Manganese Oxide/Hemin-Functionalized Graphene as a Platform for Peroxynitrite Sensing

Peroxynitrite (ONOO−, PON) is a powerful oxidizing agent generated in vivo by the diffusion-limited reaction of nitric oxide (NO) and superoxide (O2˙−) radicals. Under oxidative stress, cumulated peroxynitrite levels are associated with chronic inflammatory disorders and other pathophysiological conditions. The accurate detection of peroxynitrite in biological systems is important, not only to understand the genesis and development of diseases, but also to explore and design potential therapeutics. Herein, a manganese oxide/hemin-modified graphene interface is explored as a platform for peroxynitrite amperometric detection. Hemin-functionalized reduced graphene oxide was further modified with manganese oxide nanoparticles to provide a composite material with catalytic activity toward the electrochemical oxidation of peroxynitrite. The morphology of the composite material was characterized using scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, and UV-Vis absorption measurements. We investigated the electrocatalytic oxidation of peroxynitrite on graphite electrodes modified with the composite material using cyclic voltammetry and amperometry. The results showed that the incorporation of manganese oxide nanoparticles into graphene/hemin material enhances the catalytic detection of peroxynitrite compared to graphene/hemin alone

Synthetic Melanin Films as Potential Interfaces for Peroxynitrite Detection and Quantification

Peroxynitrite (PON) is a highly reactive oxygen-nitrogen species that facilitates both oxidation and nitration reactions. Early reports have revealed the deleterious effects of PON on DNA, proteins, and lipids. Recent studies have suggested that melanin can act as an antioxidative therapy to scavenge the reactive oxygen-nitrogen species (RO-NS) including PON. Melanin is a natural pigment that has many physiological functions involving the neutralization of highly oxidative species. In this project, the interaction between PON and synthetic melanin has been studied. In addition, the electrochemical characteristics of the polymerized 5,6-dihydroxy indole (DHI) as a model of synthetic melanin were examined using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The ultraviolet-visible (UV-Vis) spectroscopy showed a significant difference in the absorbance of PON alone and in the presence of melanin films. Finally, we report on the possibility of using the DHI-melanin film as a platform for the quantitative detection of PON in solutions

Synthesis and Characterization of Cobalt(II) N,N′‑Diphenylazodioxide Complexes

Removal of chloride from CoCl2 with TlPF6 in acetonitrile, followed by addition of excess nitrosobenzene, yielded the eight-coordinate cobalt(II) complex salt [Co{Ph(O)NN(O)- Ph}4](PF6)2, shown by single-crystal X-ray analysis to have a distorted tetragonal geometry. The analogous treatment of the bipyridyl complex Co(bpy)Cl2 yielded the mixed-ligand cobalt(II) complex salt [Co(bpy){Ph(O)NN(O)Ph}2](PF6)2, whose singlecrystal X-ray structure displays a trigonal prismatic geometry, similar to that of the iron(II) cation in the previously known complex salt [Fe{Ph(O)NN(O)Ph}3](FeCl4)2. The use of TlPF6 to generate solvated metal complex cations from chloride salts or chlorido complexes, followed by the addition of nitrosobenzene, is shown to be a useful synthetic strategy for the preparation of azodioxide complex cations with the noncoordinating, diamagnetic PF6 − counteranion. Coordination number appears to be more important than d electron count in determining the geometry and metal−ligand bond distances of diphenylazodioxide complexes

Nanomaterials-based Sensors for Peroxynitrite Detection and Quantification

Peroxynitrite (ONOO-, PON) plays a crucial role in several cardiovascular dysfunctions and other diseases triggered by oxidative stress. PON is a strong oxidizing agent produced from the diffusion-controlled reaction between nitric oxide radical and superoxide anion-radical. It is also a member of the reactive oxygen-nitrogen species family, which attacks vital components inside the body and initiates deleterious effects via direct and indirect interactions. PON reacts directly with lipids, DNA, and proteins, whereas indirectly, it acts as an initiator of radical-chain reactions. In this work, we have explored various interfaces of manganese-oxide-decorated graphene/hemin and selenium-containing compound for PON detection and quantification. The combination of manganese oxide nanoparticles with the graphene/hemin matrix has allowed for more hemin molecules to be adsorbed on the final composite matrix. As a result, the adsorbed hemin has enhanced the catalytic activity of the final composite and improved the sensitivity towards PON detection. In the same context, a selenium-containing compound (aniline-selenide) has been synthesized and grafted on the electrode surface using the chemistry of diazonium salt. The aniline-selenide-modified electrode showed an increase of approximately 40 times the catalytic current as the aniline-modified electrode. Throughout this project, the preparation methods of the electroactive nanomaterials were described in detail. Moreover, the characterizations of the prepared-materials have been investigated by various physicochemical methods using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet/visible measurements (UV/Vis), and X-ray photoelectron spectroscopy (XPS). This study showed the importance of using selenium and manganese interfaces as sensitive platforms for PON detection. It also provides the initial stage to extend the use of these interfaces to ultramicroelectrodes sensors for use at the level of single cells

Nanomaterials-based Sensors for Peroxynitrite Detection and Quantification

Peroxynitrite (ONOO-, PON) plays a crucial role in several cardiovascular dysfunctions and other diseases triggered by oxidative stress. PON is a strong oxidizing agent produced from the diffusion-controlled reaction between nitric oxide radical and superoxide anion-radical. It is also a member of the reactive oxygen-nitrogen species family, which attacks vital components inside the body and initiates deleterious effects via direct and indirect interactions. PON reacts directly with lipids, DNA, and proteins, whereas indirectly, it acts as an initiator of radical-chain reactions. In this work, we have explored various interfaces of manganese-oxide-decorated graphene/hemin and selenium-containing compound for PON detection and quantification. The combination of manganese oxide nanoparticles with the graphene/hemin matrix has allowed for more hemin molecules to be adsorbed on the final composite matrix. As a result, the adsorbed hemin has enhanced the catalytic activity of the final composite and improved the sensitivity towards PON detection. In the same context, a selenium-containing compound (aniline-selenide) has been synthesized and grafted on the electrode surface using the chemistry of diazonium salt. The aniline-selenide-modified electrode showed an increase of approximately 40 times the catalytic current as the aniline-modified electrode. Throughout this project, the preparation methods of the electroactive nanomaterials were described in detail. Moreover, the characterizations of the prepared-materials have been investigated by various physicochemical methods using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet/visible measurements (UV/Vis), and X-ray photoelectron spectroscopy (XPS). This study showed the importance of using selenium and manganese interfaces as sensitive platforms for PON detection. It also provides the initial stage to extend the use of these interfaces to ultramicroelectrodes sensors for use at the level of single cells

Manganese Functionalized Graphene As a New Platform for Peroxynitrite Sensing

Peroxynitrite (PON, ONOO−) is a powerful oxidizing agent generated in vivo by the diffusion-controlled reaction of nitric oxide (·NO) and superoxide (O2·−) radicals. Peroxynitrite levels accumulate under oxidative stress. Elevated peroxynitrite levels are associated with chronic inflammatory disorders including neurological and vascular diseases, as well as a number of other pathophysiological conditions. The accurate detection of this analyte in biological systems is of paramount importance, not only to understand the genesis and causes of ailment at the tissue/cellular level, but also to suggest and design potential therapeutic routes. In the past, we studied the sensitivity of carbon electrodes modified by polymerized hemin (iron protoporphyrin) as standalone and in combination with conductive polymer PEDOT (3,4-ethylendioxythiophene). These polymerized surfaces have been used as platforms for amperometric measurements of peroxynitrite both in still solutions and under flow conditions. More recently, we extended this line of research to the use of hemin functionalized graphene as a catalytic platform for PON oxidative detection. In this work we explored and discussed the sensitivity of manganese-based interfaces for peroxynitrite amperometric determination. Surfaces of electrodeposited manganese (Mn), manganese-graphene, and manganese-decorated graphene/hemin-based nanostructures were formed on glassy carbon electrodes as well as on carbon fiber microelectrodes. The effect of graphene on the electrodeposition of Mn was investigated by cyclic voltammetry. We tested these interfaces for electro-catalytic sensing of peroxynitrite in solution using chronoamperometric technique. The morphology of the prepared manganese interfaces was characterized using scanning electron microscopy (SEM), Energy Dispersive X-ray Analysis (EDXA), Ultra-Violet/Visible (UV/Vis), X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. The results showed that manganese-functionalized hemin/graphene enhances peroxynitrite detection and quantification compared to hemin/graphene-only interfaces. We noticed that there is a synergistic effect of the presence of graphene with manganese nanoparticles in the prepared materials. We compared and contrasted on how graphene nano-sheets affect the electrochemical behavior of hemin-modified electrodes in the absence and presence of manganese nanoparticles. In conclusion, we found that the incorporation of manganese influences the sensitivity of PON-sensing hemin/graphene platforms

Manganese Functionalized Graphene As a New Platform for Peroxynitrite Sensing

Peroxynitrite (PON, ONOO−) is a powerful oxidizing agent generated in vivo by the diffusion-controlled reaction of nitric oxide (·NO) and superoxide (O2·−) radicals. Peroxynitrite levels accumulate under oxidative stress. Elevated peroxynitrite levels are associated with chronic inflammatory disorders including neurological and vascular diseases, as well as a number of other pathophysiological conditions. The accurate detection of this analyte in biological systems is of paramount importance, not only to understand the genesis and causes of ailment at the tissue/cellular level, but also to suggest and design potential therapeutic routes. In the past, we studied the sensitivity of carbon electrodes modified by polymerized hemin (iron protoporphyrin) as standalone and in combination with conductive polymer PEDOT (3,4-ethylendioxythiophene). These polymerized surfaces have been used as platforms for amperometric measurements of peroxynitrite both in still solutions and under flow conditions. More recently, we extended this line of research to the use of hemin functionalized graphene as a catalytic platform for PON oxidative detection. In this work we explored and discussed the sensitivity of manganese-based interfaces for peroxynitrite amperometric determination. Surfaces of electrodeposited manganese (Mn), manganese-graphene, and manganese-decorated graphene/hemin-based nanostructures were formed on glassy carbon electrodes as well as on carbon fiber microelectrodes. The effect of graphene on the electrodeposition of Mn was investigated by cyclic voltammetry. We tested these interfaces for electro-catalytic sensing of peroxynitrite in solution using chronoamperometric technique. The morphology of the prepared manganese interfaces was characterized using scanning electron microscopy (SEM), Energy Dispersive X-ray Analysis (EDXA), Ultra-Violet/Visible (UV/Vis), X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy. The results showed that manganese-functionalized hemin/graphene enhances peroxynitrite detection and quantification compared to hemin/graphene-only interfaces. We noticed that there is a synergistic effect of the presence of graphene with manganese nanoparticles in the prepared materials. We compared and contrasted on how graphene nano-sheets affect the electrochemical behavior of hemin-modified electrodes in the absence and presence of manganese nanoparticles. In conclusion, we found that the incorporation of manganese influences the sensitivity of PON-sensing hemin/graphene platforms

Peroxynitrite Sensing: From Graphene-Based Platforms to Modified Boron-Doped Diamond Electrodes

Peroxynitrite (PON) is a major cytotoxic agent, implicated in a host of pathophysiological conditions. In biological systems, peroxynitrite is the primary product of the reaction of superoxide ion and nitric oxide, and has been lately at the forefront of investigations dealing with nitroxidative stress. One major challenge in the analytical determination of peroxynitrite under physiologic conditions is its short half-life and its fast reactivity with many cellular targets. Spectroscopic and other detection methods for peroxynitrite have been proposed but face the problem of real-time quantification and particularly when localized measurements are needed. We have shown that catalyzed electrochemical detection of peroxynitrite is a simpler and more convenient technique. In the past, we described the use of polymerized hemin (iron protoporphyrin IX) and other porphyrins on graphite electrodes as platforms for amperometric measurement of peroxynitrite both in still solutions and under flow conditions. This work has been extended to reduced graphene oxide functionalized with hemin as a catalytic platform for PON oxidative detection. Boron-doped diamond electrodes (BDD) have been used as platforms for electrochemical detection of a number of analytes in environmental samples as well as in biological media. BDD electrodes have the advantage to provide a relatively wide electrochemical window as well as low capacitive currents. In the present paper we compare and contrast the direct electrochemical oxidation of peroxynitrite on BDD and the catalytic oxidation of PON on modified diamond electrodes as potential sensing platforms of PON. Boron-doped diamond based microarray electrodes have been proposed as potential devices for neuronal stimulation. We hypothesize that PON generated at the array-tissue interface is a major cytotoxic intermediate leading to ultimate tissue death. Developing sensing electrodes based on catalytic detection of PON on boron-doped diamond electrodes is a step towards using individually addressable electrodes in a BDD electrode array for both electrical stimulation and monitoring of PON levels as a predictor of tissue deterioration and, ultimately, death. Understanding the fundamental processes involved during the catalytic oxidation of PON on modified BDD offers the possibility to fine-tune the surface to optimize PON detection

Selenium-Decorated Graphene for Peroxynitrite Detection

Peroxynitrite (PON, ONOO−) is a member of the reactive oxygen-nitrogen species family. PON is generated in vivo by the diffusion-limited reaction (~2×1010 M−1S−1) of nitric oxide (·NO) and superoxide (O2·−) radicals. Elevated peroxynitrite levels are associated with several human pathologies, such as arthritis, inflammation, and carcinogenesis, as well as ageing-associated diseases. Thus, the precise detection of this species in biological systems is crucial, not only to understand the genesis and causes of ailments at the tissue/cellular level, but also to suggest and design potential therapies. The essential trace element selenium (Se) is the catalytic cofactor of important endogenous antioxidative systems of the human body. In the past decade, selenium attracted the attention of many research groups for the understanding of fundamental biological functions and biomimetic applications. Selenium is found in several human proteins (selenoproteins), many of them involved in anti-oxidant defense systems. Therefore, selenium plays a key role in redox regulation as a modulator of reactive oxygen species (ROS). Recently, a number of novel synthetic organoselenium compounds has been prepared and used as antioxidants in medicinal chemistry such as ebselen. In this work, we prepare and investigate interfaces based on the electrochemical deposition of selenium nanoparticles. We prepared surfaces of electrodeposited elemental selenium (Se) and selenium-decorated graphene-based nanostructures on glassy carbon electrodes and carbon fiber microelectrodes. We have used several physicochemical methods to characterize these PON-sensitive interfaces, including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX), X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, and UV-vis on ITO transparent electrodes. We tested these interfaces for electrocatalytic sensing of peroxynitrite. We found that selenium-modified graphene platform is sensitive to peroxynitrite in solution, and it provides a viable interface for electrochemical sensing of this analyte. We observed that there is a synergistic effect of the presence of graphene as a substrate for selenium nanoparticles in the electrocatalytic detection of PON. In this paper, we will present our findings using this new PON-sensitive interface. We will compare and contrast the performance of the various modified carbon electrodes in terms of PON sensitivity using cyclic voltammetry and dose-response chronoamperometry

Selenium-Decorated Graphene for Peroxynitrite Detection

Peroxynitrite (PON, ONOO−) is a member of the reactive oxygen-nitrogen species family. PON is generated in vivo by the diffusion-limited reaction (~2×1010 M−1S−1) of nitric oxide (·NO) and superoxide (O2·−) radicals. Elevated peroxynitrite levels are associated with several human pathologies, such as arthritis, inflammation, and carcinogenesis, as well as ageing-associated diseases. Thus, the precise detection of this species in biological systems is crucial, not only to understand the genesis and causes of ailments at the tissue/cellular level, but also to suggest and design potential therapies. The essential trace element selenium (Se) is the catalytic cofactor of important endogenous antioxidative systems of the human body. In the past decade, selenium attracted the attention of many research groups for the understanding of fundamental biological functions and biomimetic applications. Selenium is found in several human proteins (selenoproteins), many of them involved in anti-oxidant defense systems. Therefore, selenium plays a key role in redox regulation as a modulator of reactive oxygen species (ROS). Recently, a number of novel synthetic organoselenium compounds has been prepared and used as antioxidants in medicinal chemistry such as ebselen. In this work, we prepare and investigate interfaces based on the electrochemical deposition of selenium nanoparticles. We prepared surfaces of electrodeposited elemental selenium (Se) and selenium-decorated graphene-based nanostructures on glassy carbon electrodes and carbon fiber microelectrodes. We have used several physicochemical methods to characterize these PON-sensitive interfaces, including Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDX), X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, and UV-vis on ITO transparent electrodes. We tested these interfaces for electrocatalytic sensing of peroxynitrite. We found that selenium-modified graphene platform is sensitive to peroxynitrite in solution, and it provides a viable interface for electrochemical sensing of this analyte. We observed that there is a synergistic effect of the presence of graphene as a substrate for selenium nanoparticles in the electrocatalytic detection of PON. In this paper, we will present our findings using this new PON-sensitive interface. We will compare and contrast the performance of the various modified carbon electrodes in terms of PON sensitivity using cyclic voltammetry and dose-response chronoamperometry