Oxygen Sensor Research Articles

Tailoring the Electrocatalytic Properties of Porphyrin Covalent Organic Frameworks for Highly Selective Oxygen Sensing In Vivo.

In vivo selective sensing of oxygen (O2) dynamics in the central nervous system could provide insights into energy metabolism and neural activities. Although the electrocatalytic four-electron oxygen reduction reaction (ORR) paves an effective way to the electrochemical sensing of O2 in vivo, the concurrent hydrogen peroxide reduction reaction (HPRR) within the potential windows for four-electron ORR unfortunately poses a great challenge to the conventional mechanism employed for selective electrochemical O2 sensing. In this work, we find that regulation of the linkers within the skeleton of porphyrin-based covalent organic frameworks (COFs) could improve the selectivity of the O2 sensor against hydrogen peroxide (H2O2). The electrochemical results reveal that the Co porphyrin active sites facilitate the direct four-electron pathway for ORR and that the Co porphyrin-based COF, enriched with pyrene units, shows enhanced four-electron ORR kinetics and better tolerance to HPRR. The theoretical calculation suggests that introducing pyrene units essentially weakens the adsorption of H2O2, leading to suppression of the HPRR. The microsensor fabricated with the Co porphyrin-based COF as the electrocatalyst features a high selectivity for real-time monitoring of O2 in a living rat brain.

Molecular Layer Doping ZnO Films as a Novel Approach to Resistive Oxygen Sensors

In the modern world, gas sensors play a crucial role in sectors such as high-tech industries, medicine, and environmental monitoring. Among these fields, oxygen sensors are the most important. There are several types of oxygen sensors, including optical, magnetic, Schottky diode, and resistive (or chemoresistive) ones. Currently, most oxygen-resistive sensors (ORSs) described in the literature are fabricated as thick layers, typically deposited via screen printing, and they operate at high temperatures, often exceeding 700 °C. This work presents a novel approach utilizing atomic layer deposition (ALD) to create very thin layers. Combined with appropriate doping, this method aims to reduce the energy consumption of the sensors by lowering both the mass requiring heating and the operating temperature. The device fabricated using the proposed process demonstrates a response of 88.21 at a relatively low temperature of 450 °C, highlighting its potential in ORS applications based on doped ALD thin films.

Fully Passive Electrochemical Oxygen Sensor Enabled With Organic Electrochemical Transistor

AbstractWireless and battery‐free sensor operation is essential for sustainable sensor networks for environmental and health monitoring. Achieving such a fully passive design in electrochemical sensors is challenging due to the need for amplification and control electronics as realized in potentiostats. To address this issue, organic electrochemical transistors (OECTs) are introduced as amplified sensors and demonstrate an OECT‐based oxygen sensor that exploits the electrochemical reduction of oxygen, akin to the Clark electrode. To build the sensor, the transistor thin film fabrication protocol is integrated with the deposition of a gas permeable silicone membrane and a hydrogel electrolyte. To assess the sensor's power consumption, a model that links power consumption to the OECT geometry and the material properties of the semiconducting channel is established. This model identifies the optimized OECT design that is compatible with commercial near‐field communication (NFC) microcontrollers. In the optimized design, the interrogating NFC radio signal is sufficient to power the microcontroller, achieve sensor readout, and transmit the digitized sensor current, enabling oxygen monitoring in air or water without wired connections or batteries. These findings provide a first example and quantitative argumentation on exploiting OECTs in low‐power electrochemical sensor architectures.

Surface Engineering of Borophene as Next‐Generation Materials for Energy and Environmental Applications

This review provides an insightful and comprehensive exploration of the emerging 2D material borophene, both pristine and modified, emphasizing its unique attributes and potential for sustainable applications. Borophene's distinctive properties include its anisotropic crystal structures that contribute to its exceptional mechanical and electronic properties. The material exhibits superior electrical and thermal conductivity, surpassing many other 2D materials. Borophene's unique atomic spin arrangements further diversify its potential application for magnetism. Surface and interface engineering, through doping, functionalization, and synthesis of hybridized and nanocomposite borophene‐based systems, is crucial for tailoring borophene's properties to specific applications. This review aims to address this knowledge gap through a comprehensive and critical analysis of different synthetic and functionalisation methods, to enhance surface reactivity by increasing active sites through doping and surface modifications. These approaches optimize diffusion pathways improving accessibility for catalytic reactions, and tailor the electronic density to tune the optical and electronic behavior. Key applications explored include energy systems (batteries, supercapacitors, and hydrogen storage), catalysis for hydrogen and oxygen evolution reactions, sensors, and optoelectronics for advanced photonic devices. The key to all these applications relies on strategies to introduce heteroatoms for tuning electronic and catalytic properties, employ chemical modifications to enhance stability and leverage borophene's conductivity and reactivity for advanced photonics. Finally, the review addresses challenges and proposes solutions such as encapsulation, functionalization, and integration with composites to mitigate oxidation sensitivity and overcome scalability barriers, enabling sustainable, commercial‐scale applications.

Interpenetration twin morphology Fe-N-C as highly efficient oxygen reduction electrocatalysts for coulomb electrolytic oxygen sensor

Interpenetration twin morphology Fe-N-C as highly efficient oxygen reduction electrocatalysts for coulomb electrolytic oxygen sensor

OA−ICOS−Based Oxygen and Carbon Dioxide Sensors for Field Applications in Gas Reflux Chicken Coops

To facilitate the effective assessment of respiratory entropy during poultry breeding, a novel oxygen (O2) and carbon dioxide (CO2) sensor was developed based on the off−axis integrated cavity output spectroscopy technique, featuring effective absorption optical paths of 15.5 m and 8.5 m, respectively. The sensor employs integrated environmental control technology, substantially enhancing detection precision. To improve the instrument’s response speed, the miniaturization of the cavity and structural optimization were implemented, achieving a rapid response time of merely 6.22 s, addressing the stringent requirements for quick responsiveness in poultry respiration thermometry research. A signal processing model tailored for on−site applications was designed, boosting the system’s signal−to−noise ratio by 4.7 times under complex environmental noise conditions. Utilizing Allan variance analysis, the sensor’s detection limits for O2 and CO2 were ascertained to be 2.9 ppm and 7.4 ppb, respectively. A 24−h field application test conducted in Gongzhuling demonstrated that the sensor’s results align with the respiratory characteristics of poultry under normal physiological conditions, validating its extensive potential for application in respiratory analysis, environmental monitoring, and industrial sectors.

A scalable and autoclavable oxygen nanosensor platform for metabolic monitoring of Saccharomyces cerevisiae in a bioreactor and other in situ systems.

Polymer-encapsulated dye nanoparticle sensors are a valuable approach to achieving in situ analyte measurements with luminescence; however, typical emulsion-based nanosensors are poorly suited for large-scale biological samples due to limitations of synthesis scalability and stability. Branched polyethylenimine (PEI) is a versatile polymer scaffold ideal for constructing nanoparticles with various covalently conjugated moieties due to their high density of reactive primary amines, high water solubility, and biological stability. In this work, we used branched polyethylenimine as a scaffold-based approach for making a stable and scalable ratiometric oxygen sensor. Pt (II) tetracarboxyporphine was usedas an oxygen-sensing dye and coumarin 343 as a reference dye, all covalently linked to the PEI scaffold producing a product that could withstand sterilization procedures and easily be scaled. To minimize toxicity from the PEI scaffold, we conjugated it with 2000MW PEG.Theapplicability of the sensors was demonstratedin a 200mL Saccharomyces cerevisiae yeast culture, using orthogonal luminescent and electrochemical oxygen measurements to validate sensor response and measure the metabolic activity of the yeast in our culture. This approach was able to match the sensitivity of our electrochemical measurements while improving upon drawbacks of other luminescent methods of oxygen detection, demonstrating effective monitoring for at least 20h. Our scaffold-based approach is a modular and easily translatable technology that could be useful in various biotechnological applications.

A new approach to off-gas analysis for shaken bioreactors showing high CTR and RQ accuracy

BackgroundShake flasks are essential tools in biotechnological development due to their cost efficiency and ease of use. However, a significant challenge is the miniaturization of process analytical tools to maximize information output from each cultivation. This study aimed to develop a respiration activity online measurement system via off-gas analysis, named “Transfer rate Online Measurement” (TOM), for determining the oxygen transfer rate (OTR), carbon dioxide transfer rate (CTR), and the respiration quotient (RQ) in surface-aerated bioreactors, primarily targeting shake flasks.ResultsSensors for off-gas analysis were placed in a bypass system that avoids the shaking of the electronics and sensors. An electrochemical oxygen sensor and an infrared CO2 sensor were used. The bypass system was combined with the established method of recurrent dynamic measurement phases, evaluating the decrease in oxygen and the increase in CO2 during stopped aeration. The newly developed measurement system showed high accuracy, precision and reproducibility among individual flasks, especially regarding CTR measurement. The system was compared with state-of-the-art RAMOS technology (Respiration Activity Monitoring System, see explanation below) and calibrated with a non-biological model system. The accuracy of RQ measurement was +-4% for the tested range (8% filling volume, OTR and CTR: 0–56 mmol/L/h), allowing for the determination of metabolic switches and quantitative analysis of metabolites. At ambient CO2 levels, a CTR resolution of less than 0.01 mmol/L/h was possible. The system was applied to the microbial model systems S. cerevisiae, G. oxydans, and E. coli. Physiological states, such as growth vs. protein production, could be revealed, and quantitative analysis of metabolites was performed, putting focus on RQ measurements.ConclusionsThe developed TOM system showcases a novel approach to measuring OTR, CTR, and RQ in shaken bioreactors. It offers a robust and accurate solution for respiration activity analysis. Due to its flexible design and tunable accuracy, it enables measurement in various applications and different shake flasks.

Decoupling microbial iron reduction from anoxic microsite formation in oxic sediments: a microscale investigation through microfluidic models

Iron (Fe) reduction is one of the oldest microbial processes on Earth. After the atmosphere and ocean became oxygenated, this anaerobic process was relegated to niche anoxic environments. However, evidence of Fe reduction in oxic, partially saturated subsurface systems, such as soils and vadose zones, has been reported, with the common explanation being the formation of anoxic microsites that remain undetected by bulk measurements. To explore how microscale oxygen concentrations regulate microbial Fe reduction, we cultivated a facultative Fe-reducing bacterium using a microfluidic setup integrated with transparent planar oxygen sensors. Contrary to expectations, Fe reduction occurred under fully oxic conditions, without the formation of anoxic microsites. Our results suggest that microbially mediated Fe-reduction could be more widespread in oxic subsurface environments than previously assumed. Moreover, our mathematical modeling of oxygen dynamics around biomass-rich layers revealed that the onset of anoxia is mainly controlled by biomass spatial organization rather than the conventionally used water saturation index. This opens a new perspective on the proxies needed to predict anoxic microsite formation and Fe(III) reduction occurrence.

Implementation of Fuzzy Logic in Environmental Control and Disease Diagnosis of Sumatran Fish <i>Puntius tetrazona</i>

Water quality management in rearing media is an important factor to maintain fish health and survival. Optimal water quality can help fish growth and prevent disease. This research aims to develop and implement a Fuzzy Logic-based system to automate water quality management in Sumatran Puntius tetrazona fish aquariums and perform early diagnosis of several diseases that commonly attack Sumatran Puntius tetrazona fish. The use of fuzzy logic using MATLAB is very helpful in monitoring media water quality and fish diseases. This research develops a fuzzy logic-based system to control water quality and diagnose diseases of Sumatran Puntius tetrazona fish. This system uses components such as Arduino IDE, ESP32, dissolved oxygen sensor, temperature sensor, amonia sensor, and pH sensor to collect and process data related to water quality and fish disease diagnosis.

Shallow-angle intracranial cannula for repeated infusion and in vivo imaging with multiphoton microscopy.

Multiphoton microscopy serves as an essential tool for high-resolution imaging of the living mouse brain. To facilitate optical access to the brain during imaging, the cranial window surgery is commonly used. However, this procedure restricts physical access above the imaging area and hinders the direct delivery of imaging agents and drugs. To overcome this limitation, we have developed a cannula delivery system that enables the implantation of a low-profile cannula nearly parallel to the brain surface at angles as shallow as 8 degrees, while maintaining compatibility with multiphoton microscopy. To validate this approach, we perform direct infusion and imaging of various fluorescent cell markers in the brain. Additionally, we successfully demonstrate tracking of degenerating neurons over time in Alzheimer's disease mice using Fluoro-Jade C. Furthermore, we show longitudinal imaging of brain tissue partial pressure of oxygen using a phosphorescent oxygen sensor. Our developed technique should enable a wide range of new longitudinal imaging studies in the mouse brain.

Increasing the efficiency of bioreactor operation for cultivation of methane-oxidizing bacteria under conditions of decreasing carbon dioxide concentration in the cultural liquid

Objectives. The work set out to develop a bioreactor that incorporates a carbon dioxide removal unit within the apparatus gas phase, which is capable of operating without the need for supplementary compression apparatus. As part of testing the developed equipment in order to ascertain its capacity for enhanced biomass production, the principal fermentation system parameters that facilitate the optimal bioreactor productivity in conditions of carbon dioxide removal from the apparatus gas phase were identified.Methods. A series of tests were conducted on the fermentation unit with the objective of controlling the oxygen and carbon dioxide content in the gas phase of the bioreactor. This was achieved using an in-line gas analyzer fitted with electrochemical sensors. The oxygen and carbon dioxide content in the gas phase was determined by means of gas chromatography. The oxygen and natural gas flow rates were determined using a thermal electronic flow controller equipped with thermoresistive elements. The oxygen content of the cultural liquid was determined by means of an optical oxygen sensor with integrated transducer. The pH level in the bioreactor was monitored and maintained using an electrochemical pH sensor.Results. The efficacy of the newly devised jet-type bioreactor design, which permits the incorporation of a carbon dioxide removal unit into the fermentation system without requiring supplementary compression apparatus, was evaluated through experimentation. The system was tested with the carbon dioxide removal unit included in the design, resulting in a 64% increase in bioreactor productivity and a 18% reduction in oxygen consumption as a component of the gas supply.Conclusions. The operational parameters of a technological bioreactor that facilitate a stable continuous process of bacterial cultivation were identified.

Module-A Sensor Performance Tests Used In Laboratory-Type Silage Production, Data Acquisition and Control System

The primary objective of this study is to investigate the performance of sensors integrated into the laboratory-type silage production, data acquisition, and control system. The system is a PLC-controlled and multi-sensor based system designed to enable numerous studies aimed at improving silage quality. It consists of grinding, weighing, silo, data acquisition, and control units. It provides the capability to apply/change/simulate various parameters during the silage production process. The silo unit is composed of two modules, module-A (compression principle) and module-B (vacuum principle). This research focuses on measurements conducted with plexiglass silos (24,5 cm3) in the module-A unit. This silos were equipped with oxygen sensor (±0-100 %), carbon dioxide sensor (0-5000 ppm), temperature sensor (±0.53 °C, -10 – 80 °C), humidity sensor (0-100 %), pH sensor (2-12), and pressure sensor (± 1000 mbar). The research utilized second-crop silage corn material with a dry matter content (DM) of 32%. Four different compaction forces were applied during the experiments. Sensor measurements were recorded as one data per second by connecting them to the data recording unit using analog sensors. Due to the abundance of data, average values were taken. The data were displayed and monitored on the HMI operator panel programmed with GOP HMI editor software and stored in Excel format. The measurements were carried out during the silage (aerobic) and post-silage (anaerobic) periods. According to the research results, it was observed that the six tested sensors performed accurate readings. However, issues related to the oxygen and carbon dioxide sensors were encountered. Due to the difficulty in reading at points with very low oxygen content, it was decided to be supported by controlling with sensors of different types and specifications. During measurements conducted at the compression stage in module-A, the pressure values varied between 0,34-0,67 bar with increasing compaction force. The temperature ranged from 16-33 °C, humidity from 60-100 %, pH from 5,8-5,6 O2 level from 8,1-0 mmol L-1, and CO2 level from 0-40 mmol L-1. The measured value ranges in silage varied depending on the duration of silage, and accurate measurements were obtained in the desired direction. Sensor placements were updated considering measurement accuracy.

Oxygen-Dependent Photoluminescence and Electrical Conductance of Zinc Tin Oxide (ZTO): A Modified Stern-Volmer Description.

Zinc tin oxide (ZTO) is investigated as a photoluminescent sensor for oxygen (O2); chemisorbed oxygen quenches the luminescence intensity. At the same time, ZTO is also studied as a resistive sensor; being an n-type semiconductor, its electrical conductance decreases by adsorption of oxygen. Both phenomena can be exploited for quantitative O2 sensing. The respective sensor responses can be described by the same modified Stern-Volmer model that distinguishes between accessible and non-accessible luminescence centers or charge carriers, respectively. The impact of the temperature is studied in the range from room temperature up to 150 °C.

Conformational protection of molybdenum nitrogenase by Shethna protein II

The oxygen-sensitive molybdenum-dependent nitrogenase of Azotobacter vinelandii is protected from oxidative damage by a reversible ‘switch-off’ mechanism1. It forms a complex with a small ferredoxin, FeSII (ref. 2) or the ‘Shethna protein II’3, which acts as an O2 sensor and associates with the two component proteins of nitrogenase when its [2Fe:2S] cluster becomes oxidized4,5. Here we report the three-dimensional structure of the protective ternary complex of the catalytic subunit of Mo-nitrogenase, its cognate reductase and the FeSII protein, determined by single-particle cryo-electron microscopy. The dimeric FeSII protein associates with two copies of each component to assemble a 620 kDa core complex that then polymerizes into large, filamentous structures. This complex is catalytically inactive, but the enzyme components are quickly released and reactivated upon oxygen depletion. The first step in complex formation is the association of FeSII with the more O2-sensitive Fe protein component of nitrogenase during sudden oxidative stress. The action of this small ferredoxin represents a straightforward means of protection from O2 that may be crucial for the maintenance of recombinant nitrogenase in food crops.

Superhydrophobic and oleophobic luminescent composite materials for oxygen sensing in fuel-laden atmospheres

Accurate measurement and monitoring of oxygen concentration in fuel-laden atmospheres is crucial for reducing the risk of fire and explosion. Oxygen sensors based on fluorescence quenching are suitable for such...

Lithium phthalocyanine (γ-structure) as a molecular oxygen sensor.

Synthesis and characterization of lithium phthalocyanine radicals were performed, which were followed by an investigation on its ability to detect oxygen levels in biologically relevant concentrations. EPR studies confirmed the presence of at least two phases, one sensitive to oxygenation (γ-phase) and the second one insensitive to oxygenation (α-phase). Contrary to the findings reported in the literature, it was observed that the γ-phase was not stable at and above 95 °C and slowly transformed into the α-phase crystallographic structure. Above 150 °C, only a broad signal of α-phase existed. Additional characterizations were performed using electrochemical impedance spectroscopy (EIS), cyclic voltammetry, dynamic light scattering (DLS), and Raman spectroscopy on pristine crystals Li2Pc and LiPc sensors.

Fast response solid electrolyte oxygen sensors with porous thin film electrodes.

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

Luminescence Lifetime-Based Water Conductivity Sensing Using a Cationic Dextran-Supported Ru(II) Polypyridyl Complex.

Water conductivity sensing relies universally on electrical measurements, which are subject to corrosion of the electrodes and subsequent signal drift in prolonged in situ uses. Furthermore, they cannot provide contactless sensing or remote readout. To this end, a novel device for water conductivity monitoring has been developed by employing a microenvironment-sensitive ruthenium complex, [Ru(2,2'-bipyridine-4,4'-disulfonato)3]4-, embedded into a quaternary ammonium functionalized cross-linked polymer support. The degree of swelling of the latter, which leads to a change in the emission lifetime, depends on the water conductivity. The sensor displays a reversible response (2 min ≤ t90 ≤ 3 min) and has been shown to be stable for >65 h of continuous monitoring of 0.8-12.8 mS cm-1 KCl solutions. Changes to the cation do not affect the sensor response, while changes to the anion type induce small effects. Variations in the dissolved O2 or temperature require corrections of the response. The sensor can be interrogated alongside dissolved O2 and pH luminescent sensors based on the same family of indicator dyes to exploit the definite advantages of luminescence lifetime-based detection.

Metal-Enhanced Luminescence of Core-Shell Au@ Resorcinol-Formaldehyde Resin Nanospheres for Oxygen Sensing.

Luminescence-based detection has attracted widespread interests in oxygen measurement applications due to its great versatility, simplicity, sensitivity and non-invasive measurement. However, the relatively low quantum efficiency prompts a need for developing methods for luminescent enhancement. Plasmonic nanoparticles are known to efficiently enhance emission of the surrounding dyes with a precise inter-distance of nanoparticles and dyes. Here, we reported a novel plasmon-enhanced luminescence system in which the distance between luminescence dyes (PtTFPP) and metal nanoparticles (Au nanospheres, AuNSs) can be tuned by an organic spacer of Resorcinol-Formaldehyde (RF) to investigate the separation dependence on the emission enhancement in the optical oxygen sensors. A maximum enhancement of up to 6.24-fold has been achieved with a 5nm thick spacer in the PtTFPP-based oxygen sensors. These findings provide a unique platform for exploring the application of metal-enhanced luminescence (MEL) in luminescence-based measurement for oxygen concentration.