Transcutaneous pO2imaging during tourniquet-induced forearm ischemia using planar optical oxygen sensors

Calculation of Tissue Oxygenation via an Inverse Boundary Problem for Transcutaneous Oxygenation Wearable Applications

In this article, we present a toolset to fully leverage a previously developed transcutaneous oxygenation monitor (TCOM) wearable technology to accurately measure skin oxygenation values. We describe numerical models and experimental characterization techniques that allow for the extraction of precise tissue oxygenation measurements. The numerical model is based on an inverse boundary problem of the parabolic equation with Dirichlet boundary conditions. To validate this model and characterize the diffusion of oxygen through the oxygen sensing materials, we designed a series of control/calibration experiments modeled after the device's clinical application using oxygenation values in the physiological range expected for healthy tissue. Our results demonstrate that it is possible to obtain accurate tissue pO2 measurements without the need for long equilibration times with a small wearable device.

Upper arm versus forearm transcutaneous oximetry during upper limb abduction in patients with suspected thoracic outlet syndrome

Context: Thoracic outlet syndrome (TOS) is common among athletes and should be considered as being of arterial origin only if patients have “clinical symptoms due to documented symptomatic ischemia.” We previously reported that upper limb ischemia can be documented with DROPm (minimal value of limb changes minus chest changes) from transcutaneous oximetry (TcpO2) in TOS.

Purpose: We aimed to test the hypothesised that forearm (F-) DROPm would better detect symptoms associated with arterial compression during abduction than upper arm (U-) DROPm, and that the thresholds would differ.

Methods: We studied 175 patients (retrospective analysis of a cross-sectional acquired database) with simultaneous F-TcpO2 and U-TcpO2 recordings on both upper limbs, and considered tests to be positive (CS+) when upper limb symptoms were associated with ipsilateral arterial compression on either ultrasound or angiography. We determined the threshold and diagnostic performance with a receiver operating characteristic (ROC) curve analysis and calculation of the area under the ROC curve (AUROC) for absolute resting TcpO2 and DROPm values to detect CS+. For all tests, a two-tailed p < 0.05 was considered indicative of statistical significance.

Results: In the 350 upper-limbs, while resting U-TcpO2 and resting F-TcpO2 were not predictive of CS + results, the AUROCs were 0.68 ± 0.03 vs. 0.69 ± 0.03 (both p < 0.01), with the thresholds being −7.5 vs. −14.5 mmHg for the detection of CS + results for U-DROPm vs. F-DROPm respectively.

Conclusion: In patients with suspected TOS, TcpO2 can be used for detecting upper limb arterial compression and/or symptoms during arm abduction, provided that different thresholds are used for U-DROPm and F-DROPm.

Clinical Trial Registration:ClinicalTrials.gov, identifier NCT04376177.

Advances in Flexible Organic Photodetectors: Materials and Applications

Future electronics will need to be mechanically flexible and stretchable in order to enable the development of lightweight and conformal applications. In contrast, photodetectors, an integral component of electronic devices, remain rigid, which prevents their integration into everyday life applications. In recent years, significant efforts have been made to overcome the limitations of conventional rigid photodetectors, particularly their low mechanical deformability. One of the most promising routes toward facilitating the fabrication of flexible photodetectors is to replace conventional optoelectronic materials with nanomaterials or organic materials that are intrinsically flexible. Compared with other functional materials, organic polymers and molecules have attracted more attention for photodetection applications due to their excellent photodetection performance, cost-effective solution-fabrication capability, flexible design, and adaptable manufacturing processes. This article comprehensively discusses recent advances in flexible organic photodetectors in terms of optoelectronic, mechanical properties, and hybridization with other material classes. Furthermore, flexible organic photodetector applications in health-monitoring sensors, X-ray detection, and imager devices have been surveyed.

Evaluation of the Influence of Short Tourniquet Ischemia on Tissue Oxygen Saturation and Skin Temperature Using Two Portable Imaging Modalities

BACKGROUND

The exact influence of tourniquet ischemia on a treated extremity remains unclear.

METHODS

Twenty patients received an operation on one hand under tourniquet ischemia. Twenty healthy volunteers received 10 min of tourniquet ischemia on one of their arms. Measurements of tissue oxygen saturation using near-infrared reflectance-based imaging and skin temperature of the dorsum of the hand were performed at five different timepoints (t0 was performed just before the application of the tourniquet ischemia, t1 directly after the application of the tourniquet ischemia, t2 before the release of the ischemia, t3 directly after the release of the ischemia, and t4 on the following day).

RESULTS

In both groups, tissue oxygen saturation dropped after the application of the tourniquet ischemia compared to t0 and increased after the release of the tourniquet ischemia. In the patient group, tissue oxygen saturation at t4 was higher compared to t0; in contrast, the level of tissue oxygen saturation in the participant group dropped slightly at t4 compared to t0. The measured skin temperature in the patient group showed an increase during the observation period, while it continuously decreased in the group of healthy participants.

CONCLUSIONS

Short-term ischemia did not appear to permanently restrict perfusion in this study design. The non-invasive imaging modalities used were easy to handle and allowed repetitive measurement.

Quantitative Luminescence Photography of a Swellable Hydrogel Dressing with a Traffic-Light Response to Oxygen

Sensor-integrated wound dressings are emerging tools applicable to a wide variety of medical applications from emergency triage to at-home monitoring. Uncomfortable, unnecessary wound dressing changes may be avoided by providing quantitative insight into tissue characteristics related to wound healing such as tissue oxygenation, pH, and exudate/transudate volume. Here, a simple cost-effective methodology for quantifying oxygen and pH in a swellable hydrogel dressing using a single photograph is presented. The red and green luminescence of a novel dendritic polyamine Pt-porphyrin and fluorescein conjugate quantitatively responds to oxygen and pH, respectively, and enables robust sensing. The porphyrin conjugate, when combined with a four-arm star polyethylene glycol (PEG) amine polymer, rapidly crosslinks at room temperature with an N-hydroxysuccinimide (NHS)-PEG crosslinker to form a color-changing hydrogel dressing with tunable swelling capabilities applicable to a variety of wound environments. An inexpensive digital single-lens reflex (DSLR) camera modified with bandpass filters captures the hydrogel luminescence using simple macroscopic photography, and conversion to HSB colorspace allows for intensity-independent image analysis of the hydrogels' dual modality response. The hydrogel formulation exhibits a robust and validated visible red-orange-green "traffic light" spectrum in response to oxygen changes, regardless of swelling state, pH, or autofluorescence from skin, thereby enabling the clinician friendly naked-eye feedback.

Wearable device for remote monitoring of transcutaneous tissue oxygenation

Wearable devices have found widespread applications in recent years as both medical devices as well as consumer electronics for sports and health tracking. A metric of health that is often overlooked in currently available technology is the direct measurement of molecular oxygen in living tissue, a key component in cellular energy production. Here, we report on the development of a wireless wearable prototype for transcutaneous oxygenation monitoring based on quantifying the oxygen-dependent phosphorescence of a metalloporphyrin embedded within a highly breathable oxygen sensing film. The device is completely self-contained, weighs under 30 grams, performs on-board signal analysis, and can communicate with computers or smartphones. The wearable measures tissue oxygenation at the skin surface by detecting the lifetime and intensity of phosphorescence, which undergoes quenching in the presence of oxygen. As well as being insensitive to motion artifacts, it offers robust and reliable measurements even in variable atmospheric conditions related to temperature and humidity. Preliminary in vivo testing in a porcine ischemia model shows that the wearable is highly sensitive to changes in tissue oxygenation in the physiological range upon inducing a decrease in limb perfusion.

A paintable phosphorescent bandage for postoperative tissue oxygen assessment in DIEP flap reconstruction

Flaps are common in plastic surgery to reconstruct large tissue defects in cases such as trauma or cancer. However, most tissue oximeters used for monitoring ischemia in postoperative flaps are bulky, wired devices, which hinder direct flap observation. Here, we present the results of a clinical trial using a previously untried paintable transparent phosphorescent bandage to assess the tissue's partial pressure of oxygen (pO2). Statistical analysis revealed a strong relationship (P < 0.0001) between the rates of change of tissue oxygenation measured by the bandage and blood oxygen saturation (%stO2) readings from a standard-of-care ViOptix near-infrared spectroscopy oximeter. In addition, the oxygen-sensing bandage showed no adverse effects, proved easy handling, and yielded bright images across all skin tones with a digital single-lens reflex (DSLR) camera. This demonstrates the feasibility of using phosphorescent materials to monitor flaps postoperatively and lays the groundwork for future exploration in other tissue oxygen sensing applications.

Mapping O2 concentration in ex-vivo tissue samples on a fast PLIM macro-imager

O2 PLIM microscopy was employed in various studies, however current platforms have limitations in sensitivity, image acquisition speed, accuracy and general usability. We describe a new PLIM imager based on the Timepix3 camera (Tpx3cam) and its application for imaging of O2 concentration in various tissue samples stained with a nanoparticle based probe, NanO2-IR. Upon passive staining of mouse brain, lung or intestinal tissue surface with minute quantities of NanO2-IR or by microinjecting the probe into the lumen of small or large intestine fragments, robust phosphorescence intensity and lifetime signals were produced, which allow mapping of O2 in the tissue within 20 s. Inhibition of tissue respiration or limitation of O2 diffusion to tissue produced the anticipated increases or decreases in O2 levels, respectively. The difference in O2 concentration between the colonic lumen and air-exposed serosal surface was around 140 µM. Furthermore, subcutaneous injection of 5 µg of the probe in intact organs (a paw or tail of sacrificed mice) enabled efficient O2 imaging at tissue depths of up to 0.5 mm. Overall, the PLIM imager holds promise for metabolic imaging studies with various ex vivo models of animal tissue, and also for use in live animals.

Transcutaneous oxygen measurement using ratiometric fluorescence imaging as a valid method for monitoring free flap transplants

BACKGROUND

Reconstruction of soft tissue defects with free flaps is a common procedure in plastic and reconstructive surgery. Most postoperative complications occur within the first 48-72 hours after surgery. After postoperative complications, short perfusion restoration times may improve flap survival rates by up to 30-50%. Ratiometric fluorescence imaging is an additional or alternative method of postoperative flap monitoring.

OBJECTIVE

To test the efficacy and utility of transepidermal oxygen flux imaging to evaluate postoperative skin oxygenation of free and local flaps in the first 48 hours after surgery.

METHODS

The study included 32 patients (aged between 18 and 80 years; mean age 52.9) with a tissue defect covered with a free flap transplant at the Department of Plastic and Reconstructive Surgery of the University Medical Center Regensburg. Postoperative oxygen flux was measured with the 'VisiSens system' placed on the vascular pedicle as well as on the peripheral and central part of the flap.

RESULTS

Values of oxygen flux were higher in case of flap congestion (0.069±0.012) or flap necrosis (0.155±0.083) than in cases without any complications (0.061±0.006). Flux values of different areas of the same flap showed only minimal differences (central part: 0.065±0.008, peripheral part: 0.070±0.009, vascular pedicle: 0.056±0.004); the level of significance was p = 0.904.

CONCLUSION

Imaging transepidermal oxygen flux by ratiometric luminescence seems to be a reliable alternative, indirect method of postoperative flap monitoring with regard to microcirculatory function and flap viability.

Continuous monitoring of interstitial tissue oxygen using subcutaneous oxygen microsensors: In vivo characterization in healthy volunteers

Measurements of regional tissue oxygen serve as a proxy to monitor local perfusion and have the potential to guide therapeutic decisions in multiple clinical disciplines. Transcutaneous oximetry (tcpO2) is a commercially available noninvasive technique that uses an electrode to warm underlying skin tissue and measure the resulting oxygen tension at the skin surface. A novel approach is to directly measure interstitial tissue oxygen using subcutaneous oxygen microsensors composed of a biocompatible hydrogel carrier platform with embedded oxygen sensing molecules. After initial injection of the hydrogel into subcutaneous tissue, noninvasive optical measurements of phosphorescence-based emissions at the skin surface are used to sense oxygen in the subcutaneous interstitial space. The object of the present study was to characterize the in vivo performance of subcutaneous microsensors and compare with transcutaneous oximetry (tcpO2). Vascular occlusion tests were performed on the arms of 7 healthy volunteers, with repeated tests occurring 1 to 10 weeks after sensor injection, yielding 95 total tests for analysis. Comparative analysis characterized the response of both devices to decreases in tissue oxygen during occlusion and to increases in tissue oxygen following release of the occlusion. Results indicated: (I) time traces returned by microsensors and tcpO2 were highly correlated, with the median (interquartile range) correlation coefficient of r = 0.93 (0.10); (II) both microsensors and tcpO2 sensed a statistically significant decrease in normalized oxygen during occlusion (p < 0.001 for each device); (III) microsensors detected faster rates change (p < 0.001) and detected overshoot during recovery more frequently (38% vs. 4% of tests); (IV) inter-measurement analysis showed no correlation of baseline values between microsensors and tcpO2 (r = 0.03), but comparison of integrated oxygen dynamics showed similar variation in the normalized response to occlusion between devices (p = 0.06), (V) intra-measurement analysis revealed that microsensors detect greater physiological fluctuations than tcpO2 (p < 0.001) and may provide enhanced sensitivity to processes such as vasomotion. Additionally, the functional response of microsensors was not significantly different across time groupings (per month) post-injection (p = 0.61). Although the compared devices have differences in the mechanisms used to sense oxygen, these findings demonstrate that subcutaneous oxygen microsensors measure changes in interstitial tissue oxygen in human subjects in vivo.

Microvascular Response to the Roos Test Has Excellent Feasibility and Good Reliability in Patients With Suspected Thoracic Outlet Syndrome

Background: Exercise oximetry allows operator-independent recordings of microvascular blood flow impairments during exercise and can be used during upper arm provocative maneuvers.

Objective: To study the test-retest reliability of upper-limb oximetry during the Roos test in patients with suspected thoracic outlet syndrome (TOS).

Materials and Methods: Forty-two patients (28 men, 14 women; mean age: 40.8 years) were examined via transcutaneous oxygen pressure (TcpO2) recordings during two consecutive Roos tests in the standing position. The minimal decrease from rest of oxygen pressure (DROPmin) value was recorded after each maneuver was performed on both arms. The area under the receiver operating characteristic (ROC) curve defined the DROPmin diagnostic performance in the presence of symptoms during the tests. The Mann–Whitney U-test was used to compare the DROPmin in the symptomatic vs. asymptomatic arms. The test-retest reliability was analyzed with Bland-Altman representations. The results are presented as means ± standard deviations (SD) or medians [25–75 percentiles].

Results: The symptoms by history were different from the symptoms expressed during the Roos maneuvers in one-third of the patients. The DROPmin measurements were −19 [−36; −7] mmHg and −8 [−16; −5] mmHg in the symptomatic (n = 108) and asymptomatic (n = 60) arms, respectively. When TOS observed on ultrasound imaging was the endpoint, the area under the ROC curve (AUC) was 0.725 ± 0.058, with an optimal cutoff point of −15 mmHg. This value provided 67% sensitivity and 78% specificity for the presence TOS via ultrasound. When symptoms occurring during the test represented the endpoint, the AUC was 0.698 ± 0.04, with a cutoff point of −10 mmHg. This provided 62% sensitivity and 66% specificity for the presence of pain in the ipsilateral arm during the test. The test-retest reliability of DROPmin proved to be good but not perfect, partly because of unreliability of the provocation maneuvers.

Conclusion: To the best of our knowledge, this study is the first to investigate microvascular responses during the Roos maneuver in patients with suspected TOS. The presence of symptoms was significantly associated with ischemia. TcpO2 facilitated the recording of both macrovascular and microvascular responses to the Roos test. The Roos maneuver should probably be performed at least twice in patients with suspected TOS.

Wearable, Luminescent Oxygen Sensor for Transcutaneous Oxygen Monitoring

We present a new concept for a wearable oxygen (O₂) sensor for transcutaneous O₂ pressure (tcpO₂) monitoring by combining the technologies of luminescent gas sensing and wearable devices. O₂ monitoring has been exhaustively studied given its central role in diagnosing various diseases. The ability to quantify the physiological distribution and real-time dynamics of O₂ from the subcellular to the macroscopic level is required to fully understand mechanisms associated with both normal physiological and pathological conditions. Despite its profound biological and clinical importance, few effective methods exist for noninvasively quantifying O₂ in a physiological setting. The wearable sensor developed here consists of three components: a luminescent sensing film attached onto skin by a carbon tape, an organic light-emitting diode (OLED) as a light source, and an organic photodiode (OPD) as a light detector. All the components are solution-processable and integrated on a plane in a bandage-like configuration. To verify the performance, tcpO₂ variations by pressure-induced occlusion were measured in the lower arm and a thumb by the wearable sensor, and the results were comparable to those measured by a commercial instrument. In addition to its flexibility, other features of this sensor render it a potential low-cost solution for the simultaneous monitoring of tcpO₂ in any part of a body.

Transcutaneous oxygen measurement in humans using a paramagnetic skin adhesive film

PURPOSE

Transcutaneous oxygen tension (TcpO₂ ) provides information about blood perfusion in the tissue immediately below the skin. These data are valuable in assessing wound healing problems, diagnosing peripheral vascular/arterial insufficiency, and predicting disease progression or the response to therapy. Currently, TcpO₂ is primarily measured using electrochemical skin sensors, which consume oxygen and are prone to calibration errors. The goal of the present study was to develop a reliable method for TcpO₂ measurement in human subjects.

METHODS

We have developed a novel TcpO₂ oximetry method based on electron paramagnetic resonance (EPR) principles with an oxygen-sensing skin adhesive film, named the superficial perfusion oxygen tension (SPOT) chip. The SPOT chip is a 3-mm diameter, 60-μm thick circular film composed of a stable paramagnetic oxygen sensor. The chip is covered with an oxygen-barrier material on one side and secured on the skin by a medical adhesive transfer tape to ensure that only the oxygen that diffuses through the skin surface is measured. The method quantifies TcpO₂ through the linewidth of the EPR spectrum.

RESULTS

Repeated measurements using a cohort of 10 healthy human subjects showed that the TcpO₂ measurements were robust, reliable, and reproducible. The TcpO₂ values ranged from 7.8 ± 0.8 to 22.0 ± 1.0 mmHg in the volar forearm skin (N = 29) and 8.1 ± 0.3 to 23.4 ± 1.3 mmHg in the foot (N = 86).

CONCLUSIONS

The results demonstrated that the SPOT chip can measure TcpO₂ reliably and repeatedly under ambient conditions. The SPOT chip method could potentially be used to monitor TcpO₂ in the clinic.

Imaging of oxygen and hypoxia in cell and tissue samples

Molecular oxygen (O2) is a key player in cell mitochondrial function, redox balance and oxidative stress, normal tissue function and many common disease states. Various chemical, physical and biological methods have been proposed for measurement, real-time monitoring and imaging of O2 concentration, state of decreased O2 (hypoxia) and related parameters in cells and tissue. Here, we review the established and emerging optical microscopy techniques allowing to visualize O2 levels in cells and tissue samples, mostly under in vitro and ex vivo, but also under in vivo settings. Particular examples include fluorescent hypoxia stains, fluorescent protein reporter systems, phosphorescent probes and nanosensors of different types. These techniques allow high-resolution mapping of O2 gradients in live or post-mortem tissue, in 2D or 3D, qualitatively or quantitatively. They enable control and monitoring of oxygenation conditions and their correlation with other biomarkers of cell and tissue function. Comparison of these techniques and corresponding imaging setups, their analytical capabilities and typical applications are given.

Transcutaneous oximetry: variability in normal values for the upper and lower limb

INTRODUCTION

Published normal transcutaneous oxygen partial pressures (P_tcO₂) for the chest and lower limb have defined tissue hypoxia as a value of < 40 mmHg (< 30 mmHg in some patients, < 50 mmHg in others).

AIM

To determine 'normal' P_tcO₂ for the upper and lower limb in healthy, non-smoking adults using the Radiometer® TCM400 with tc Sensor E5250.

METHOD

Thirty-two volunteers had transcutaneous oxygen measurements (TCOM) performed on the chest, upper and lower limbs breathing air, with leg then arm elevated and whilst breathing 100% oxygen.

RESULTS

Room-air P_tcO₂ (mmHg, mean (95% confidence interval)) were: chest: 53.6 (48.7-58.5); upper arm: 60.0 (56.1-64.0); forearm: 52.3 (44.8-55.8); dorsum of hand: 50.2 (46.1-54.3); thenar eminence: 70.8 (67.7-73.8); hypothenar eminence: 77.9 (75.1-80.7); lateral leg: 50.2 (46.2-54.2); lateral malleolus: 50.5 (46.6-54.3); medial malleolus: 48.9 (45.6-52.1); dorsum, between first and second toe: 53.1 (49.2-57.0); dorsum, proximal to fifth toe: 58.5 (55.0 - -62.0); plantar, 1st MTP: 73.7 (70.3-77.1). Nineteen subjects had at least one room-air P_tcO₂ below 40 mmHg (nine upper limb, 13 lower limb, four chest). Approximately 10% lower limb P_tcO₂ were < 100 mmHg on normobaric oxygen. Only one subject at one site had an upper limb P_tcO₂ < 100 mmHg breathing oxygen.

CONCLUSION

The broad dispersion in P_tcO₂ in our healthy cohort reflects the inherent biologic variability in dermal perfusion and oxygen delivery, making it difficult to define narrow, rigid 'normal' values. Thus, we cannot recommend a single P_tcO₂ value as 'normal' for the upper or lower limb. A thorough patient assessment is essential to establish appropriateness for hyperbaric oxygen therapy, with TCOM used as an aid to guide this decision and not as an absolute.

Transepidermal oxygen flux during arterial occlusion using ratiometric luminescence imaging

BACKGROUND

A physiological oxygen transport through a circulatory and microcirculatory system is essential for execution of cellular functions. Several pathological conditions e.g. infections, ischemia, cancer, diabetes, hypertension or chronic wounds show a change of oxygen distribution and oxygen tension in cellular microenvironment. Additionally complex operative procedures in order to reconstruct tissue defects require a reliable monitoring of microcirculation.

OBJECTIVE

Target of this study was to evaluate skin oxygenation during an ischemia-reperfusion experiment using transepidermal oxygen flux imaging.

METHODS

Twelve patients at the Department of Plastic and Reconstructive surgery of the University hospital of Regensburg underwent to elective hand operations. During the operation a tourniquet is standardly set on the upper arm to create ischemia in order to facilitate the operative procedure. Measurements were performed at the different time intervals: in rest, under ischemia and after reperfusion.

RESULTS

The transepidermal oxygen flux increased during the ischemic condition compared to normal condition and decreased to a lower value during reperfusion (rest: 0.043±0.007, ischemia: 0.063±0.014, reperfusion: 0.030±0.028).

CONCULSION

Transepidermal oxygen flux imaging by ratiometric luminescence imaging seems to be a reliable tool to assess skin oxygenation. However dynamic changes seem to be more informative than absolute thresholds. Further investigations are necessary to prove these promising results.

Transepidermal oxygen flux measurement - First clinical application for postoperative wound monitoring

BACKGROUND

Measurement of skin oxygen is of great interest in diverse fields of medicine. Different pathologies, e.g. infection, ischemia cancer or chronic wounds show a characteristic oxygen distribution and skin oxygen tension. Additionally diverse operative procedures require a reliable postoperative monitoring in order to ensure success of the therapy.

OBJECTIVE

Aim of this study was to assess transepidermal oxygen flux for postoperative wound monitoring after operative treatment of fractures close to the hip.

METHODS

22 patients underwent transepidermal oxygen flux measurement at the first postoperative day. Transepidermal oxygen flux measurement was performed using ratiometric luminescence imaging. Examination was conducted in close proximity to the operation wound. The corresponding area at the contralateral side served as reference.

RESULTS

Oxygen flux in the operation area was higher (0.084±0.021) than the contralateral side (0.071±0.029).

CONCLUSIONS

Transepidermal oxygen flux imaging by ratiometric luminescence imaging seems to be a reliable tool to assess postoperative wound healing. However further investigations in greater populations and under pathologic conditions have to be performed to prove these first results.

Oxygen Sensing Difluoroboron β-Diketonate Polylactide Materials with Tunable Dynamic Ranges for Wound Imaging

Difluoroboron β-diketonate poly(lactic acid) materials exhibit both fluorescence (F) and oxygen sensitive room-temperature phosphorescence (RTP). Introduction of halide heavy atoms (Br and I) is an effective strategy to control the oxygen sensitivity in these materials. A series of naphthyl-phenyl (nbm) dye derivatives with hydrogen, bromide and iodide substituents were prepared for comparison. As nanoparticles, the hydrogen derivative was hypersensitive to oxygen (0-0.3%), while the bromide analogue was suited for hypoxia detection (0-3% O₂). The iodo derivative, BF₂nbm(I)PLA, showed excellent F to RTP peak separation and an 0-100% oxygen sensitivity range unprecedented for metal-free RTP emitting materials. Due to the dual emission and unconventionally long RTP lifetimes of these O₂ sensing materials, a portable, cost-effective camera was used to quantify oxygen levels via lifetime and red/green/blue (RGB) ratiometry. The hypersensitive H dye was well matched to lifetime detection, simultaneous lifetime and ratiometric imaging was possible for the bromide analogue, whereas the iodide material, with intense RTP emission and a shorter lifetime, was suited for RGB ratiometry. To demonstrate the prospects of this camera/material design combination for bioimaging, iodide boron dye-PLA nanoparticles were applied to a murine wound model to detect oxygen levels. Surprisingly, wound oxygen imaging was achieved without covering (i.e. without isolating from ambient conditions, air). Additionally, would healing was monitored via wound size reduction and associated oxygen recovery, from hypoxic to normoxic. These single-component materials provide a simple tunable platform for biological oxygen sensing that can be deployed to spatially resolve oxygen in a variety of environments.

Hypoxia and hypoxia-inducible factors in myeloid cell-driven host defense and tissue homeostasis

The impact of tissue oxygenation and hypoxia on immune cells has been recognized as a major determinant of host defense and tissue homeostasis. In this review, we will summarize the available data on tissue oxygenation in inflamed and infected tissue and the effect of low tissue oxygenation on myeloid cell function. Furthermore, we will highlight effects of the master regulators of the cellular hypoxic response, hypoxia-inducible transcription factors (HIF), in myeloid cells in antimicrobial defense and tissue homeostasis.

Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

We review the current state of optical methods for sensing oxygen. These have become powerful alternatives to electrochemical detection and in the process of replacing the Clark electrode in many fields. The article (with 694 references) is divided into main sections on direct spectroscopic sensing of oxygen, on absorptiometric and luminescent probes, on polymeric matrices and supports, on additives and related materials, on spectroscopic schemes for read-out and imaging, and on sensing formats (such as waveguide sensing, sensor arrays, multiple sensors and nanosensors). We finally discuss future trends and applications and summarize the properties of the most often used indicator probes and polymers. The ESI† (with 385 references) gives a selection of specific applications of such sensors in medicine, biology, marine and geosciences, intracellular sensing, aerodynamics, industry and biotechnology, among others.

Culture media from hypoxia conditioned endothelial cells protect human intestinal cells from hypoxia/reoxygenation injury

Remote ischemic preconditioning (RIPC) is a phenomenon, whereby short episodes of non-lethal ischemia to an organ or tissue exert protection against ischemia/reperfusion injury in a distant organ. However, there is still an apparent lack of knowledge concerning the RIPC-mediated mechanisms within the target organ and the released factors. Here we established a human cell culture model to investigate cellular and molecular effects of RIPC and to identify factors responsible for RIPC-mediated intestinal protection. Human umbilical vein cells (HUVEC) were exposed to repeated episodes of hypoxia (3 × 15 min) and conditioned culture media (CM) were collected after 24h. Human intestinal cells (CaCo-2) were cultured with or without CM and subjected to 90 min of hypoxia/reoxygenation injury. Reverse transcription-polymerase chain reaction, Western blotting, gelatin zymography, hydrogen peroxide measurements and lactate dehydrogenase (LDH) assays were performed. In HUVEC cultures hypoxic conditioning did not influence the profile of secreted proteins but led to an increased gelatinase activity (P<0.05) in CM. In CaCo-2 cultures 90 min of hypoxia/reoxygenation resulted in morphological signs of cell damage, increased LDH levels (P<0.001) and elevated levels of hydrogen peroxide (P<0.01). Incubation of CaCo-2 cells with CM reduced the hypoxia-induced signs of cell damage and LDH release (P<0.01) and abrogated the hypoxia-induced increase of hydrogen peroxide. These events were associated with an enhanced phosphorylation status of the prosurvival kinase Erk1/2 (P<0.05) but not Akt and STAT-5. Taken together, CM of hypoxia conditioned endothelial cells protect human intestinal cells from hypoxia/reoxygenation injury. The established culture model may help to unravel RIPC-mediated cellular events and to identify molecules released by RIPC.

FRET excited ratiometric oxygen sensing in living tissue

Dynamic analysis of oxygen (O₂) has been limited by the lack of a real-time, quantitative, and biocompatible sensor. To address these demands, we designed a ratiometric optode matrix consisting of the phosphorescence quenching dye platinum (II) octaethylporphine ketone (PtOEPK) and nanocystal quantum dots (NQDs), which when embedded within an inert polymer matrix allows long-term pre-designed excitation through fluorescence resonance energy transfer (FRET). Depositing this matrix on various glass substrates allowed the development of a series of optical sensors able to measure interstitial oxygen concentration [O₂] with several hundred millisecond temporal resolution in varying biological microdomains of active brain tissue.

Indicators for optical oxygen sensors

Continuous monitoring of oxygen concentration is of great importance in many different areas of research which range from medical applications to food packaging. In the last three decades, significant progress has been made in the field of optical sensing technology and this review will highlight the one inherent to the development of oxygen indicators. The first section outlines the bioanalytical fields in which optical oxygen sensors have been applied. The second section gives the reader a comprehensive summary of the existing oxygen indicators with a critical highlight on their photophysical and sensing properties. Altogether, this review is meant to give the potential user a guide to select the most suitable oxygen indicator for the particular application of interest.

Anaerobic vs aerobic pathways of carbonyl and oxidant stress in human lens and skin during aging and in diabetes: A comparative analysis

The effects of anaerobic (lens) vs aerobic (skin) environment on carbonyl and oxidant stress are compared using de novo and existing data on advanced glycation and oxidation products in human crystallins and collagen. Almost all modifications increase with age. Methylglyoxal hydroimidazolones, carboxymethyllysine, and carboxyethyllysine are severalfold higher in lens than in skin and markedly increase upon incubation of lens crystallins with 5mM ascorbic acid. In contrast, fructose-lysine, glucosepane crosslinks, glyoxal hydroimidazolones, metal-catalyzed oxidation (allysine), and H(2)O(2)-dependent modifications (2-aminoapidic acid and methionine sulfoxide) are markedly elevated in skin, but relatively suppressed in the aging lens. In both tissues ornithine is the dominant modification, implicating arginine residues as the principal target of the Maillard reaction in vivo. Diabetes (here mostly type 2 studied) increases significantly fructose-lysine and glucosepane in both tissues (P<0.001) but has surprisingly little effect on the absolute level of most other advanced glycation end products. However, diabetes strengthens the Spearman correlation coefficients for age-related accumulation of hydrogen peroxide-mediated modifications in the lens. Overall, the data suggest that oxoaldehyde stress involving methylglyoxal from either glucose or ascorbate is predominant in the aging noncataractous lens, whereas aging skin collagen undergoes combined attack by nonoxidative glucose-mediated modifications, as well as those from metal-catalyzed oxidation and H(2)O(2).