Measurement Of Oxygen Concentration Research Articles

Evaluation and optimization of the performance characteristics of fast response fiber optic oxygen gas probes

Even though many different designs for currently available, fluorescence-based fiber optic sensors for measuring oxygen concentration (O2) are well known (and indeed some are commercially available), they often are limited by their response time and long-term stability. This will cause problems in the important industrial applications of fiber optic sensors of this type that are developing, with limitations that are evident, for example, in physiology and other fields where rapid sensor responses are required. Research by a number of groups has discussed various new designs of fiber optical sensors, which have been developed in recent years where the key features of such probes to achieve the performance required are, for example, optimization of design features such as tip shape and coating layer thickness. The research reported in this paper represents an evaluation of such key factors to allow the design of better fiber optic-based sensors for oxygen measurement, where the optimized performance of a new, specially tapered tip O2 sensor designed has been compared with the output of conventional and commercially available probe designs. The performance of a group of such sensors has been analyzed and cross-compared, examining the key features of such a probe including sensor accuracy, response time and overall long-term stability, as well as cross-sensitivity to any temperature changes which may occur in ‘real’ measurement situations.

Surface oxygen concentration on the Qinghai-Tibet Plateau (2017–2022)

For the ecologically vulnerable Qinghai-Tibet Plateau (QTP), hypoxia is increasingly becoming an extremely important environmental risk factor that significantly affects the health of both humans and livestock in the plateau region, as well as hindering high-quality development. To focus on the problem of hypoxia, it is especially urgent to study the surface oxygen concentration (i.e., oxygen concentration). However, the existing research is not sufficient, and there is a lack of oxygen concentration data collected on the QTP. In this study, through the Second Tibetan Plateau Scientific Expedition and Research and field measurements, the oxygen concentration data and corresponding geographic environmental data were collected at 807 measurement points on the QTP from 2017 to 2022, and the spatiotemporal oxygen concentration patterns were estimated. This work filled the gaps in the measurement and research of oxygen concentrations on the QTP while providing data support for analyses of the influencing factors and spatiotemporal characteristics of oxygen concentrations, which is of great significance for promoting the construction of ecological civilization in the QTP region.

A feasible heat release rate estimation approach for fire hazard assessment in green design

New energy harvesting systems in buildings are becoming more attractive in new green buildings. However, the potential fire hazard of the combustible items used in new green building limits their wider application. Fire behaviour of combustible items in new green designs should be studied carefully. Heat release rate of burning combustible items of different materials is important in fire hazard assessment and can be estimated by oxygen consumption calorimetry. An exhaust hood with a fan-duct system was built to collect flue gas. As the burning was likely to be incomplete in building fires, carbon monoxide, carbon dioxide, water vapor and soot would be emitted. Heat release rates of combustible items were estimated by measuring the transient amount of oxygen, carbon monoxide and carbon dioxide collected by the hood. Based on mass balancing, there are at least three equations in terms of mass flow rates of oxygen, carbon monoxide and carbon dioxide in the incoming air and exhaust gas. There are always questions about using which equations because measuring gases in full-scale burning tests is difficult and expensive. These three equations are introduced and compared in this paper. Heat release rates of four selected combustible items were studied as an example case. Accuracy of the results based on the measured oxygen concentration only was similar to the values provided by commercial software. Results from the experimental data are useful in further full-scale burning tests on combustible items in energy harvest systems planning at the moment.

Evaluation of Usefulness of Yeast-Based Biological Phantom and Preliminary Study for Verification of Hypoxic Effect of Flash Radiotherapy

As a basic hypothesis for the effectiveness of flash radiation therapy, the effect of preserving normal tissue during flash radiation is due to the instantaneous chemical depletion of oxygen. A yeast-based biological phantom was created to verify the hypoxic effect of flash radiation therapy. A study to upgrade the previously developed X-Band LINAC to a flash irradiation mode is in progress, and a preceding study is conducted to evaluate the usefulness of a yeast-based biological phantom manufactured by analyzing the change in oxygen by irradiating a high dose in a general radiation therapy device. Freeze-dried yeast sample (Saccharomyces cerevisiae, S288C) is activated and sub-cultured. For mass production of yeast samples, yeast culture medium is prepared by adding yeast colonies to the ypd medium. This study was conducted to verify the hypoxic effect among the biological mechanisms that occur during flash radiation therapy at the basic stage, and the oxygen concentration change during general radiation irradiation was measured in real time using a DO (Dissolved oxygen) meter and fiber optic sensor designed to do that. To prevent scatter, which is a concern during flash irradiation, the fiber form was used, and precise experiments are possible as a non-invasive oxygen concentration measurement method. Based on 10MV of general radiation therapy device, high-dose radiation of 500-10,000 cGy is irradiated to measure real-time oxygen concentration change. As a result of irradiation with high-dose (500-10,000 cGy) radiation of general LINAC, it was confirmed that the oxygen concentration of the yeast culture medium decreased by 5.7-63.2%, and the usefulness of the biological phantom fabricated based on the yeast culture medium was evaluated. Prior to the analysis of oxygen concentration change in yeast cells during X-Band LINAC flash irradiation, a preliminary study was conducted at a high dose in a general LINAC to obtain a significant result of oxygen concentration change and confirm the usefulness of the yeast-based biological phantom. Prior research was conducted and verified as a general irradiation experiment using a yeast-based biological phantom manufactured based on a DO meter and a fiber optic oxygen sensor. After irradiation with high-dose radiation, the oxygen concentration of the yeast culture medium was measured 5 times, and it was confirmed that there was a change in oxygen concentration of 5.7-63.2%, verifying the usefulness and stability of the biological phantom. The usefulness of the yeast-based biological phantom for high doses was confirmed, and it is expected that the usefulness of the biological phantom for flash radiation can be verified by additionally measuring the change in oxygen concentration of the biological phantom according to the high dose rate in the future.

The metabolic response of human trophoblasts derived from term placentas to metformin

Aims/hypothesisMetformin is increasingly used therapeutically during pregnancy worldwide, particularly in the treatment of gestational diabetes, which affects a substantial proportion of pregnant women globally. However, the impact on placental metabolism remains unclear. In view of the association between metformin use in pregnancy and decreased birthweight, it is essential to understand how metformin modulates the bioenergetic and anabolic functions of the placenta.MethodsA cohort of 55 placentas delivered by elective Caesarean section at term was collected from consenting participants. Trophoblasts were isolated from the placental samples and treated in vitro with clinically relevant doses of metformin (0.01 mmol/l or 0.1 mmol/l) or vehicle. Respiratory function was assayed using high-resolution respirometry to measure oxygen concentration and calculated {dot{V}mathrm{O}}_{2}. Glycolytic rate and glycolytic stress assays were performed using Agilent Seahorse XF assays. Fatty acid uptake and oxidation measurements were conducted using radioisotope-labelled assays. Lipidomic analysis was conducted using LC-MS. Gene expression and protein analysis were performed using RT-PCR and western blotting, respectively.ResultsComplex I-supported oxidative phosphorylation was lower in metformin-treated trophoblasts (0.01 mmol/l metformin, 61.7% of control, p<0.05; 0.1 mmol/l metformin, 43.1% of control, p<0.001). The proton efflux rate arising from glycolysis under physiological conditions was increased following metformin treatment, up to 23±5% above control conditions following treatment with 0.1 mmol/l metformin (p<0.01). There was a significant increase in triglyceride concentrations in trophoblasts treated with 0.1 mmol/l metformin (p<0.05), particularly those of esters of long-chain polyunsaturated fatty acids. Fatty acid oxidation was reduced by ~50% in trophoblasts treated with 0.1 mmol/l metformin compared with controls (p<0.001), with no difference in uptake between treatment groups.Conclusions/interpretationIn primary trophoblasts derived from term placentas metformin treatment caused a reduction in oxidative phosphorylation through partial inactivation of complex I and potentially by other mechanisms. Metformin-treated trophoblasts accumulate lipids, particularly long- and very-long-chain polyunsaturated fatty acids. Our findings raise clinically important questions about the balance of risk of metformin use during pregnancy, particularly in situations where the benefits are not clear-cut and alternative therapies are available.Graphical

Three-dimensional oxygen concentration monitoring in hydrogels using low-cost phosphorescence lifetime imaging for tissue engineering.

Oxygen concentration measurement in 3D hydrogels is vital in 3D cell culture and tissue engineering. However, standard 3D imaging systems capable of measuring oxygen concentration with adequate precision are based on advanced microscopy platforms, which are not accessible in many laboratories due to the system's complexity and the high price. In this work, we present a fast and low-cost phosphorescence lifetime imaging design for measuring the lifetime of oxygen-quenched phosphorescence emission with 0.25 µs temporal precision and sub-millimeter spatial resolution in 3D. By combining light-sheet illumination and the frequency-domain lifetime measurement using a commercial rolling-shutter CMOS camera in the structure of a conventional optical microscope, this design is highly customizable to accommodate application-specific research needs while also being low-cost as compared to advanced instruments. As a demonstration, we made a fluidic device with a gas-permeable film to create an artificial oxygen gradient in the hydrogel sample. Dye-embedded beads were distributed in the hydrogel to conduct continuous emission lifetime monitoring when nitrogen was pumped through the fluidic channel and changed oxygen distribution in the sample. The dynamics of the changes in lifetime co-related with their location in the gel of size 0.5 mm×1.5 mm×700 µm demonstrate the ability of this design to measure the oxygen concentration stably and precisely in 3D samples.

Development of Monitoring Parameters of Oxygen Concentration, Oxygen Flow Rate, Temperature and Humidity in IoT-Based CPAP Bubble (Oxygen and Humidity Concentration)

Bubble Continuous Positive Airway Pressure (CPAP) is a device to maintain positive pressure in the neonate's airway as long as it can breathe spontaneously. FiO2 percentage, flowmeter, humidifier mode, PEEP depth are parameters that must be set for oxygen therapy using a cpap bubble device, but this tool has minimal monitoring. It has been developed by several previous researchers but has several shortcomings, namely there is no digital result display, no measurement of oxygen rate, oxygen concentration, temperature and humidity. The purpose of this research is to design a parameter monitoring tool on the cpap bubble so that it can monitor the baby's condition in real time and can be used as an indicator of achieving the desired concentration setting. The contribution in this study is a monitoring system or remote monitoring so that nurses and doctors can monitor the baby's condition even though they are not accompanying him. In order to facilitate the process of monitoring and diagnosing patients, a parameter monitoring tool on the cpap bubble based on the Internet of Things is made with notifications on telegrams so that patients can be treated quickly. The design of this tool uses OCS-3f as a sensor for detecting oxygen concentration and DHT22 as a sensor for detecting humidity. The output of oxygen and humidity concentrations is then processed by the ESP32 microcontroller into the ADC pin. Data that has been processed from analog sensor data into digital data on the ESP32 is then sent to the https://thinger.io site using the internet network via the wifi module contained in the ESP32 module build-in. In measuring positioned in the settings of 21% to 95%. The largest error value obtained is 4.6% and the smallest is 0.04%.

Artificial Circulation Effect on Oxygen Saturation in the Brain Phantom

Cardiovascular surgery represents a field where the anesthetist frequently deals with quickly evolving conditions associated with anesthesia, perfusion, and the scope of surgery, that have a direct and indirect impact on the oxygen delivery to organs and tissues and its consumption ratio. The prospects of predicting the oxygen concentration influential factors on the brain create a possibility for effective decisions in the crucial moments of cardiac surgery during a cardiopulmonary bypass, to choose specific neuroprotection to decrease postoperative neurologic complication risk. Nowadays, near-infrared spectroscopy (NIRS) technology has been used to perform cerebral oximetry analysis. By reviewing available literature, the work on the possible dependence of artificial blood circulation on oxygen concentration in the brain is provided. This research aims to investigate how artificial circulation, specifically the flow and viscosity of the fluid equivalent to blood, affects oxygen concentration in the cerebral phantom. The thesis contains methodology for measuring the concentration of oxygen was considered, as well as the manufacture of a phantom of the brain and an equivalent blood fluid. The results illustrate that the artificial blood flow rate has a non-linear effect on the oxygen concentration in the brain phantom. This was confirmed through the value of the oxygen concentration in the brain phantom under conditions of artificial blood circulation rSO_2avg.= 85% with laminar flow and the value of rSO_2avg.= 78% with turbulent flow. Additionally, it was proven that as the viscosity of the blood-equivalent fluid increases, the oxygen concentration decreases almost linearly. The calculated average rSO₂ value at minimum viscosity η=2.0 mPa∙s and flow rate Q=0.5 l/min has maximum rSO_2avg.=85%, while at maximum viscosity η=4.2 mPa∙s, rSO₂ average value was the smallest rSO_2avg.=72%. The study demonstrates that the type and rate of flow, as well as viscosity of the cardiopulmonary bypass, affect the measurements of oxygen concentration in the brain phantom.

Design and realization of a mobile-automatic calibration system for ventilator testers: oxygen concentration

Ventilators have a vital role in supplying oxygen to the patients experiencing respiratory failure and ensuring the patient’s oxygen saturation to levels above 50% continuously. Therefore, the accuracy of oxygen concentration measurement becomes very important to assure patient safety obtained by testing the ventilator against a ventilator tester. Testing and calibration laboratory use a ventilator tester for routine calibration of health facilities as well as performance and clinical testing for emergency ventilators that developed massively these days. A mobile-ventilator tester calibration system for oxygen levels, especially for concentrations of 30%, 60%, and 90% according to SNI ISO 80601-2-12:2020, is being developed. This calibration system is designed to operate automatically based on Laboratory virtual instruments engineering workbench (LabVIEW) to control the instrumentation system and perform data acquisition of (oxygen concentration) readings. Three concentrations of oxygen gas reference are stored each on 2 L gas reservoirs to ease the mobilization of the system to testing and calibration laboratory. Hopefully, the traceability to International System of Units (SI) for the ventilator tester can be realized with this calibration system, thus can improve the quality of health services and increase the competitiveness of nationally produced medical devices. Although some improvements are required, the prototype of the calibrator works appropriately as intended.

Development and measurement of airborne oxygen sensor for aircraft inerting system based on TDLAS with pressure compensation and 2f/1f normalized method

Using Tunable Diode Laser Absorption Spectroscopy (TDLAS）technology to accurately measure the oxygen concentration in the ullage of the aircraft fuel tank is of great significance to ensure the safety of the aircraft and improve the working quality of the aircraft onboard inerting system. This paper focuses on designing a smart sensor for the detection of oxygen concentration applied to airborne inerting systems, which can reduce random environmental noise and lineshape errors during the flying process. First, a prototypeincluding a laser emission module with wavelength modulation and temperature control, a multi-reflection long optical path absorption gas cell, and a high-precision signal extraction module are designed. Then, ground experiments at 294 K, and 1 bar are carried out. The oxygen inversion method is designed, the oxygen concentration results are obtained, and the lower detection limit (3.3 ppm) and detection accuracy (9.6 ppm) of the sensor are discussed. Thirdly, the change of absorption line profile influenced by the change of pressure is discussed. The series of oxygen concentration measurement experiments with variable pressure (274 k, 1–0.1 bar) was carried out. and the measurement error is below 1%. Finally, a second harmonic (2f)/first harmonic (1f) normalized method is proposed to eliminate the errors caused by laser attenuation and environmental vibration in oxygen measurement.

Abstract 190: Personalized identification of cancer treatments in real-time: TumOC - a tumor organoid-on-chip platform for online cell vitality measurements

Abstract Enhanced, physiologically relevant in-vitro tumor models significantly increase the success rate in new drug development, reduce the number of animal experiments and result finally in better therapies for cancer patients. Furthermore, they have the potential to offer new approaches to personalized oncology. In recent years, 3D cell cultures were established as relevant preclinical cancer models, suitable for high-throughput-screening. However, their capacity to model and/or measure physiological processes can still be enhanced. Colorectal carcinomas (CRC) are one of the most common malignant tumors. Due to its heterogeneity and high probability to metastasize, the disease is often incurable and novel, improved therapies are urgently needed. In this project, we developed a tumor organoid-on-chip platform (TumOC) by combining most recent technological advances: We integrated CRC patient-derived 3D cell cultures (organoids) and microsensor particles that enable assessment of cell vitality in real time by measuring oxygen concentration in a microfluidic system. The resulting TumOC platform allows for defined exposition of cytostatic drugs including dynamic and combination treatments. Measurements of cell vitality in real time enables analysis of not only the final effect of a drug treatment, but also the kinetics of drug response. At the same time, utilizing organoids allows for recapitulating tumor architecture and heterogeneity. Using the TumOC platform, we measured the cell vitality in real time over several days during treatment with classic chemotherapeutics or targeted cancer drugs and compared the results to end-point measurements on the same organoids in a static system. We assessed the effect of intra- and intertumoral heterogeneity and developed a protocol for treatment with clinically used combination regimes. In conclusion, our TumOC platform with its ability to recapitulate tumor heterogeneity in combination with dynamic treatments and real-time cell vitality assessment is an in-vitro tumor model closely recapitulating the physiological situation in a patient. TumOC provides an impressive opportunity to test and, consequently, predict the effectiveness of anti-cancer therapies. Therefore, this system is of interest not only for pre-clinical drug development but also for personalized oncology. Citation Format: Marie Flechner, Juergen Loskutov, Madeleine Nadolny, Ulrike Pfohl, Christian R. Regenbrecht, Katja Uhlig, Lena Wedeken. Personalized identification of cancer treatments in real-time: TumOC - a tumor organoid-on-chip platform for online cell vitality measurements [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 190.

TS-LSSVM: Triple sparse least squares support vector machine for residual oxygen concentration detection of encapsulated pharmaceutical vials

Accurate measurement of residual oxygen concentration in encapsulated pharmaceutical vials is adequate to ensure the quality of inner sterile preparations. However, the critical characteristic signal is feeble and covered by enormous environmental interference in the actual production. Inspired by structural sparse learning, we propose a novel prediction model in this paper, triple sparse least squares support vector machine (TS-LSSVM), in which the production priors are deeply excavated, and the feature, sample, and structure sparsity are realized simultaneously by redefining the objective function. In addition, the selection of support vectors can be adjusted adaptively according to the time-varying environmental noise, so as to ensure the reliability of long-term operation. First, the time–frequency components containing the prior knowledge are extracted based on the synchro squeezing wavelet transform (SSWT). Then, a triple sparse learning strategy is designed, which can accurately eliminate redundant wavelet coefficients and adaptively select training samples. Finally, a strict and fast optimization solution is proposed under the alternating direction method of multipliers (ADMM) framework. Experimental results on public and practical datasets prove the superiority of TS-LSSVM.

Measurement of oxygen concentration in atmospheric air using ultrasound time of flight with humidity compensation.

An absolute gas concentration can be measured from the variation in the speed of sound between two gases in principle. Owing to the small difference in the speed of sound between the atmospheric air and oxygen (O2) gas, measuring O2 concentration with high accuracy in the humid atmospheric air using ultrasound needs careful investigation. The authors show successfully a method to measure the absolute concentration of O2 gas in humid atmospheric air using ultrasound. It was possible to measure O2 concentration in the atmospheric air with accuracy by compensating for the influence of temperature and humidity by calculation. The O2 concentration was calculated from the conventional speed of sound equation by utilizing small mass variation for the change in moisture as well as temperature. This method using ultrasound enabled us to measure the O2 concentration in the atmospheric air as 21.0%, which is in agreement with the standard atmospheric dry air. The measurement error values after the humidity compensation are about 0.4% or less. Furthermore, this method takes only about a few ms for measuring O2 concentration and, thus, can be used as a high-speed portable O2 sensor for industrial, environmental, and biomedical instruments.

The Development of a Novel Headspace O2 Concentration Measurement Sensor for Vials.

In the process of manufacture and transportation, vials are prone to breakage and cracks. Oxygen (O2) in the air entering vials can lead to the deterioration of medicine and a reduction in pesticide effects, threatening the life of patients. Therefore, accurate measurement of the headspace O2 concentration for vials is crucial to ensure pharmaceutical quality. In this invited paper, a novel headspace oxygen concentration measurement (HOCM) sensor for vials was developed based on tunable diode laser absorption spectroscopy (TDLAS). First, a long-optical-path multi-pass cell was designed by optimizing the original system. Moreover, vials with different O2 concentrations (0%, 5%, 10%, 15%, 20%, and 25%) were measured with this optimized system in order to study the relationship between the leakage coefficient and O2 concentration; the root mean square error of the fitting was 0.13. Moreover, the measurement accuracy indicates that the novel HOCM sensor achieved an average percentage error of 1.9%. Sealed vials with different leakage holes (4, 6, 8, and 10 mm) were prepared to investigate the variation in the headspace O2 concentration with time. The results show that the novel HOCM sensor is non-invasive and has a fast response and high accuracy, with prospects in applications for online quality supervision and management of production lines.

Effect of Partial Equilibrium and Redox Reactions in a Zirconia Solid Electrolyte on the Electromotive Force in a Zirconia Oxygen Sensor

A zirconia oxygen sensor is an electrochemical device for rapidly measuring oxygen concentrations in molten metals at high temperatures. It is desirable to make the sensors capable of continuous, long-time measurements. Here, the effect on the electromotive force of a partial equilibrium state on the surface of a zirconia solid electrolyte in a zirconia oxygen sensor was investigated to reveal the factors preventing long-time measurements. The reference electrode was a mixture of W and WO2. Continuous measurements were performed in molten iron containing carbon for deoxidization. The electromotive force between the positive reference electrode and the negative sample electrode of the sensor decreased from a positive value to zero over time. This was because a metallic tungsten layer formed on the surface of the zirconia electrolyte by the reduction of the tungsten oxide via oxygen diffusion through the zirconia tube. In addition, the equilibrium in the reference electrode was disturbed during the measurements. A direct electrical current was applied to the sensor to examine the relationship between the surface and measured values. The electromotive force during the current was maintained at a higher value than that without the current because of induced re-oxidation at the zirconia surface. However, a long-time application could cause over-oxidation and dissolution of the reference electrode surface.

Study of some physical and chemical properties of drinking water in Samarra city and comparing with mineral water

This study was conducted in the city of Samarra on different samples of Samarra liquefaction and liquefaction of (S.D.I) and some mineral water samples of the most popular markets in the city, such as (nada water and alain water).&#x0D; During the study, some physical and chemical properties examination of the samples studied, such as turbidity and conductivity and the amount of soluble salts have also been some chemical properties such as the concentration of chlorine and oxygen concentration and pH measurement function.&#x0D; The study shown in the sample liquefaction of (S.D.I) is worst properties like turbidity standards and the concentration of oxygen and chlorine but they were complying in each of the pH and conductivity and the concentration of soluble salts function associated with raw water source, a river water (the Tigris River).&#x0D; It came in second place of the poor quality of water Specifications liquefaction Samarra while bottled water showed good readings of the properties studied.

Impact of Bi content on the accuracy of oxygen concentration measurements in liquid Pb–Bi alloys

Accurate measurements of the oxygen concentration in liquid lead-bismuth eutectic (LBE) alloys are essential for ensuring optimum cooling conditions in heavy liquid metal coolant fast reactors. However, while unavoidable variations in the Bi contents of these alloys can affect the accuracy of these measurements, this issue has not yet been rigorously evaluated. The present work addresses this issue by evaluating variations in oxygen concentration measurements obtained experimentally for oxygen-saturated liquid LBE alloys with different Bi contents at different temperatures using a solid electrolyte oxygen sensor. Theoretical relationships are established between sensor voltage, oxygen concentration, temperature, and Bi content under the applied experimental conditions, and excellent agreement is obtained between the experimental and theoretical results. The theoretical relationships establish that the voltage decreases by about 1 mV for every 1 wt% increase in Bi content at a temperature of 400 °C. At a fixed voltage, with the increase of T, the influence of the Bi content on the CO calculation results gradually increased. Finally, the impact of varying Bi contents on the accuracy of oxygen concentration measurements is evaluated under practical reactor operation conditions, and higher requirements for the control of dissolved oxygen in LBE-cooled fast reactors are proposed.

Assessing In Vivo Oxygen Dynamics Using Plant N-Terminal Degrons in Saccharomyces cerevisiae.

The expression of plant cysteine oxidase (PCO) enzyme in Saccharomyces cerevisiae enables the Arg/Cys N-degron pathway (Cys-NDP) for selective protein degradation that, in plants, functions as direct oxygen perception mechanism. A synthetic construct based on the plant Cys-NDP substrate related to apetala 2.12 (RAP2.12), the dual luciferase oxygen reporter (DLOR), exploits the N-terminal Cys of RAP2.12, and its oxygen-dependent degradation through the Cys-NDP. The luminescent output of DLOR can be used as a proxy for intracellular oxygen dynamics in budding yeast. Replacement of the luciferase reporter of the DLOR with fluorescent proteins would furthermore facilitate the imaging of reporter dynamics in living cells. In this chapter, we describe the methods for delivering the DLOR synthetic construct to yeast and calibrating its output by means of oxygen quantification in the culture with a physical oxygen sensor. We explain the setup needed to carry out hypoxic treatments with several colonies as replicates. We also describe the method to measure oxygen concentration in the culture, the closest indication of intracellular oxygen levels, as a way that would serve to calibrate the DLOR output. Finally, we propose a strategy to replace the luminescent reporters in the DLOR with fluorescent proteins to visualize oxygen dynamics in vivo.

Direct measurement of the aerotactic response in a bacterial suspension.

Aerotaxis is the ability of motile cells to navigate toward oxygen. A key question is the dependence of the aerotactic velocity with the local oxygen concentration c. Here we combine simultaneous bacteria tracking and local oxygen concentration measurements using Ruthenium encapsulated in micelles to characterize the aerotactic response of Burkholderia contaminans, a motile bacterium ubiquitous in the environment. In our experiments, an oxygen gradient is produced by the bacterial respiration in a sealed glass capillary permeable to oxygen at one end, producing a bacterial band traveling toward the oxygen source. We compute the aerotactic response χ(c) both at the population scale, from the drift velocity in the bacterial band, and at the bacterial scale, from the angular modulation of the run times. Both methods are consistent with a power-law χ∝c^{-2}, in good agreement with existing models based on the biochemistry of bacterial membrane receptors.

Sensors in a Flash! Oxygen Nanosensors for Microbial Metabolic Monitoring Synthesized by Flash Nanoprecipitation.

Flash nanoprecipitation (FNP) is an efficient and scalable nanoparticle synthesis method that has not previously been applied to nanosensor fabrication. Current nanosensor fabrication methods have traditionally exhibited poor replicability and consistency resulting in high batch-to-batch variability, highlighting the need for a more tunable and efficient method such as FNP. We used FNP to fabricate nanosensors to sense oxygen based on an oxygen-sensitive dye and a reference dye, as a tool for measuring microbial metabolism. We used fluorescence spectroscopy to optimize nanosensor formulations, calibrate the nanosensors for oxygen concentration determination, and measure oxygen concentrations through oxygen-sensitive dye luminescence. FNP provides an effective platform for making sensors capable of responding to oxygen concentration in gas-bubbled solutions as well as in microbial environments. The environments we tested the sensors in arePseudomonas aeruginosa biofilms andSaccharomyces cerevisiae liquid cultures—both settings where oxygen concentration is highly dependent on microbial activity. With FNP now applied to nanosensor fabrication, future nanosensor applications can take advantage of improved product quality through better replicability and consistency while maintaining the original function of the nanosensor.