When designing culture systems to recapitulate the in vivo oxygen environment, it is important to integrate systems for monitoring and controlling oxygen concentration. Herein, we report the design and engineering of a system to remotely monitor and control oxygen concentration inside a device for 3D cell culture. We integrate a photonic oxygen biosensor into the 3D tissue scaffold and regulate oxygen concentration via the control of purging gas flow. The integrated phosphorescence-based oxygen biosensor employs the quenching of palladium-benzoporphyrin by molecular oxygen to transduce the local oxygen concentration in the 3D tissue scaffold. The system is validated by testing the effects of normoxic and hypoxic culture conditions on healthy and tumorigenic breast epithelial cells, MCF-10A cells and BT474 cells, respectively. Under hypoxic conditions, both cell types exhibited upregulation of downstream target genes for the hypoxia marker gene, hypoxia-inducible factor 1α (HIF1A). Lastly, by monitoring the real-time fluctuation of oxygen concentration, we illustrated the formation of hypoxic culture conditions due to limited diffusion of oxygen through 3D tissue scaffolds.

Every Breath You Take: Non-invasive Real-Time Oxygen Biosensing in Two- and Three-Dimensional Microfluidic Cell Models.

Knowledge on the availability of dissolved oxygen inside microfluidic cell culture systems is vital for recreating physiological-relevant microenvironments and for providing reliable and reproducible measurement conditions. It is important to highlight that in vivo cells experience a diverse range of oxygen tensions depending on the resident tissue type, which can also be recreated in vitro using specialized cell culture instruments that regulate external oxygen concentrations. While cell-culture conditions can be readily adjusted using state-of-the-art incubators, the control of physiological-relevant microenvironments within the microfluidic chip, however, requires the integration of oxygen sensors. Although several sensing approaches have been reported to monitor oxygen levels in the presence of cell monolayers, oxygen demands of microfluidic three-dimensional (3D)-cell cultures and spatio-temporal variations of oxygen concentrations inside two-dimensional (2D) and 3D cell culture systems are still largely unknown. To gain a better understanding on available oxygen levels inside organ-on-a-chip systems, we have therefore developed two different microfluidic devices containing embedded sensor arrays to monitor local oxygen levels to investigate (i) oxygen consumption rates of 2D and 3D hydrogel-based cell cultures, (ii) the establishment of oxygen gradients within cell culture chambers, and (iii) influence of microfluidic material (e.g., gas tight vs. gas permeable), surface coatings, cell densities, and medium flow rate on the respiratory activities of four different cell types. We demonstrate how dynamic control of cyclic normoxic-hypoxic cell microenvironments can be readily accomplished using programmable flow profiles employing both gas-impermeable and gas-permeable microfluidic biochips.

Tissue Oxygenation within Diabetic Wounds can be Monitored Using Difluoroboron β– Diketonate Polylactide Nanoparticles

OBJECTIVERoughly 6.5 million diabetic patients in the United States suffer from chronic wounds that exhibit impaired healing response1. These wounds often do not respond to standard treatment due to insufficient oxygenation in the wound bed2. Given the heterogeneity of oxygen levels in wounds and the importance of oxygen in tissue repair, it is compelling to develop a reliable way to non‐invasively monitor oxygen levels within chronic wounds over time. Previously, we demonstrated the ability of topically‐delivered BF2nbm(I)PLA boron dye nanoparticles (BNPs) that phosphoresce differentially at varying oxygen levels, to provide a spatial map of oxygen levels throughout the wound bed of a murine full‐thickness cutaneous wound3. The objective of this work is to validate the ability of BNP imaging to detect impaired tissue oxygenation during wound healing in diabetic individuals compared to healthy individuals.METHODSWe have developed a novel model of wound healing in the murine ear which allows measurements of oxygen levels in both tissue and blood vessels using BNP imaging and photoacoustic microscopy (PAM), respectively. PAM non‐invasively measures structural and hemodynamic changes, including vessel diameter, hemoglobin concentration, blood flow speed, and hemoglobin oxygen saturation levels in individual blood vessels down to the capillary level during microvascular remodeling within wound beds4. In this ear wound model, the epidermis and a portion of the dermis, including the center feeder arteriole and its main branches, are excised from the center of the ear lobe. The wound is covered with Tegaderm bandage to prevent drying, and the mouse is fitted with an Elizabethan collar to prevent it from removing the bandage. At regular intervals until the wound heals, BNPs are topically applied to the wound and excited by UV light for two minutes during which the fluorescence (F) and phosphorescence (P) emission signals are recorded using a camera. A custom Matlab program calculates the ratio of F:P emission intensities at each pixel in the wound bed image, which provides a relative mapping of oxygen levels throughout the wound. Following BNP imaging, PAM imaging is performed in order to calculate the percent sO2 in each blood vessel in/around the wound bed. BNP and PAM measurements are compared to one another for wounds in both healthy and diabetic mice.RESULTSDiabetic db/db mice exhibit muted wound oxygenation increases over time compared to non‐diabetic control mice. BNP fluorescence:phosphorescence emission ratios from wound beds emulate sO2 trends generated via PAM, confirming the ability of BNPs to assess tissue oxygenation over time in both diabetic and healthy wounds.CONCLUSIONSBNPs can be used to monitor tissue oxygenation over time in diabetic and healthy wounds. Given their low cost and potential for clinical monitoring of these wounds in humans, BNPs warrant further study for non‐invasively monitoring wound healing over time.Support or Funding InformationUVA School of Medicine Pinn Scholars ProgramThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pre-clinical evaluation of OxyChip for long-term EPR oximetry.

Tissue oxygenation is a critical parameter in various pathophysiological situations including cardiovascular disease and cancer. Hypoxia can significantly influence the prognosis of solid malignancies and the efficacy of their treatment by radiation or chemotherapy. Electron paramagnetic resonance (EPR) oximetry is a reliable method for repeatedly assessing and monitoring oxygen levels in tissues. Lithium octa-n-butoxynaphthalocyanine (LiNc-BuO) has been developed as a probe for biological EPR oximetry, especially for clinical use. However, clinical applicability of LiNc-BuO crystals is hampered by potential limitations associated with biocompatibility, biodegradation, ormigration of individual bare crystals in tissue. To overcome these limitations, we have embedded LiNc-BuO crystals in polydimethylsiloxane (PDMS), an oxygen-permeable biocompatible polymer and developed an implantable/retrievable form of chip, called OxyChip. The chip was optimized for maximum spin density (40% w/w of LiNc-BuO in PDMS) and fabricated in a form suitable for implantation using an 18-G syringe needle. In vitro evaluation of the OxyChip showed that it is robust and highly oxygen sensitive. The dependence of its EPR linewidth to oxygen was linear and highly reproducible. In vivo efficacy of the OxyChip was evaluated by implanting it in rat femoris muscle and following its response to tissue oxygenation for up to 12months. The results revealed preservation of the integrity (size and shape) and calibration (oxygen sensitivity) of the OxyChip throughout the implantation period. Further, no inflammatory or adverse reaction around the implantation area was observed thereby establishing its biocompatibility and safety. Overall, the results demonstrated that the newly-fabricated high-sensitive OxyChip is capable of providing long-term measurements of oxygen concentration in a reliable and repeated manner under clinical conditions.

A Breath of Fresh Air: A Genetically Encoded O2 Probe for Direct Mapping and Quantification of Oxygenation Levels in Cells via Fluorescence Lifetime Imaging

Molecular oxygen is an important reporter of metabolic and physiological status at the cellular and tissue level, and its concentration can be used for the evaluation of diseases of various nature (e.g.: cancer, coronary artery disease). The development of accurate and quantitative methods to measure O2 concentration in living cells, tissues and organisms has remained challenging and is subject of intense research. We developed a protein-based, fluorescent oxygen sensor that can be expressed directly in cells to monitor oxygen levels in the cytoplasmic environment. We fused Myoglobin (Mb), a physiological oxygen carrier, with mCherry, a fluorescent protein, to build a fluorescence resonance energy transfer (FRET) pair where Myoglobin acts as a variable dark acceptor. The changes in the spectral properties of Myoglobin upon oxygen binding translate into changes of the FRET-depleted emission intensity of mCherry, and this effect is best detected by monitoring the fluorescence lifetime of the probe. We present in this work the expression and characterization of the Mb-mCherry system in vitro to establish a calibration curve of its response to [O2] and other relevant effectors. Further, by using Fluorescence Lifetime Imaging Microscopy (FLIM), we show that we are able to map the oxygenation level of the probe ex vivo in cells, providing a quantitative description. A genetically encoded oxygen probe based on fluorescence addresses the most common issues with currently available methods to monitor O2 levels in living organisms: data collection speed, spatial resolution and localization within cells and tissues. Customization of the response can be achieved by exploiting the mutations of Mb to tune O2 binding affinity, or the response to external modulators (e.g.: lactate) present in the cell.