Changes In H2O2 Concentration Research Articles

Smartphone-Integrated Automated Sensor Employing Electrochemically Engineered 3D Bimetallic Nanoflowers for Hydrogen Peroxide Quantification in Milk.

Hydrogen peroxide (H2O2), one of the reactive oxygen species in living beings, serves as a regulator of various cellular processes. However, excessive peroxide concentrations are linked to oxidative stress and promptly disrupt cellular components, leading to several pathological conditions in the body. Moreover, it is extremely reactive and has a limited lifetime; thus, H2O2 sensing remains a prominent focus of research. Enzymatic sensing probes were widely employed to detect H2O2 in the recent past; however, they are susceptible to intrinsic chemical and thermal instabilities, which decrease the reliability and durability of the surface. This research was designed to come up with a feasible solution to this problem. Herein, a novel nonenzymatic peroxidase-mimic three-dimensional (3D) bimetallic nanoflower has been synergistically engineered for quick sensing of H2O2. The sensor platform showed minimal resistance or enhanced charge transfer properties as well as remarkable analytical capability, having a broad linear range between 0.01 and 1 nM and a detection limit of 1.46 ± 0.07 pM. The probe responded to changes in H2O2 concentration in just 2.10 ± 0.02 s, making it a quick sensing platform for H2O2 tracking. This peroxidase-mimic nanozyme probe showed minimal sensitivity to interferants often seen in real-world sample matrices and possessed good recoveries ranging from 92.88 to 99.09% in milk samples. Further, a facile and user-friendly smartphone application (APP) named "HPeroxide-Check" was developed and integrated into the sensor to check the milk adulteration by detecting H2O2. It processes the current output obtained from the sensing interface and provides real-time peroxide concentrations in milk. The entire procedure of fabricating the probe is a single, highly robust step that takes only 10 min and is coupled with a smartphone APP, highlighting the sensor's quick manufacturing and deployment for automated H2O2 monitoring in industrial and point-of-care settings.

Assessment of hydrogen peroxide as a bioindicator of stress in seaweed aquaculture

The rapid expansion in commercial seaweed farming has highlighted the need for more effective monitoring methods, and health diagnostics. The production of the reactive oxygen species (ROS) hydrogen peroxide (H2O2) is a trait that is tied to all major macroalgal groups and holds significance both for its involvement in the oxidative stress response and in the production of climatically relevant gases such as halocarbons. Observations of increased production of H2O2 by plants as a stress response, along with its comparative stability and ease of quantification in seawater in comparison to other ROS, suggest that H2O2 could be used as an indicator of health. In this study we characterized aqueous H2O2 dynamics across a diel cycle, in response to small shifts in light and temperature, as well as when exposed to acute stress. Our results reveal that exposure to acute stressors leads to rapid and sustained concentrations of H2O2 that are orders of magnitude higher than changes in H2O2 concentrations observed throughout the day. These findings provide tantalizing evidence that monitoring H2O2 could be used as a health indicator in seaweed aquaculture and serve as an early warning sign of stress.

Generation of Hydrogen Peroxide and Phenolic Content in Plant-Material-Based Beverages and Spices

Phenolics are the main components of plant extracts contributing to their antioxidant activity. However, they autoxidize, generating hydrogen peroxide. This study aimed to examine the correlation between the phenolic content, total antioxidant capacity (TAC), and the amount of H2O2 generated in extracts of 18 various plant materials. A significant correlation was found between the phenolic content and TAC measured by ABTS● decolorization, CUPRAC, FRAP, and DPPH● decolorization methods (correlation coefficients r of 0.94, 0.93, 0.90, and 0.78, respectively). However, the correlation between the phenolic content and H2O2 amount generated upon brewing (r = 0.25) and after 1 h incubation (r = −0.37) was low or negative. The correlation between the phenolic content and the change of H2O2 concentration during 1 h incubation of the extracts was negative (r = −0.61). Examination of three phenolics (pyrogallol, gallic acid, and quercetin) showed that all compounds generate but also scavenge H2O2. Therefore, the H2O2 concentrations in phenolic-containing extracts represent net results of the rates of generation and scavenging of H2O2, which may differ depending on the composition of phenolics in the extracts, do not always increase with the increase in time and concentration of phenolics, and cannot serve as an index of the phenolic content.

Discharge modes and liquid interactions for plasma-bubble discharges

Plasma bubbles are regarded as a promising means of interacting plasma discharges and liquids due to their high efficiency in the generation of reactive species. The discharge mode and characteristics are significant factors that should be considered. In this study, the plasmas are initially generated in the gas phase and then driven by the gas flow to diffuse into the solution through the two holes at the lower part of the quartz tube to form plasma bubbles. The discharge modes, characteristics, and plasma–liquid interactions in two different configurations, i.e., bare electrode and dielectric-coated electrode, are investigated. It is found that the discharge mode induced for the two structures is different, with a hybrid-mode operating in the bare electrode design and a filamentary mode operating in the dielectric design. When the applied voltage is increased, a filamentary-to-spark transition occurs in the bare structure, while the discharge remains relatively stable in the dielectric design. Direct and intense contact between the discharge and the solution in the bare structure greatly promotes the physio-chemical reactions and results in obvious changes in H2O2 concentration, solution pH, conductivity, and temperature. This study provides insights into hybrid gas–liquid discharges and reactor design for plasma bubble generation.

Effect of relative humidity on hydrogen peroxide production in water droplets.

Mist is generated by ultrasonic cavitation of water (Fisher Biograde, pH5.5-6.5) at room temperature (20-25°C) in open air with nearly constant temperature (22-25°C) but varying relative humidity (RH; 24-52%) over the course of many months. Water droplets in the mist are initially about 7 μm in diameter at about 50% RH. They are collected, and the concentration of hydrogen peroxide (H2O2) is measured using commercial peroxide test strips and by bromothymol blue oxidation. The quantification method is based on the Fenton chemistry of dye degradation to determine the oxidation capacity of water samples that have been treated by ultrasonication. It is found that the hydrogen peroxide concentration varies nearly linearly with RH over the range studied, reaching a low of 2 parts per million (ppm) at 24% RH and a high of 6ppm at 52% RH. Some possible public health implications concerning the transmission of respiratory viral infections are suggested for this threefold change in H2O2 concentration with RH.

Experiment design and bacterial abundance control extracellular H<sub>2</sub>O<sub>2</sub> concentrations during four series of mesocosm experiments

Abstract. The extracellular concentration of H2O2 in surface aquatic environments is controlled by a balance between photochemical production and the microbial synthesis of catalase and peroxidase enzymes to remove H2O2 from solution. In any kind of incubation experiment, the formation rates and equilibrium concentrations of reactive oxygen species (ROSs) such as H2O2 may be sensitive to both the experiment design, particularly to the regulation of incident light, and the abundance of different microbial groups, as both cellular H2O2 production and catalase–peroxidase enzyme production rates differ between species. Whilst there are extensive measurements of photochemical H2O2 formation rates and the distribution of H2O2 in the marine environment, it is poorly constrained how different microbial groups affect extracellular H2O2 concentrations, how comparable extracellular H2O2 concentrations within large-scale incubation experiments are to those observed in the surface-mixed layer, and to what extent a mismatch with environmentally relevant concentrations of ROS in incubations could influence biological processes differently to what would be observed in nature. Here we show that both experiment design and bacterial abundance consistently exert control on extracellular H2O2 concentrations across a range of incubation experiments in diverse marine environments. During four large-scale (>1000 L) mesocosm experiments (in Gran Canaria, the Mediterranean, Patagonia and Svalbard) most experimental factors appeared to exert only minor, or no, direct effect on H2O2 concentrations. For example, in three of four experiments where pH was manipulated to 0.4–0.5 below ambient pH, no significant change was evident in extracellular H2O2 concentrations relative to controls. An influence was sometimes inferred from zooplankton density, but not consistently between different incubation experiments, and no change in H2O2 was evident in controlled experiments using different densities of the copepod Calanus finmarchicus grazing on the diatom Skeletonema costatum (<1 % change in [H2O2] comparing copepod densities from 1 to 10 L−1). Instead, the changes in H2O2 concentration contrasting high- and low-zooplankton incubations appeared to arise from the resulting changes in bacterial activity. The correlation between bacterial abundance and extracellular H2O2 was stronger in some incubations than others (R2 range 0.09 to 0.55), yet high bacterial densities were consistently associated with low H2O2. Nonetheless, the main control on H2O2 concentrations during incubation experiments relative to those in ambient, unenclosed waters was the regulation of incident light. In an open (lidless) mesocosm experiment in Gran Canaria, H2O2 was persistently elevated (2–6-fold) above ambient concentrations; whereas using closed high-density polyethylene mesocosms in Crete, Svalbard and Patagonia H2O2 within incubations was always reduced (median 10 %–90 %) relative to ambient waters.

In situ Fabrication of Biological Chitosan and Gelatin-Based Hydrogels Loading Biphasic Calcium Phosphate Nanoparticles for Bone Tissue Regeneration

Adjustably biodegradable materials have gained much attention in biomedical applications. Among of them, various hydrogel-based scaffolds have applied for regenerating soft and hard tissues. In this study, according to differently biological properties of gelatin or chitosan as well as biphasic calcium phosphate nanoparticles (BCPNPs), several injectable nanocomposite hydrogels (INgel) were enzymatically fabricated from a phenolic chitosan derivative (PCD), phenolic gelatin derivative (PGD) and BCPNPs. According the change of H2O2 concentration with follow-up the time, the in situ formation of INgel was varied from 35 to 80 s. The degradation rate of the nanocomposite materials significantly related to in presence of collagenase that expended from 3 days to over one month depending on amount of the formulated PCD. The BCPNPs-encapsulated PCD-PGD INgel enhanced mineralization in the simulated biofluid. Fluorescent cytotoxicity assay indicated that the INgel was fabricated from a higher amount of the PGD resulting in a significant proliferation of bone marrow mesenchymal stem cells. These preliminary results exhibited a great potential of the INgel for bone regeneration.

Highly sensitive chemiluminescence sensing system for organophosphates using mimic LDH supported ZIF-8 nanocomposite

Developing a new detection system for reliable recognition of threatening organophosphate poisons (OPs) is a challenging subject for analysts to control their undesirable effects. Here, a sensitive analytical assay for OPs was reported based on the high mimetic behavior of layered double hydroxides supported ZIF-8 nanocomposite (LDH@ZIF-8). The well-known inhibiting effect of OP analytes on the enzymatic activity of acetylcholinesterase (AChE) was exerted to gain a suitable selectivity. Following that, efficient chemiluminescence (CL) system assisted by LDH@ZIF-8 was employed to monitor the variation in the amount of produced H2O2. It is found that the synthesized LDH@ZIF-8 possess a high effective peroxidase-like activity and can remarkably enhance the emission of the ultra-weak rhodamine B (RhoB)-H2O2 CL reaction. More studied was done using fluorometric to ratify the mimetic properties of LDH@ZIF-8 nanocomposite. The high catalytic effect of developed nanocomposite assured the high efficacy of the CL system to detect the small changes in H2O2 concentration, resulting in a high sensitivity in the detection of OPs. The low-priced and simple synthesized LDH@ZIF-8 catalyst, as well as a simple and easy-to-use CL system can be beneficial in the development of an on-site and portable detection tools. A wide linear range of 0.5–300 nM was achieved for the determination of diazinon (as a model OP), and the detection limit was as low as 0.22 nM. The method showed high reproducibility and was reassured by its application for the analysis of environmental samples.

Extracellular hydrogen peroxide measurements using a flow injection system in combination with microdialysis probes – Potential and challenges

There is a strong need for techniques that can quantify the important reactive oxygen species hydrogen peroxide (H2O2) in complex media and in vivo. We combined chemiluminescence-based H2O2 measurements on a commercially available flow injection analysis (FIA) system with sampling of the analyte using microdialysis probes (MDPs), typically used for measurements in tissue. This allows minimally invasive, quantitative measurements of extracellular H2O2 concentration and dynamics utilizing the chemiluminescent reaction of H2O2 with acridinium ester. By coupling MDPs to the FIA system, measurements are no longer limited to filtered, liquid samples with low viscosity, as sampling via a MDP is based on a dynamic exchange through a permeable membrane with a specific cut-off. This allows continuous monitoring of dynamic changes in H2O2 concentrations, alleviates potential pH effects on the measurements, and allows for flexible application in different media and systems. We give a detailed description of the novel experimental setup and its measuring characteristics along with examples of application in different media and organisms to highlight its broad applicability, but also to discuss current limitations and challenges. The combined FIA-MDP approach for H2O2 quantification was used in different biological systems ranging from marine biology, using the model organism Exaiptasia pallida (light stress induced H2O2 release up to ~ 2.7 µM), over biomedical applications quantifying enzyme dynamics (glucose oxidase in a glucose solution producing up to ~ 60 µM H2O2 and the subsequent addition of catalase to monitor the H2O2 degradation process) and the ability of bacteria to modify their direct environment by regulating H2O2 concentrations in their surrounding media. This was shown by the bacteria Pseudomonas aeruginosa degrading ~ 18 µM background H2O2 in LB-broth. We also discuss advantages and current limitations of the FIA-MDP system, including a discussion of potential cross-sensitivity and interfering chemical species.

Photochemical vs. Bacterial Control of H2O2 Concentration Across a pCO2 Gradient Mesocosm Experiment in the Subtropical North Atlantic

In the surface ocean, microorganisms are both a source of extracellular H2O2 and, via the production of H2O2 destroying enzymes, also one of the main H2O2 sinks. Within microbial communities, H2O2 sources and sinks may be unevenly distributed and thus microbial community structure could influence ambient extracellular H2O2 concentrations. Yet the biogeochemical cycling of H2O2 and other reactive oxygen species (ROS) is rarely investigated at the community level. Here, we present a time series of H2O2 concentrations during a 28-day mesocosm experiment where a pCO2 gradient (400–1,450 μatm) was applied to subtropical North Atlantic waters. Pronounced changes in H2O2 concentration were observed over the duration of the experiment. Initially H2O2 concentrations in all mesocosms were strongly correlated with surface H2O2 concentrations in ambient seawaters outside the mesocosms which ranged from 20 to 92 nM over the experiment duration (Spearman Rank Coefficients 0.79–0.93, p-values 300 nM in some mesocosms (2–6 fold higher than ambient seawaters). The correlation with ambient H2O2 was then no longer significant (p > 0.05) in all treatments. Furthermore, changes in H2O2 could not be correlated with inter-day changes in integrated irradiance. Yet H2O2 concentrations in most mesocosms were inversely correlated with bacterial abundance (negative Spearman Rank Coefficients ranging 0.59–0.94, p-values < 0.001–0.03). Our results therefore suggest that ambient H2O2 concentration can be influenced by microbial community structure with shifts toward high bacterial abundance correlated with low extracellular H2O2 concentrations. We also infer that the nature of mesocosm experiment design, i.e., the enclosure of water within open containers at the ocean surface, can strongly influence extracellular H2O2 concentrations. This has potential chemical and biological implications during incubation experiments due to the role of H2O2 as both a stressor to microbial functioning and a reactive component involved in the cycling of numerous chemical species including, for example, trace metals and haloalkanes.

Gold Nanocluster Containing Polymeric Microcapsules for Intracellular Ratiometric Fluorescence Biosensing.

A new approach to sensing and imaging hydrogen peroxide (H2O2) was developed using microcapsule-based dual-emission ratiometric luminescent biosensors. Bovine serum albumin-capped gold nanoclusters (BSA-AuNCs) sensitive to H2O2 were coencapsulated with insensitive FluoSpheres (FSs) within polymeric capsules fabricated via the layer-by-layer method. Under single-wavelength excitation, the microcapsule-based biosensors exhibited emission bands at ∼516 and ∼682 nm resulting from the FSs and BSA-AuNCs, respectively. The polyelectrolyte multilayers lining the microcapsules were effective in protecting BSA-AuNCs from the degradation catalyzed by proteases (chymotrypsin, trypsin, papain, and proteinase K) and subsequent luminescent quenching, overcoming a key limitation of prior BSA-AuNC-based sensing systems. The luminescent response of the sensors was also found to be independent of local changes in pH (5–9). Quenching of the AuNCs in the presence of H2O2 enabled the spectroscopic quantification and imaging of changes in H2O2 concentration from 0 to 1 mM. The microcapsule sensors were easily phagocytized by murine macrophage cells (RAW 264.7), were effective as intracellular H2O2 imaging probes, and were successfully used to detect local release of H2O2 in response to an external chemical stimulus.

Sensing and Degradation of Chlorpyrifos by using Environmental Friendly Nano Materials

The nanoparticles of gold and cadmium tellurium quantum dot (CdTe QD) are effective systems for the detection and quantitative removal of chlorpyrifos which is a commonly used pesticide found in surface water of developing nations. Gold nanoparticles coated with citrate changes its color from pink to purple in the presence of chlorpyrifos. Unique CdTe QDs were developed and functionalized by using glucose oxidase for detection of chlorpyrifos. Change in absorbance related to the change in H2O2 concentration. In the solution phase, chlorpyrifos adsorb onto the CdTe QDs surface. During this prolonged interaction, change in color takes place and adsorbed chlorpyrifos becomes precipitated. Thus complete removal of this chlorpyrifos occurs when contaminated water is passed over different CdTe QDs supported on some surface such as alumina. We believe that this method has great potential in the purification of drinking water using gold and CdTe QD nanoparticles.

Dynamics of hydrogen peroxide in a coral reef: Sources and sinks

AbstractThe dynamics of hydrogen peroxide (H2O2) was studied in the fringing coral reef off the coast of Eilat, Red Sea. Diurnal changes in H2O2 concentrations in the reef lagoon were typical of photochemically produced species. During the daytime H2O2 accumulated in the lagoon at low tide and exceeded open water concentrations by 100–250 nM. Elevated H2O2 decay kinetics (termed hereafter antioxidant activity) were also recorded in the lagoon at low tide. The observed antioxidant activities were high enough to moderate H2O2 accumulation in the lagoon. In pursuit of the antioxidant source, the ability of corals to release antioxidant activity to their surrounding water was examined in both natural and laboratory settings. Water collected in situ from surfaces of individual corals and next to a coral knoll contained high antioxidant activity. Incubation experiments revealed that many Red Sea corals release antioxidant activity to their external milieu. Besides serving a potential antioxidant source to the reef system, the antioxidant activity detected on coral surfaces enabled corals to lower H2O2 concentrations in their vicinity. The ability of corals to offset exogenous H2O2 was validated in incubations with Stylophora pistillata in the absence of mixing. Conversely, corals subjected to mixing in a beaker were found to release H2O2, implying that corals may act as both a sink and a source for H2O2 in the reef. This newly described ability of corals to change H2O2 dynamics by releasing both H2O2 and antioxidants may bare important implications for coral physiology and interactions with the environment.

H2O2 Kill Assays of Biofilm Bacteria

Ubiquitous in nature and often surface associated, biofilms cause numerous chronic human infections. Biofilms are structured multicellular bacterial communities where cells are entrapped in a polymer matrix. Bacteria growing as biofilms are characterized by marked tolerance to many biocides, including oxidants such as hydrogen peroxide. Hydrogen peroxide is both produced by host phagocytic cells, and used as an antimicrobial compound. Understanding biofilm tolerance to hydrogen peroxide is therefore relevant to the persistence of Pseudomonas aeruginosa in human infections (such as chronic Pseudomonas aeruginosa infections in cystic fibrosis airways) as well as in environmental settings (such as water pipes). This protocol was developed to determine the tolerance of Pseudomonas aeruginosa biofilms to hydrogen peroxide (H2O2) killing. The bacteria are grown as colony biofilms on polycarbonate membranes, as previously described in Walters et al. 2003. The protocol may be adapted for other bacterial, with appropriate changes in H2O2 concentrations, since different bacterial species may be more or less susceptible to H2O2 than Pseudomonas aeruginosa.

Electrochemical detection of extracellular hydrogen peroxide in Arabidopsis thaliana: a real‐time marker of oxidative stress

An electrochemical approach to directly measure the dynamic process of H2 O2 release from cultures of Arabidopsis thaliana cells is reported. This approach is based on H2 O2 oxidation on a Pt electrode in conjunction with continuous measurement of sample pH. For [H2 O2 ] <1 mm, calibration plots were linear and the amperometric response of the electrode was maximum at pH 6. At higher concentrations ([H2 O2 ] >1 mm), the amperometric response can be described by Michaelian-type kinetics and a mathematical expression relating current intensity and pH was obtained to quantitatively determine H2 O2 concentration. At pH 5.5, the detection limit of the sensor was 3.1 µm (S/N = 3), with a response sensitivity of 0.16 Am(-1 ) cm(-2) and reproducibility was within 6.1% in the range 1-5 × 10(-3 ) m (n = 5). Cell suspensions under normal physiological conditions had a pH between 5.5-5.7 and H2 O2 concentrations in the range 7.0-20.5 µm (n = 5). The addition of exogenous H2 O2 , as well as other potential stress stimuli, was made to the cells and the change in H2 O2 concentration was monitored. This real-time quantitative H2 O2 analysis is a potential marker for the evaluation of oxidative stress in plant cell cultures.

Origin of hydrogen peroxide during the cowpea- Xanthomonas interaction

To assay hydrogen peroxide (H2O2) production by phytopathogenic bacteria in vivo, cowpea seedlings were inoculated using wild-type Xanthomonas campestris pv. phaseoli and its mutant strain on ahpC (with attenuated H2O2 production). Antibiotic rifampicin (Rif) was used to kill off the Xanthomonas campestris pv. phaseoli in cowpea leaves. The optimal concentration of Rif to eradicate the bacteria was 500 μg mL–1, and duration of the Rif treatment to eradicate the bacteria in the cowpea tissues was 48 h. This level of Rif did not significantly affect chloroplast and mitochondrial function in cowpea leaves. The concentration of H2O2 in cowpea inoculated with wild-type or mutant strain of Xanthomonas campestris pv. phaseoli following Rif treatment was measured. Increased H2O2 accumulation was observed in cowpea leaves respectively inoculated with wild-type and mutant strain. The accumulation of excess H2O2 was significantly decreased by the Rif treatment on cowpea wild-type bacteria systems. However, the level of H2O2 in cowpea leaves inoculated with mutant strains following Rif treatment was at the same level as in plant leaves without Rif treatment. The results demonstrate that the change in H2O2 concentration observed in vivo was caused by wild-type bacteria.

Sulfonate-based fluorescent probes for imaging hydrogen peroxide in living cells

Based on the mechanism of H2O2-mediated hydrolysis of sulfonates, two fluorescein disulfonates compounds (FS-1 and FS-2) were designed and synthesized as the highly selective and sensitive fluorescent probes for imaging H2O2 in living cells. The probes were detected with elemental analysis, IR, 1H NMR and 13C NMR. Upon reaction with H2O2, the probes exhibit strong fluorescence responses and high selectivity for H2O2 over other reactive oxygen species and some biological compounds. Furthermore, the sulfonate-based probes, as novel fluorescent reagents, are cell-permeable and can detect micromolar changes in H2O2 concentrations in living cells by using confocal microscopy.

Hydrogen peroxide is involved in the acclimation of the Mediterranean shrub, Cistus albidus L., to summer drought.

This study evaluated the possible role of hydrogen peroxide (H2O2) in the acclimation of a Mediterranean shrub, Cistus albidus L., to summer drought growing under Mediterranean field conditions. For this purpose, changes in H2O2 concentrations and localization throughout a year were analysed. H2O2 changes in response to environmental conditions in parallel with changes in abscisic acid (ABA) and oxidative stress markers, together with lignin accumulation, xylem and sclerenchyma differentiation, and leaf area were also investigated. During the summer drought, leaf H2O2 concentrations increased 11-fold, reaching values of 10 μmol g−1 dry weight (DW). This increase occurred mainly in mesophyll cell walls, xylem vessels, and sclerenchyma cells in the differentiation stage. An increase in ABA levels preceded that of H2O2, but both peaked at the same time in conditions of prolonged stress. C. albidus plants tolerated high concentrations of H2O2 because of its localization in the apoplast of mesophyll cells, xylem vessels, and in differentiating sclerenchyma cells. The increase in ABA, and consequently of H2O2, in plants subjected to drought stress might induce a 3.5-fold increase in ascorbic acid (AA), which maintained and even decreased its oxidative status, thus protecting plants from oxidative damage. After recovery from drought following late-summer and autumn rainfall, a decrease in ABA, H2O2, and AA to their basal levels (∼60 pmol g−1 DW, ∼1 μmol g−1 DW, and ∼20 μmol g−1 DW) was observed.

Boronate-Based Fluorescent Probes for Imaging Cellular Hydrogen Peroxide

The syntheses, properties, and biological applications of the Peroxysensor family, a new class of fluorescent probes for hydrogen peroxide, are presented. These reagents utilize a boronate deprotection mechanism to provide high selectivity and optical dynamic range for detecting H2O2 in aqueous solution over similar reactive oxygen species (ROS) including superoxide, nitric oxide, tert-butyl hydroperoxide, hypochlorite, singlet oxygen, ozone, and hydroxyl radical. Peroxyresorufin-1 (PR1), Peroxyfluor-1 (PF1), and Peroxyxanthone-1 (PX1) are first-generation probes that respond to H2O2 by an increase in red, green, and blue fluorescence, respectively. The boronate dyes are cell-permeable and can detect micromolar changes in H2O2 concentrations in living cells, including hippocampal neurons, using confocal microscopy and two-photon microscopy. The unique combination of ROS selectivity, membrane permeability, and a range of available excitation/emission colors establishes the potential value of PR1, PF1, PX1, and related probes for interrogating the physiology and pathology of cellular H2O2.

The annual cycle of hydrogen peroxide: an indicator of chemical instability?

Abstract. A box model has been used to study the annual cycle in hydrogen peroxide concentrations with the objective of determining whether the observed difference in summer and winter values reflects instability in the underlying photochemistry. The model is run in both steady-state and time-dependent modes. The steady-state calculations show that, for some range of NOx background levels, two stable solutions to the continuity equations exist for a period of days in spring and fall. The corresponding time-dependent model indicates that, for sufficiently high background NOx concentrations, the spring and fall changes in H2O2 concentration may be interpreted as a forced transition between the two underlying stable regimes. The spring transition is more rapid than that in fall, an asymmetry that becomes more marked as background NOx increases. This asymmetry is related to the different time scales involved in chemical production and loss of H2O2. Observations of the spring increase in H2O2 concentration may therefore provide a better measure of the change in the underlying chemical regime than does the fall decrease. The model results developed in this paper will be compared with two sets of observations that cover annual variations of peroxide concentrations under different background pollution conditions.