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Polymer‐metal complexes (PMCs) based on poly(2,2′‐bipyridine‐4,4′‐dicarboxamide‐co‐polydimethylsiloxanes) with cyclometalated di(2‐phenylpyridinato‐C2,N')iridium(III) fragments and cross‐linked by Zn2+ (Zn[Ir]‐BipyPDMSs) or Ir3+ (Ir[Ir]‐BipyPDMSs) represent flexible, stretchable, phosphorescent, and self‐healing molecular oxygen sensors. PMCs provide strong phosphorescence at λem = 595–605 nm. Zn[Ir]‐BipyPDMS with PDMS chain length of Mn = 5000 has the highest quantum yield of 9.3% and is a molecular oxygen sensor at different O2 concentrations (0–100 vol%) compared to Ir[Ir]‐BipyPDMSs. A Stern−Volmer constant is determined for Zn[Ir]‐BipyPDMS as KSV = 0.014%−1, which is similar to the reported oxygen‐sensitive iridium(III) complexes. All synthesized PMCs exhibit high elongation at break (up to 1100%) and self‐healing efficiency (up to 99%). [ABSTRACT FROM AUTHOR]

A series of fluorescent carbazole‐coumarins exhibiting good photoluminescence quantum yields and thermally activated delayed fluorescence (TADF) properties have been designed and synthetized using computer‐aided density functional theory calculations. The TADF characteristics of the carbazole‐coumarins were systematically explored both in solution and in the solid state, utilizing poly(methyl methacrylate) (PMMA) as a matrix. The study revealed that the introduction of carbazole units onto the coumarin benzene ring led to compounds with thermally induced reverse intersystem crossing and delayed fluorescence. The study further demonstrated the potential utility of these compounds in practical applications by incorporating them into a Cmr‐PMMA‐based sensor for molecular oxygen detection. The resulting sensor exhibited promising performance, highlighting the adaptability and efficacy of the synthesized TADF‐carbazole‐coumarin compounds for reversible molecular oxygen sensing. [ABSTRACT FROM AUTHOR]

Polymer‐network liquid crystal (PNLC) possesses both advantages of low‐molecular‐weight liquid crystal (LMWLC) and liquid crystal (LC) polymer. Herein, a two‐stage polymerization strategy for the formation of unique PNLC with oxygen‐sensing properties is reported. The reaction mixture consists of 6% diacrylate RM257, 93.5% LMWLC 4‐cyano‐4′‐pentylbiphenyl (5CB), and 0.5% photoinitiator dimethoxy‐2‐phenylacetophenone (DMPA). In the first stage, the mixture is exposed to UV light for 2 min to form a primary polymer network, which is highly uniform with a planar orientation. However, some free radicals are trapped inside the LC due to the short UV exposure time. Subsequently, the trapped free radicals are released by heating the PNLC sample into an isotropic state. Under this condition, the free radicals can move freely and react with surrounding monomers to form a secondary polymer network, which is highly disordered and scatters light strongly. Because oxygen can deactivate free radicals trapped inside the PNLC, the phenomenon to detect oxygen and monitor the diffusion of oxygen through the PNLC is exploited. The PNLC‐based oxygen sensor is potentially useful for the detection of oxygen and monitoring the exposure time to oxygen. [ABSTRACT FROM AUTHOR]

Polymer‐network liquid crystal (PNLC) possesses both advantages of low‐molecular‐weight liquid crystal (LMWLC) and liquid crystal (LC) polymer. Herein, a two‐stage polymerization strategy for the formation of unique PNLC with oxygen‐sensing properties is reported. The reaction mixture consists of 6% diacrylate RM257, 93.5% LMWLC 4‐cyano‐4′‐pentylbiphenyl (5CB), and 0.5% photoinitiator dimethoxy‐2‐phenylacetophenone (DMPA). In the first stage, the mixture is exposed to UV light for 2 min to form a primary polymer network, which is highly uniform with a planar orientation. However, some free radicals are trapped inside the LC due to the short UV exposure time. Subsequently, the trapped free radicals are released by heating the PNLC sample into an isotropic state. Under this condition, the free radicals can move freely and react with surrounding monomers to form a secondary polymer network, which is highly disordered and scatters light strongly. Because oxygen can deactivate free radicals trapped inside the PNLC, the phenomenon to detect oxygen and monitor the diffusion of oxygen through the PNLC is exploited. The PNLC‐based oxygen sensor is potentially useful for the detection of oxygen and monitoring the exposure time to oxygen.

The gas sensitivity and structural properties of TiO2 thin films deposited by plasma-enhanced atomic layer deposition (ALD) were examined in detail. The TiO2 thin films are deposited using Tetrakis(dimethylamido)titanium(IV) and oxygen plasma at 300 °C on SiO2 substrates followed by annealing at temperatures of 800 °C. Gas sensitivity under exposure to O2 within the temperature range from 30 °C to 700 °C was studied. The ALD-deposited TiO2 thin films demonstrated high responses to O2 in the dynamic range from 0.1 to 100 vol. % and low concentrations of H2, NO2. The ALD deposition allowed the enhancement of sensitivity of TiO2 thin films to gases. The greatest response of TiO2 thin films to O2 was observed at a temperature of 500 °C and was 41.5 arb. un. under exposure to 10 vol. % of O2. The responses of TiO2 thin films to 0.1 vol. % of H2 and 7 × 10–4 vol. % of NO2 at a temperature of 500 °C were 10.49 arb. un. and 10.79 arb. un., correspondingly. The resistance of the films increased due to the chemisorption of oxygen molecules on their surface that decreased the thickness of the conduction channel between the metal contacts. It was suggested that there are two types of adsorption centers on the TiO2 thin films surface: oxygen is chemisorbed in the form of O2– on the first one and O– on the second one. [ABSTRACT FROM AUTHOR]

Oxygen quantification using luminescence has attracted considerable attention in various fields, including environmental monitoring and clinical analysis. Among the reported luminophores, trivalent lanthanide complexes have displayed characteristic narrow emission bands with high brightness. This bright emission is based on photo‐sensitized energy transfer via organic triplet states. The organic triplet states in lanthanide complexes effectively react with the triplet oxygen, enabling oxygen quantification by lanthanide luminescence. Some TbIII and EuIII complexes with slow deactivation processes have also formed the excited state equilibrium, thus resulting in the emission‐lifetime based oxygen sensing property. The combination of TbIII/EuIII emission, EuIII/SmIII emission, EuIII/ligand phosphorescence, and ligand fluorescence/ligand phosphorescence provide the ratiometric oxygen‐sensing properties. Moreover, the reaction generates singlet oxygen species which exhibit numerous applications in the photo‐medical field. The ligands with large π‐conjugated aromatic systems, such as porphyrin, phthalocyanine, and polyaromatic compounds, induces highly efficient oxygen generation. The combination of effective luminescence with singlet‐oxygen generation by the lanthanide complexes render them suitable for photo‐driven theranostics. This review summarizes the research progress of lanthanide complexes with efficient oxygen‐sensing and singlet‐oxygen generation properties. [ABSTRACT FROM AUTHOR]

The measurement of oxygen consumption is an important element in the understanding of an organism's metabolic state. Oxygen is also a phosphorescence quencher, which allows the evaluation of phosphorescence emitted by oxygen sensors. Two Ru(II)-based oxygen-sensitive sensors were used to study the effect of chemical compounds [(1) = [CoCl2(dap)2]Cl, and (2) = [CoCl2(en)2]Cl (AmB = amphotericin B) against reference and clinical strains of Candida albicans. The tris-[(4,7-diphenyl-1,10-phenanthroline)ruthenium(II)] chloride ([Ru(DPP)3]Cl2) (Box) adsorbed onto the DavisilTM silica gel was embedded in the silicone rubber Lactite NuvaSil® 5091 and the coating on the bottom of 96-well plates. The water-soluble oxygen sensor (BsOx = tris-[(4,7-diphenyl-1,10-phenanthrolinedisulphonic acid disodium)ruthenium(II)] chloride 'x' hydrate = {Ru[DPP(SO3Na)2]3}Cl2 = water molecules were omitted in the BsOx formula) was synthesized and characterized by RP-UHPLC, LCMS, MALDI, elemental analysis, ATR, UV-Vis, 1H NMR, and TG/IR techniques. The microbiological studies were performed in the environment of RPMI broth and blood serum. Both Ru(II)-based sensors turned out to be useful in the study of the activity of Co(III) complexes and the commercial antifungal drug amphotericin B. In addition, a new activity of the oxygen sensor, the soluble Ru(II) complex BsOx, was demonstrated, which is a mixture with amphotericin B that caused a significant increase in its antifungal activity. Thus, it is also possible to demonstrate the synergistic effect of compounds active against the microorganisms under study. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen Optical Sensors using phenothiazinium Methylene Blue analogues. • Highly sensitive to the oxygen (O 2 < 0.01 %) in the food vacuumed packaging. • Easy airless/photochemical activation after incorporation into food packaging. • EPR and UV–vis investigation of redox processes in oxygen sensors. • Transient aminyl radicals as intermediates in the redox process. This study investigates four phenothiazinium dyes including methylene blue (MB) and three analogues containing auxochrome variation 2 – 4 as oxygen colorimetric indicators prepared by their incorporation into two types of oxygen permeable materials containing: a) polyvinyl alcohol substrate with additional TiO 2 photocatalysts (PhOxIn), and b) carboxymethylcellulose polymer matrix containing glucose and KOH (ChOxIn). In vacuum packages where volumetric concentrations of oxygen were below 0.01 %, the leuco forms of the tested phenothiazinum dyes were readily oxidised, initiating the colour turn from white to blue. The redox processes involved were explored by experimental electron paramagnetic resonance EPR and UV–vis spectroscopic methods and further supported by theoretical quantum chemistry. The EPR experiments showed that the chemical oxidation of the leuco-form of the phenothiazinium dyes 1 – 4 produced transient aminyl radical species with the single electron mainly located at the nitrogen atom of the heterocyclic core. The formation of these transient aminyl species was also perceived by UV–vis spectroscopy, their absorption maxima situated in the 552–592 nm range being also supported by TD-DFT theoretical calculations. [ABSTRACT FROM AUTHOR]

The gas sensitivity and structural properties of TiO2 thin films deposited by plasma-enhanced atomic layer deposition (ALD) were examined in detail. The TiO2 thin films are deposited using Tetrakis(dimethylamido)titanium(IV) and oxygen plasma at 300 °C on SiO2 substrates followed by annealing at temperatures of 800 °C. Gas sensitivity under exposure to O2 within the temperature range from 30 °C to 700 °C was studied. The ALD-deposited TiO2 thin films demonstrated high responses to O2 in the dynamic range from 0.1 to 100 vol. % and low concentrations of H2, NO2. The ALD deposition allowed the enhancement of sensitivity of TiO2 thin films to gases. The greatest response of TiO2 thin films to O2 was observed at a temperature of 500 °C and was 41.5 arb. un. under exposure to 10 vol. % of O2. The responses of TiO2 thin films to 0.1 vol. % of H2 and 7 × 10–4 vol. % of NO2 at a temperature of 500 °C were 10.49 arb. un. and 10.79 arb. un., correspondingly. The resistance of the films increased due to the chemisorption of oxygen molecules on their surface that decreased the thickness of the conduction channel between the metal contacts. It was suggested that there are two types of adsorption centers on the TiO2 thin films surface: oxygen is chemisorbed in the form of O2– on the first one and O– on the second one.

Abstract We utilized a seeded growth method to synthesize SiO2@Ag NPs with tunable plasmonic resonance peak to investigate the effect of spectral overlap between the SiO2@Ag plasmonic resonance spectrum and the PtTFPP‐based oxygen sensors’ absorbance spectra on luminescence enhancement and performance optimization. An organic silicate was used as the matrix. Oxygen‐sensors were produced by directly casting the mixture of NPs and dyes with silicate gels onto glass slides. Oxygen‐induced spectral response of the PtTFPP was obtained as the analytical signal. Our results show that when the plasmonic resonance spectrum of SiO2@Ag has a maximum wavelength overlap with the absorbance spectra of dyes, the Stern‐Volmer slopes were enhanced by almost an order of magnitude. At 21% O2, the Stern‐Volmer plot achieved a maximum seven‐fold increase over the oxygen sensor without the metal‐enhanced luminescence. Our results also show that 10% wt NPs is the optimal amount for the PtTFPP‐SiO2@Ag based oxygen sensors that can eliminate self‐quenching and the NRET process. These data confirm that the spectral overlap between the dyes and noble metal NPs and how to eliminate self‐quenching and the NRET process are vital to high‐sensitive oxygen sensors. We have also shown that our fabrication process of these oxygen sensors is repeatable.

Heme is a vital cofactor of proteins with roles in oxygen transport (e.g. hemoglobin), storage (e.g. myoglobin), and activation (e.g. P450) as well as electron transfer (e.g. cytochromes) and many other functions. However, its structural and functional role in oxygen sensing proteins differs markedly from that in most other enzymes, where it serves as a catalytic or functional center. This minireview discusses the mechanism of signal transduction in two heme-based oxygen sensors: the histidine kinase AfGcHK and the diguanylate cyclase YddV (EcDosC), both of which feature a heme-binding domain containing a globin fold resembling that of hemoglobin and myoglobin. [ABSTRACT FROM AUTHOR]

The present work aimed to study a family of solid ceramic electrolytes based on magnesium oxide doped zirconium oxide, usually identified as Mg-PSZ (zirconia partially stabilized with magnesia), used in the manufacture of oxygen sensors for molten metals. A set of electrolytes was prepared by mechanical (milling) and thermal (sintering) processing, varying the composition in magnesia and the cooling rate from the sintering temperature. These two parameters are essential in terms of phase composition and microstructure of Mg-PSZ, determining the behavior of these materials. The structural and microstructural characterization was done by means of X-ray diffraction (XRD). The electrical properties were analyzed by impedance spectroscopy in air. In general, the results obtained from various concentrations of dopant, different cooling rates and the same sintering step condition showed an increased conductivity for samples with predominance of high temperature stable phases (tetragonal and cubic).

The measurement of oxygen consumption is an important element in the understanding of an organism’s metabolic state. Oxygen is also a phosphorescence quencher, which allows the evaluation of phosphorescence emitted by oxygen sensors. Two Ru(II)-based oxygen-sensitive sensors were used to study the effect of chemical compounds [(1) = [CoCl2(dap)2]Cl, and (2) = [CoCl2(en)2]Cl (AmB = amphotericin B) against reference and clinical strains of Candida albicans. The tris-[(4,7-diphenyl-1,10-phenanthroline)ruthenium(II)] chloride ([Ru(DPP)3]Cl2) (Box) adsorbed onto the DavisilTM silica gel was embedded in the silicone rubber Lactite NuvaSil® 5091 and the coating on the bottom of 96-well plates. The water-soluble oxygen sensor (BsOx = tris-[(4,7-diphenyl-1,10-phenanthrolinedisulphonic acid disodium)ruthenium(II)] chloride ‘x’ hydrate = {Ru[DPP(SO3Na)2]3}Cl2 = water molecules were omitted in the BsOx formula) was synthesized and characterized by RP-UHPLC, LCMS, MALDI, elemental analysis, ATR, UV-Vis, 1H NMR, and TG/IR techniques. The microbiological studies were performed in the environment of RPMI broth and blood serum. Both Ru(II)-based sensors turned out to be useful in the study of the activity of Co(III) complexes and the commercial antifungal drug amphotericin B. In addition, a new activity of the oxygen sensor, the soluble Ru(II) complex BsOx, was demonstrated, which is a mixture with amphotericin B that caused a significant increase in its antifungal activity. Thus, it is also possible to demonstrate the synergistic effect of compounds active against the microorganisms under study.

DosT and DosS are heme-based kinases involved in sensing and signaling O 2 tension in the microenvironment of Mycobacterium tuberculosis (Mtb). Under conditions of low O 2 , they activate >50 dormancy-related genes and play a pivotal role in the induction of dormancy and associated drug resistance during tuberculosis infection. In this work, we reexamine the O 2 binding affinities of DosT and DosS to show that their equilibrium dissociation constants are 3.3±1.0 μM and 0.46±0.08 μM respectively, which are six to eight-fold stronger than what has been widely referred to in literature. Furthermore, stopped-flow kinetic studies reveal association and dissociation rate constants of 0.84 μM−1 s−1 and 2.8 s−1, respectively for DosT, and 7.2 μM−1 s−1 and 3.3 s−1, respectively for DosS. Remarkably, these tighter O 2 binding constants correlate with distinct stages of hypoxia-induced non-replicating persistence in the Wayne model of Mtb. This knowledge opens doors to deconvoluting the intricate interplay between hypoxia adaptation stages and the signal transduction capabilities of these important heme-based O 2 sensors. This work reports O 2 affinities of heme-based sensor kinases DosT and DosS, and how their K d values correlate to distinct stages of hypoxia-induced non-replicating persistence (NRP) in Mycobacterium tuberculosis. [Display omitted] • DosT and DosS are heme proteins that sense O 2 tension in Mycobacterium tuberculosis. • O 2 affinities of DosT and DosS are 3.3 ± 1.0 μM and 0.46 ± 0.08 μM, respectively. • These K d values are 6 to 8-fold stronger than those widely referred to in literature. [ABSTRACT FROM AUTHOR]

A series of [Ir(N^C)2(N^N)]+ NIR-emitting orthometalated complexes (1–7) has been prepared and structurally characterized using elemental analysis, mass-spectrometry, and NMR spectroscopy. The complexes display intense phosphorescence with vibrationally structured emission bands exhibiting the maxima in the range 713–722 nm. The DFT and TD DFT calculations showed that the photophysical characteristics of these complexes are largely determined by the properties of the metalating N^C ligands, with their major contribution into formation of the lowest S1 and T1 excited states responsible for low energy absorption and emission, respectively. Emission lifetimes of 1–7 in degassed methanol solution vary from 1.76 to 5.39 µs and show strong quenching with molecular oxygen to provide an order of magnitude lifetime reduction in aerated solution. The photophysics of two complexes (1 and 7) were studied in model physiological media containing fetal bovine serum (FBS) and Dulbecco's Modified Eagle Medium (DMEM) to give linear Stern-Volmer calibrations with substantially lower oxygen-quenching constants compared to those obtained in methanol solution. These observations were interpreted in terms of the sensors' interaction with albumin, which is an abundant component of FBS and cell media. The studied complexes displayed acceptable cytotoxicity and preferential localization, either in mitochondria (1) or in lysosomes (7) of the CHO-K1 cell line. The results of the phosphorescence lifetime imaging (PLIM) experiments demonstrated considerable variations of the sensors' lifetimes under normoxia and hypoxia conditions and indicated their applicability for semi-quantitative measurements of oxygen concentration in living cells. The complexes' emission in the NIR domain and the excitation spectrum, extending down to ca. 600 nm, also showed that they are promising for use in in vivo studies. [ABSTRACT FROM AUTHOR]

In the vicinity of metal nanostructures, phosphorescent intensity can be greatly enhanced through the localized surface plasmon resonance (LSPR). The enhancement of phosphorescence intensity in noble-metal nanoparticle (NP) systems is highly dependent on the overlap of the absorbance peak of a noble metal with that of phosphorescent dyes. When the peak of the NPs' absorption spectra has a maximum overlap with that of these dyes, the phosphorescence enhancement is the largest. Here, we use a seeded growth method to synthesize SiO2/Au NPs with tunable plasmonic resonance and compare their phosphorescence enhancement for an oxygen range of 0–21%. The measurement sensitivity of oxygen is strongly dependent on the enhancement of phosphorescence. When used with PtTFPP, when the absorbance peak of the SiO2/Au NPs has a maximum overlap with that of PtTFPP, the phosphorescence enhancement factor is as high as 7; the sensitivity of oxygen concentration is as high as 75. Moreover, we also optimize the performance by varying the number of NPs to eliminate the nonradiative energy-transfer (NRET) process and self-quenching. [ABSTRACT FROM AUTHOR]

We utilized a seeded growth method to synthesize SiO2@Ag NPs with tunable plasmonic resonance peak to investigate the effect of spectral overlap between the SiO2@Ag plasmonic resonance spectrum and the PtTFPP‐based oxygen sensors' absorbance spectra on luminescence enhancement and performance optimization. An organic silicate was used as the matrix. Oxygen‐sensors were produced by directly casting the mixture of NPs and dyes with silicate gels onto glass slides. Oxygen‐induced spectral response of the PtTFPP was obtained as the analytical signal. Our results show that when the plasmonic resonance spectrum of SiO2@Ag has a maximum wavelength overlap with the absorbance spectra of dyes, the Stern‐Volmer slopes were enhanced by almost an order of magnitude. At 21% O2, the Stern‐Volmer plot achieved a maximum seven‐fold increase over the oxygen sensor without the metal‐enhanced luminescence. Our results also show that 10% wt NPs is the optimal amount for the PtTFPP‐SiO2@Ag based oxygen sensors that can eliminate self‐quenching and the NRET process. These data confirm that the spectral overlap between the dyes and noble metal NPs and how to eliminate self‐quenching and the NRET process are vital to high‐sensitive oxygen sensors. We have also shown that our fabrication process of these oxygen sensors is repeatable. [ABSTRACT FROM AUTHOR]

Oxygen levels in tissues and organs are crucial for their normal functioning, and approaches to monitor them non-invasively have wide biological and clinical applications. In this study, we developed a method of acoustically detecting oxygenation using contrast-enhanced ultrasound (CEUS) imaging. Our approach involved the use of specially designed hemoglobin-based microbubbles (HbMBs) that reversibly bind to oxygen and alter the state-dependent acoustic response. We confirmed that the bioactivity of hemoglobin remained intact after the microbubble shell was formed, and we did not observe any significant loss of heme. We conducted passive cavitation detection (PCD) experiments to confirm whether the acoustic properties of HbMBs vary based on the level of oxygen present. The experiments involved driving the HbMBs with a 1.1 MHz focused ultrasound transducer. Through the PCD data collected, we observed significant differences in the subharmonic and harmonic responses of the HbMBs when exposed to an oxygen-rich environment versus an oxygen-depleted one. We used a programmable ultrasound system to capture high-frame rate B mode videos of HbMBs in both oxy and deoxy conditions at the same time in a two-chambered flow phantom and observed that the mean pixel intensity of deoxygenated HbMB was greater than in the oxygenated state using B-mode imaging. Finally, we demonstrated that HbMBs can circulate in vivo and are detectable by a clinical ultrasound scanner. To summarize, our results indicate that CEUS imaging with HbMB has the potential to detect changes in tissue oxygenation and could be a valuable tool for clinical purposes in monitoring regional blood oxygen levels.

The adrenal gland and its hormones regulate numerous fundamental biological processes; however, the impact of hypoxia signaling on adrenal function remains poorly understood. Here, we reveal that deficiency of HIF (hypoxia inducible factors) prolyl hydroxylase domain protein-2 (PHD2) in the adrenal medulla of mice results in HIF2α-mediated reduction in phenylethanolamine N-methyltransferase (PNMT) expression, and consequent reduction in epinephrine synthesis. Simultaneous loss of PHD2 in renal erythropoietin (EPO)-producing cells (REPCs) stimulated HIF2α-driven EPO overproduction, excessive RBC formation (erythrocytosis), and systemic hypoglycemia, which is necessary and sufficient to enhance exocytosis of epinephrine from the adrenal medulla. Based on these results, we propose that the PHD2-HIF2α axis in the adrenal medulla regulates the synthesis of epinephrine, whereas in REPCs, it indirectly induces the release of this hormone. Our findings are also highly relevant to the testing of small molecule PHD inhibitors in phase III clinical trials for patients with renal anemia. Key messages: HIF2α and not HIF1α modulates PNMT during epinephrine synthesis in chromaffin cells. The PHD2-HIF2α-EPO axis induces erythrocytosis and hypoglycemia. Reduced systemic glucose facilitates exocytosis of epinephrine from adrenal gland. [ABSTRACT FROM AUTHOR]

The regulation mechanism of the hybrid yellow catfish "Huangyou-1" was assessed under conditions of hypoxia and reoxygenation by examination of oxygen sensors and by monitoring respiratory metabolism, oxidative stress, and apoptosis. The expressions of genes related to oxygen sensors (HIF-1α, HIF-2α, VHL, HIF-1β, PHD2, and FIH-1) were upregulated in the brain and liver during hypoxia, and recovered compared with control upon reoxygenation. The expressions of genes related to glycolysis (HK1, PGK1, PGAM2, PFK, and LDH) were increased during hypoxia and then recovered compared with control upon reoxygenation. The mRNA levels of CS did not change during hypoxia in the brain and liver, but increased during reoxygenation. The mRNA levels of SDH decreased significantly only in the liver during hypoxia, but later increased compared with control upon reoxygenation in both tissues. Under hypoxic conditions, the expressions of genes related to oxidative stress (SOD1, SOD2, GSH-Px, and CAT) and the activity of antioxidant enzymes (SOD, CAT, and GSH-Px) and MDA were upregulated compared with control. The expressions of genes related to apoptosis (Apaf-1, Bax, Caspase 3, Caspase 9, and p53) were higher than those in control during hypoxic exposure, while the expressions of Bcl-2 and Cyt C were decreased. The findings of the transcriptional analyses will provide insights into the molecular mechanisms of hybrid yellow catfish "Huangyou-1" under conditions of hypoxia and reoxygenation. Overall, these findings showed that oxygen sensors of "Huangyou-1" are potentially useful biomarkers of environmental hypoxic exposure. Together with genes related to respiratory metabolism, oxidative stress and apoptosis occupy a quite high position in enhancing hypoxia tolerance. Our findings provided new insights into the molecular regulatory mechanism of hypoxia in "Huangyou-1." [ABSTRACT FROM AUTHOR]

Endogenous steroid hormones, especially glucocorticoids and mineralocorticoids, derive from the adrenal cortex, and drastic or sustained changes in their circulatory levels affect multiple organ systems. Although hypoxia signaling in steroidogenesis has been suggested, knowledge on the true impact of the HIFs (Hypoxia-Inducible Factors) in the adrenocortical cells of vertebrates is scant. By creating a unique set of transgenic mouse lines, we reveal a prominent role for HIF1α in the synthesis of virtually all steroids in vivo. Specifically, mice deficient in HIF1α in adrenocortical cells displayed enhanced levels of enzymes responsible for steroidogenesis and a cognate increase in circulatory steroid levels. These changes resulted in cytokine alterations and changes in the profile of circulatory mature hematopoietic cells. Conversely, HIF1α overexpression resulted in the opposite phenotype of insufficient steroid production due to impaired transcription of necessary enzymes. Based on these results, we propose HIF1α to be a vital regulator of steroidogenesis as its modulation in adrenocortical cells dramatically impacts hormone synthesis with systemic consequences. In addition, these mice can have potential clinical significances as they may serve as essential tools to understand the pathophysiology of hormone modulations in a number of diseases associated with metabolic syndrome, auto-immunity or even cancer. [ABSTRACT FROM AUTHOR]

A series of [Ir(N^C)2(N^N)]+ NIR-emitting orthometalated complexes (1–7) has been prepared and structurally characterized using elemental analysis, mass-spectrometry, and NMR spectroscopy. The complexes display intense phosphorescence with vibrationally structured emission bands exhibiting the maxima in the range 713–722 nm. The DFT and TD DFT calculations showed that the photophysical characteristics of these complexes are largely determined by the properties of the metalating N^C ligands, with their major contribution into formation of the lowest S1 and T1 excited states responsible for low energy absorption and emission, respectively. Emission lifetimes of 1–7 in degassed methanol solution vary from 1.76 to 5.39 µs and show strong quenching with molecular oxygen to provide an order of magnitude lifetime reduction in aerated solution. The photophysics of two complexes (1 and 7) were studied in model physiological media containing fetal bovine serum (FBS) and Dulbecco’s Modified Eagle Medium (DMEM) to give linear Stern-Volmer calibrations with substantially lower oxygen-quenching constants compared to those obtained in methanol solution. These observations were interpreted in terms of the sensors’ interaction with albumin, which is an abundant component of FBS and cell media. The studied complexes displayed acceptable cytotoxicity and preferential localization, either in mitochondria (1) or in lysosomes (7) of the CHO-K1 cell line. The results of the phosphorescence lifetime imaging (PLIM) experiments demonstrated considerable variations of the sensors’ lifetimes under normoxia and hypoxia conditions and indicated their applicability for semi-quantitative measurements of oxygen concentration in living cells. The complexes’ emission in the NIR domain and the excitation spectrum, extending down to ca. 600 nm, also showed that they are promising for use in in vivo studies.

Oxygen (O2) quantification is essential for assessing cell metabolism, and its consumption in cell culture is an important indicator of cell viability. Recent advances in microfluidics have made O2 sensing a crucial feature for organ-on-chip (OOC) devices for various biomedical applications. OOC O2 sensors can be categorized, based on their transducer type, into two main groups, optical and electrochemical. In this review, we provide an overview of on-chip O2 sensors integrated with the OOC devices and evaluate their advantages and disadvantages. Recent innovations in optical O2 sensors integrated with OOCs are discussed in four main categories: (i) basic luminescence-based sensors; (ii) microparticle-based sensors; (iii) nano-enabled sensors; and (iv) commercial probes and portable devices. Furthermore, we discuss recent advancements in electrochemical sensors in five main categories: (i) novel configurations in Clark-type sensors; (ii) novel materials (e.g., polymers, O2 scavenging and passivation materials); (iii) nano-enabled electrochemical sensors; (iv) novel designs and fabrication techniques; and (v) commercial and portable electrochemical readouts. Together, this review provides a comprehensive overview of the current advances in the design, fabrication and application of optical and electrochemical O2 sensors.

Gas sensors based on transition metal dichalcogenides (TMDCs) have attracted much attention from a new perspective involving light‐assisted or gate‐voltage operation. However, their combined roles as regards the gas sensing performance and mechanism are not yet understood due to the lack of controlled studies. This study systematically investigates the oxygen sensor performance and mechanism of few‐layer‐thick rhenium disulfide (ReS2) field‐effect transistors (FETs) under light illumination and gate biasing. As a result, a combination of light illumination and positive gate voltage enhances the device response over 100% at a 1% oxygen concentration; that is, the approach achieves a practical sensitivity of 0.01% ppm−1, which outperforms most of the reports available in the literature. Furthermore, the fabricated devices exhibit long‐term stability and stable operation even under humid conditions, indicating the ability of the sensor device to operate in a real‐time application. These results contribute to the development of versatile tunable oxygen sensors based on TMDC FETs. [ABSTRACT FROM AUTHOR]

We exploit a high‐performing resistive‐type trace oxygen sensor based on 2D high‐mobility semiconducting Bi2O2Se nanoplates. Scanning tunneling microscopy combined with first‐principle calculations confirms an amorphous Se atomic layer formed on the surface of 2D Bi2O2Se exposed to oxygen, which contributes to larger specific surface area and abundant active adsorption sites. Such 2D Bi2O2Se oxygen sensors have remarkable oxygen‐adsorption induced variations of carrier density/mobility, and exhibit an ultrahigh sensitivity featuring minimum detection limit of 0.25 ppm, long‐term stability, high durativity, and wide‐range response to concentration up to 400 ppm at room temperature. 2D Bi2O2Se arrayed sensors integrated in parallel form are found to possess an oxygen detection minimum of sub‐0.25 ppm ascribed to an enhanced signal‐to‐noise ratio. These advanced sensor characteristics involving ease integration show 2D Bi2O2Se is an ideal candidate for trace oxygen detection. [ABSTRACT FROM AUTHOR]

Understanding factors influencing seawater chemistry variability in coral reef environments is a major challenge to improve predictions of their evolution in the context of ocean acidification. In this study, autonomous sensors for current speed and direction, photosynthetically active radiation (PAR), temperature, salinity, dissolved oxygen (DO) and pH T were deployed three times between 2021 and 2022 offshore and on three reef flat sites of the main fringing reef of La Reunion Island. Discrete sampling of seawater for DO, pH T and total alkalinity (TA) at different times of the day complemented the monitoring. Diurnal variation of those variables on the reef flat was mainly driven by benthic community metabolism but hydrodynamics and reef geomorphology played also a key role. DO and pH T variations were decoupled in time, especially at night when we observed DO rebounds while pH T values were stationary. The reef flat was also largely TA depleted compared to offshore waters. We hypothesize that the strong offshore-alongshore current redirected TA depleted water exiting from reef channels into the reef flat. This seawater re-entrainment could also explain specific variations of DO and pH T values. This result highlights the important role of reef geomorphology in modulating changes in seawater chemistry. Neglecting this phenomenon could lead to substantial errors in the estimation of carbonate budgets when using the Eulerian approach. • Seawater chemistry on La Saline reef is modulated by hydrodynamics and geomorphology. • Dissolved oxygen and pH T variations are decoupled in time on La Saline fringing reef. • Water exiting the reef by the channels is re-entrained on the reef flat. • Water re-entrained on the reef flat appears TA depleted. • The Eulerian approach can lead to errors in the estimation of CaCO 3 budgets. [ABSTRACT FROM AUTHOR]

Keywords: central metabolism; hypoxia; metabolic architecture; oxygen sensors; seed development and germination; sugar allocation inside seeds EN central metabolism hypoxia metabolic architecture oxygen sensors seed development and germination sugar allocation inside seeds 476 478 3 09/23/21 20211015 NES 211015 What inspired your interest in plant science? There was the strong wish to study biology with a focus on plant biology/physiology, and, at that time, this was best possible at the Humboldt University in Berlin. For example, I remember work with a prototype of oxygen sensor foil, enabling the instant visualization of plant respiration (across tissues and seed sections). [Extracted from the article]

A comparative study is presented on the photoluminescence (PL) response toward molecular oxygen (O2) in tin dioxide (SnO2), zinc oxide (ZnO) and titanium dioxide (TiO2) nanoparticles. The findings show that both PL enhancement and PL quenching can be observed on different materials, arguably depending on the spatial localization of the defects responsible for the PL emission in each different oxide. No significant results are evidenced for SnO2 nanoparticles. ZnO with red/orange emission shown an O2-induced PL enhancement, suggesting that the radiative emission involves holes trapped in surface vacancy oxygen centers. While the ZnO results are scientifically interesting, its performances are inferior to the ones shown by TiO2, which exhibits the most interesting response in terms of sensitivity and versatility of the response. In particular, O2 concentrations in the range of few percent and in the range of a few tenths of a part per million are both detectable through the same mixed-phase TiO2 sample, whose rutile phase gives a reversible and fast response to larger (0.4–2%) O2 concentration while its anatase phase is usable for detection in the 25–75 ppm range. The data for rutile TiO2 suggest that its surfaces host deeply trapped electrons at large densities, allowing good sensitivities and, more notably, a relatively unsaturated response at large concentrations. Future work is expected to improve the understanding and modeling of the photophysical framework that lies behind the observations.

Featured Application: Nanosensors for extracellular oxygen-sensing. Three four-arm amphiphilic block copolymers with different chain lengths, consisting of a hydrophilic chain of polyethylene glycol (PEG) and hydrophobic segment of polycaprolactam (PCL), were synthesized and used to encapsulate the high-efficient and hydrophobic oxygen probe of platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP) to form polymer micelles. This approach enabled the use of PtTFPP in aqueous solution for biosensing. Experimental results demonstrated that the particle sizes of these nano-oxygen sensors between 40.0 and 203.8 nm depend on the structures of block copolymers. PtTFPP in these micelles showed an effective quantum yield under nitrogen environment, ranging from 0.06 to 0.159. The new sensors are suitable for analyzing dissolved oxygen concentrations in the range of 0.04–39.3 mg/L by using the linear Stern–Volmer equation at room temperature. In addition, it has been shown that these sensors are capable of in situ monitoring the dissolved oxygens in the culture medium of E. coli and Romas cells during the respiration process, and distinguishing the drug activity of antibiotic ampicillin from that of antimycin A. This study showed that the use of these nanostructured multi-arm block copolymer micelles can achieve efficient biological applications without specific structural modification of the hydrophobic PtTFPP probe, which is expected to have broad prospects. [ABSTRACT FROM AUTHOR]

Oxygen‐sensitive and near‐infrared (NIR) luminescent YbIII coordination polymers incorporating ligands based on pyrene derivatives were synthesized: YbIII–TBAPy and YbIII–TIAPy (TBAPy: 1,3,6,8‐tetrakis(p‐benzoate)pyrene; TIAPy: 1,3,6,8‐tetrakis(3,5‐isophthalic acid)pyrene). The coordination structures of these materials have been characterized by means of electrospray ionization mass spectrometry, X‐ray diffraction analysis, and thermogravimetric analysis. Moreover, the porous structure of YbIII–TIAPy has been evaluated by measuring its N2 adsorption isotherm. The NIR luminescence properties of YbIII–TBAPy and YbIII–TIAPy have been examined by acquiring emission spectra and determining emission lifetimes under air or argon and in vacuo. YbIII–TIAPy exhibited high thermal stability (with a decomposition temperature of 400 °C), intense luminescence (with an emission quantum yield under argon of 6.6 %), and effective oxygen‐sensing characteristics. These results suggest that NIR luminescent YbIII coordination polymers prepared using pyrene derivatives could have applications in novel thermo‐stable oxygen sensors. [ABSTRACT FROM AUTHOR]

Abstract In this work, the functionalization degree of siloxane crosslinkers by allyldiphenylphosphine oxide (adppo) and its effect on the performance of a lanthanide-based optical oxygen sensor were evaluated. Linear poly(dimethyl-co-hydromethylsiloxane) (PMS) and cyclic tetramethylcyclotetrasiloxane (D4i) crosslinkers were functionalized with different concentrations of adppo to chemically bond the [Tb(dcba) 3 ]·1/2H 2 O (dcba = dichlorobenzoate) complex. Mechanically stable luminescent silicone membranes were obtained after the curing of the poly(dimethylsiloxane)-vinyl terminated siloxane backbone with the pre-functionalized crosslinkers. Sensing materials exhibit green emission upon 350 nm excitation, and their luminescent properties are dependent of functionalization degree of the crosslinkers. The luminescent sensor materials show fully reversible response and non-linear Stern-Volmer plots, which are fitted by two quenching parameter model, with highest KSV of 0.08930%−1 when using functionalized D4i as crosslinker and complex concentration of 0.75%. [ABSTRACT FROM AUTHOR]

Abstract A library of 1,2- cyclometalated Pt(II) complexes based on various bidentate N ,C-chelate chromophores have been studied for their uses as luminescent oxygen sensing probes (OSPs). The bidentate chelate ligands have been found to have a distinct impact on the performance of the Pt(II) compounds as OSPs. For some of the complexes, attachment of a dimesityl boron group (BMes 2) to the chelate ligands enhances their oxygen sensitivity. For phenyl-1,2,3-triazole (Phtrz) based Pt(II) complexes, the attachment of a diphenyl amino moiety to the N ,C-chelate ligand substantially enhances phosphorescence quenching and the performance of the OSP. A high k SV app value (0.0667 Torr−1) for the OSP based on the diphenyl amino functionalized Pt(II) complex was achieved, which is the highest value reported to date for OSPs based on bidentate Pt(II) complexes. Graphical abstract Image 1 Highlights • A library of N ,C-chelate Pt(II) compounds were examined for use as oxygen sensors. • Some of the Pt(II) compounds have been found to be highly efficient oxygen sensors in polym matrices. • Substituents were found to have a key impact on stability and sensitivity of the oxygen sensors. [ABSTRACT FROM AUTHOR]

In this paper recurrent neural networks are used for modelling of the exhaust gas aftertreatment system of a spark-ignition engine including a three-way catalytic converter and oxygen sensors. Different network architectures are compared based on their achieved mean squared error. We find that physically inspired architectures surpass naive architectures built without knowledge of the physical system. The best resulting model is evaluated by giving the quantiles of the absolute error. [ABSTRACT FROM AUTHOR]

Hypoxia frequently occurs in aquatic ecosystem, which is influenced by salinity, water temperature, weather, and surface water runoff. In order to shed further light on the evolutionary and adaptive mechanisms in fish under hypoxic condition, the impact of acute hypoxia (1.63 ± 0.2 mg/L) and reoxygenation (7.0 ± 0.3 mg/L) on oxygen sensors, energy metabolism, and hematological indices was evaluated in Takifugu fasciatus. Data from transcriptional level analysis show that the expressions of genes related to oxygen sensors (HIF-1α, PHD2, and VHL) were upregulated in the brain and liver under hypoxia and recovered under reoxygenation. The upregulation of GLUT2, VEGF-A, and EPO in conjugation with VEGF-A protein and hematological indices conferred the rapid adjustments of cellular glucose uptake and blood oxygen-carrying capacities in pufferfish. Higher levels of glycolysis-related mRNAs (HK, PGK1, and PGAM2), HK activity, and proteins (PGK1 and PGAM2) were detected in the brain and liver under hypoxic condition compared with control. Interestingly, the expression of MDH1 at the mRNA, enzyme activity, and protein levels was significantly increased in the brain at 0 or 2 h and in the liver at 8 h under hypoxic condition. In addition, although the enzyme activity and mRNA expression of LDH in the brain were not significantly changed, a persistent upregulation was observed in the liver during hypoxia exposure. This study demonstrated that pufferfish could counterpoise the energetic demands and hematological functional properties evoked by oxygen sensors after hypoxia. Our findings provided new insights into the molecular regulatory mechanism of hypoxia in pufferfish. [ABSTRACT FROM AUTHOR]

Optical fiber-based sensors are uniquely suited for in-situ sensing applications that involve high operational temperature and harsh chemical conditions, such as solid oxide fuel cell (SOFC) monitoring, chemical manufacturing, and power generation. Single crystal optical fiber, such as α-alumina (sapphire), provides a substrate that exhibits improved stability over off-the-shelf silica fiber at temperatures above 800 °C. In this work, single crystal sapphire fiber is paired with a high-temperature stable perovskite oxide sensing layer, SrTi 0.65 Fe 0.35 FeO 3-δ (STF35), to demonstrate all-optical oxygen sensing from 0.01 to 0.19 atm at extreme temperatures (800–1000 °C). The defect chemistry associated with the optical oxygen sensing response is also considered within the context of the current literature and modeled under relevant sensor conditions. Stability is evaluated under dry and humid conditions, and low cross-sensitivity with CO 2 is demonstrated, indicating viability for operation on the cathode stream within an operational SOFC or within a post-combustion environment. • Sensor developed using a perovskite oxide sensing layer on single crystal fiber. • Sensor exhibits fast, stable optical response to oxygen up to 1000 °C. • Sensing mechanism evaluated in the context of oxide defect chemistry. • Cross-sensitivities and stability tested for post-combustion environment. [ABSTRACT FROM AUTHOR]

• The yttria-stabilized zirconia (YSZ) solid electrolyte oxygen sensor with LSCF (lanthanum strontium cobalt ferrite)/air reference electrode was investigated. • The performance of two LSCF/air reference electrode sensors was tested on a LBE dynamic loop. • This study demonstrates that the LSCF/air sensor can be used to monitor oxygen concentration in non-isothermal LBE systems. Oxygen sensors are the major part of the active oxygen control system (OCS) to be used in the liquid lead–bismuth eutectic (LBE) system. In this paper, the electromotive force (EMF) measured by yttria stabilized zirconia (YSZ) solid electrolyte sensor with LSCF (lanthanum strontium cobalt ferrite)/air reference electrode in static oxygen saturated LBE is used to obtain relationship between EMF and temperature. The EMF output by oxygen sensors is deterministic and predictable. At the same time, the performance of oxygen sensors in flow loop of liquid LBE were also studied. EMF output curves of oxygen sensors corresponding to the operation of consuming dissolved oxygen are given. It is proved that the LSCF/air sensor can be used to monitor oxygen concentration in non-isothermal LBE systems. [ABSTRACT FROM AUTHOR]

Low oxygen tension or hypoxia is a determining factor in the course of many different processes in animals, including when tissue expansion and cellular metabolism result in high oxygen demands that exceed its supply. This is mainly happening when cells actively proliferate and the proliferating mass becomes distant from the blood vessels, such as in growing tumors. Metabolic alterations in response to hypoxia can be triggered in a direct manner, such as the switch from oxidative phosphorylation to glycolysis or inhibition of fatty acid desaturation. However, as the modulated action of hypoxia-inducible factors or the oxygen sensors (prolyl hydroxylase domain-containing enzymes) can also lead to changes in enzyme expression, these metabolic changes can also be indirect. With this review, we want to summarize our current knowledge of the hypoxia-induced changes in metabolism during cancer development, how they are affected in the tumor cells and in the cells of the microenvironment, most prominently in immune cells.

Mono-dispersed polystyrene-based microspheres with diameters about 1 μm encapsulating rhodamine moieties as oxygen insensitive internal reference probes and platinum octaethylporphyrin units as oxygen sensitive probes were synthesized as new ratiometric oxygen sensors (Rhod-PtOEP-PS). The dual luminophors of rhodamines and platinum porphyrin moieties exhibited emissions maxima at 585 nm and 644 nm, respectively. The microspheres showed good oxygen sensing properties in different oxygen partial pressures (pO 2 ) and dissolved oxygen (DO) concentrations. It was found the oxygen probes and reference probes in microspheres showed higher photo-stability than their corresponding free fluorophores in solution. The microspheres also showed good sensitivity for air-pressure and cellular oxygen in cell culture medium. These microspheres were used to detect DOs in a few kinds of liquids including some daily drinks and it was found the measured errors were within positive/negative 11% as compared with the measured results using traditional oxygen electrodes. [ABSTRACT FROM AUTHOR]

Perovskite nanocrystals (PNCs) have emerged as advanced materials for various applications. Herein, we developed oxygen insensitive PNCs in polymer matrices and applied them as internal reference to achieve ratiometric sensing for oxygen. Significant emission color changes from orange under nitrogen to green under oxygen were observed. Further micro-patterned sensors were prepared by micro/nano-imprint technology. Results showed that all these micro-structures increased sensors’ sensitivity, however, affected sensors response time significantly. The film with pinholes slowed down the response times; the films with pillars shorted the response time. Therefore, for the first time we prepared new PNCs-based ratiometric gaseous oxygen sensing films and further prepared micro-structured sensors. This study may broaden the applications of perovskite materials and also oxygen sensors. [ABSTRACT FROM AUTHOR]

Analysis of the transcriptomic changes produced in response to hypoxia in root tissues from two rootstock Prunus genotypes differing in their sensitivity to waterlogging: resistant Myrobalan ‘P.2175′ ( P. cerasifera Erhr.), and sensitive ‘Felinem’ hybrid [ P. amygdalus Batsch × P. persica (L.) Batsch] revealed alterations in both metabolism and regulatory processes. Early hypoxia response in both genotypes is characterized by a molecular program aimed to adapt the cell metabolism to the new conditions. Upon hypoxia conditions, tolerant Myrobalan represses first secondary metabolism gene expression as a strategy to prevent the waste of resources/energy, and by the up-regulation of protein degradation genes probably leading to structural adaptations to long-term response to hypoxia. In response to the same conditions, sensitive ‘Felinem’ up-regulates a core of signal transduction and transcription factor genes. A combination of PLS-DA and qRT-PCR approaches revealed a set of transcription factors and signalling molecules as differentially regulated in the sensitive and tolerant genotypes including the peach orthologs for oxygen sensors. Apart from providing insights into the molecular processes underlying the differential response to waterlogging of two Prunus rootstocks, our approach reveals a set of candidate genes to be used expression biomarkers for biotech or breeding approaches to waterlogging tolerance. [ABSTRACT FROM AUTHOR]

Selective oxidative functionalization of molecules is a highly relevant and often demanding reaction in organic chemistry. The use of biocatalysts allows the stereo- and regioselective introduction of oxygen molecules in organic compounds at milder conditions and avoids the use of complex group-protection schemes and toxic compounds usually applied in conventional organic chemistry. The identification of enzymes with the adequate properties for the target reaction and/or substrate requires better and faster screening strategies. In this manuscript, a microchannel with integrated oxygen sensors was applied to the screening of wild-type and site-directed mutated variants of naphthalene dioxygenase (NDO) from Pseudomonas sp. NICB 9816-4. The oxygen sensors were used to measure the oxygen consumption rate of several variants during the conversion of styrene to 1-phenylethanediol. The oxygen consumption rate allowed the distinguishing of endogenous respiration of the cell host from the oxygen consumed in the reaction. Furthermore, it was possible to identify the higher activity and different reaction rate of two variants, relative to the wild-type NDO. The meander microchannel with integrated oxygen sensors can therefore be used as a simple and fast screening platform for the selection of dioxygenase mutants, in terms of their ability to convert styrene, and potentially in terms of substrate specificity. [ABSTRACT FROM AUTHOR]

Front Cover: Luminescent Lanthanide Complexes for Effective Oxygen-Sensing and Singlet Oxygen Generation (ChemPlusChem 6/2023) Keywords: lanthanide; luminescence; oxygen sensors; singlet oxygen; triplet states EN lanthanide luminescence oxygen sensors singlet oxygen triplet states 1 1 1 06/28/23 20230601 NES 230601 B The front cover picture shows b triplet-oxygen sensing and singlet-oxygen generation using lanthanide complexes. Lanthanide, luminescence, oxygen sensors, singlet oxygen, triplet states. [Extracted from the article]