Electropolymerized manganese porphyrin/polypyrrole films as catalytic surfaces for the oxidation of nitric oxide

Orientational Effects and Molecular-Scale Thermoelectricity Control

The orientational effect concept in a molecular-scale junction is established for asymmetric junctions, which requires the fulfillment of two conditions: (1) design of an asymmetric molecule with strong distinct terminal end groups and (2) construction of a doubly asymmetric junction by placing an asymmetric molecule in an asymmetric junction to form a multicomponent system such as Au/Zn-TPP+M/Au. Here, we demonstrate that molecular-scale junctions that satisfy the conditions of these effects can manifest Seebeck coefficients whose sign fluctuates depending on the orientation of the molecule within the asymmetric junction in a complete theoretical investigation. Three anthracene-based compounds are investigated in three different scenarios, one of which displays a bithermoelectric behavior due to the presence of strong anchor groups, including pyridyl and thioacetate. This bithermoelectricity demonstration implies that if molecules with alternating orientations can be placed between an asymmetric source and drain, they can be potentially utilized for increasing the thermovoltage in molecular-scale thermoelectric energy generators (TEGs).

Electrochemical Detection of Gasotransmitters: Status and Roadmap

Gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), are a class of gaseous, endogenous signaling molecules that interact with one another in the regulation of critical cardiovascular, immune, and neurological processes. The development of analytical sensing mechanisms for gasotransmitters, especially multianalyte mechanisms, holds vast importance and constitutes a growing area of study. This review provides an overview of electrochemical sensing mechanisms with an emphasis on opportunities in multianalyte sensing. Electrochemical methods demonstrate good sensitivity, adequate selectivity, and the most well-developed potential for the multianalyte detection of gasotransmitters. Future research will likely address challenges with sensor stability and biocompatibility (i.e., sensor lifetime and cytotoxicity), sensor miniaturization, and multianalyte detection in biological settings.

In Vitro Monitoring of Nitric Oxide Release in the Mouse Colon Using a Boron-Doped Diamond Microelectrode Modified with Platinum Nanoparticles and Nafion

This research reports on the preparation of a boron-doped diamond microelectrode modified with platinum nanoparticles and Nafion and its application for detecting nitric oxide (NO) in vitro in the mouse colon. Platinum nanoparticle deposition was performed potentiodynamically using a 2.0 mmol L^-1 potassium hexachloroplatinate solution and cycling from -0.2 to 1.3 V vs Ag/AgCl at 0.01 V s^-1 for 10 cycles. The Nafion overlayer was applied by immersion in a solution containing 2.5% (w/v) colloidal Nafion and drying overnight at 55 °C in a humid environment. The optimal microelectrode preparation conditions were chosen based on the electrode response for NO oxidation as well as rejection of nitrite (NO₂^-) oxidation, the main interferent in the electrochemical detection of NO in biological media. Detection figures of merit include a sensitivity of 16.7 ± 2.7 mA M^-1 cm^-2 (n = 3 electrodes), a detection limit of 0.5 μmol L^-1 (S/N = 3), and an electrode response reproducibility of 2.5% (RSD). Electrical stimulation and continuous amperometry were used to measure NO release from myenteric ganglia in wild-type male and female mice in response to an increasing number of electrical stimuli to study nitrergic signaling in the colon. We also present preliminary data regarding the use of optogenetics to selectively stimulate nitrergic myenteric neurons using blue light stimulation with a goal of understanding how inhibitory neuromuscular signaling is involved in the myenteric plexus circuitry that controls intestinal motility.

Differential lethal and sublethal effects in embryonic zebrafish exposed to different sizes of silver nanoparticles

Various parameters can influence the toxic response to silver nanoparticles (Ag NPs), including the size and surface properties, as well as the exposure environment and the biological site of action. Herein, we assess the intestinal toxicity of three different sizes (10, 40, and 100 nm) of Ag NPs in embryonic zebrafish, and describe the relationship between the properties and behavior of Ag NPs in the exposure medium, and induction of lethal and sublethal effects. We find that the composition of the medium and the size contribute to differential NPs agglomeration, release of Ag ions, and subsequent effects during exposure. The exposure medium causes dramatic reduction in silver dissolution due to the presence of salts and divalent cations, which limits the lethal potential of silver ions. Lethality is observed primarily for embryos exposed to medium sized Ag NPs (40 nm), but not to the supernatant originated from particles, which suggests that the exposure to particulate silver is the main cause of mortality. On the other hand, the exposure to 10 nm and 100 nm NPs, as well as Ag ions, only causes sublethal developmental defects in skeletal muscles and intestine, and induces a nitric oxide imbalance.

A Reactive Oxygen/Nitrogen Species Sensor Fabricated from an Electrode Modified with a Polymerized Iron Porphyrin and a Polymer Electrolyte Membrane

We have developed an electrochemical reactive oxygen/nitrogen species sensor that can detect superoxide anion radicals (O₂^-•) and nitric oxide (NO). The reactive oxygen/nitrogen species sensor was fabricated by surface modification of an electrode with polymerized iron tetrakis(3-thienyl)porphyrin (FeT3ThP), and it can detect either O₂^-• or NO by switching the applied potential. Furthermore, we fabricated a sensor with improved selectivity by coating a Nafion^® film onto the poly(FeT3ThP)-modified electrode. An interference current caused by NO₂^- was seen for the poly(FeT3ThP)-modified electrode, while the interference current was significantly reduced at the Nafion^®/poly(FeT3ThP)-modified electrode, leading to improved selectivity for NO detection. The current response at the Nafion^®/poly(FeT3ThP)-modified electrode exhibited good linearity in the O₂^-• and NO concentration ranges 1.3 - 4.1, and 0.5 - 10 μM, respectively. The Nafion^®/poly(FeT3ThP)-modified and poly(FeT3ThP)-modified electrodes are highly versatile, because these electrodes can detect either O₂^-• or NO by switching the applied potential. Since the Nafion^®/poly(FeT3ThP)-modified and poly(FeT3ThP)-modified electrodes contain no bio-derived compounds, the reactive oxygen/nitrogen species sensor should be safe even when it is used in vivo.

A sensitive acupuncture needle microsensor for real-time monitoring of nitric oxide in acupoints of rats

This study reports an acupuncture needle modified with an iron-porphyrin functionalized graphene composite (FGPC) for real-time monitoring of nitric oxide (NO) release in acupoints of rats. A gold film was first deposited to the needle surface to enhance the conductivity. The FGPC was prepared via hydrothermal synthesis, and subsequently applied to the tip surface of acupuncture needle by electrochemical deposition method. The functionalized needle enabled a specific and sensitive detection of NO based on the favorably catalytic properties of iron-porphyrin and the excellent conductivity of graphene. Amperometric data showed that the needle achieved not only a low detection limit down to 3.2 nM in PBS solution, but also a satisfactory selectivity. Interestingly, the functionalized needle could be inserted into the acupoints of rats for real-time monitoring of NO in vivo. It was found that a remarkable response to NO was respectively obtained in different acupoints when stimulated by _L-arginine (_L-Arg), revealing that the release of NO was detectable in acupoints. We expect this work would showcase the applications of acupuncture needle in detecting some important signaling molecules in vivo, and exploring the mechanism of acupuncture treatment.

Electrochemical Behavior and Voltammetric Determination of a Manganese(II) Complex at a Carbon Paste Electrode

Investigation of the electrochemical behavior using cyclic voltammetry and detection of [Mn(2+)(thiophenyl-2-carboxylic acid)2 (triethanolamine)] with adsorptive stripping differential pulse voltammetry. The electrochemical behavior of a manganese(II) complex [Mn(2+)(thiophenyl-2-carboxylic acid)2(triethanolamine)] (A) was investigated using cyclic and differential pulse voltammetry in an acetate buffer of pH 4.6 at a carbon paste electrode. Further, an oxidation-reduction mechanism was proposed. Meanwhile, an adsorptive stripping differential pulse voltammetric method was developed for the determination of manganese(II) complex.

Application of a nitric oxide sensor in biomedicine

In the present study, we describe the biochemical properties and effects of nitric oxide (NO) in intact and dysfunctional arterial and venous endothelium. Application of the NO electrochemical sensor in vivo and in vitro in erythrocytes of healthy subjects and patients with vascular disease are reviewed. The electrochemical NO sensor device applied to human umbilical venous endothelial cells (HUVECs) and the description of others NO types of sensors are also mentioned.

Comparative evaluation of intestinal nitric oxide in embryonic zebrafish exposed to metal oxide nanoparticles

Nanoparticle (NP) exposure may induce oxidative stress through generation of reactive oxygen and nitrogen species, which can lead to cellular and tissue damage. The digestive system is one of the initial organs affected by NP exposure. Here, it is demonstrated that exposure to metal oxide NPs induces differential changes in zebrafish intestinal NO concentrations. Intestinal NO concentrations are quantified electrochemically with a carbon fiber microelectrode inserted in the intestine of live embryos. Specificity of the electrochemical signals is demonstrated by NO-specific pharmacological manipulations and the results are correlated with the 4,5-diaminofluorescein-diacetate (DAF-FM-DA). NPs are demonstrated to either induce or reduce physiological NO levels depending on their redox reactivity, type and dose. NO level is altered following exposure of zebrafish embryos to CuO and CeO2 NPs at various stages and concentrations. CuO NPs increase NO concentration, suggesting an intestinal oxidative damage. In contrast, low CeO2 NP concentration exposure significantly reduces NO levels, suggesting NO scavenging activity. However, high concentration exposure results in increased NO. Alterations in NO concentration suggest changes in intestinal physiology and oxidative stress, which will ultimately correspond to NPs toxicity. This work also demonstrates the use of electrochemistry to monitor in vivo changes of NO within zebrafish organs.

Overview of significant examples of electrochemical sensor arrays designed for detection of nitric oxide and relevant species in a biological environment

Ultramicroelectrode sensor arrays in which each electrode, or groups of electrodes, are individually addressable are of particular interest for detection of several species concomitantly, by using specific sensing chemistry for each analyte, or for mapping of one analyte to achieve spatio-temporal analysis. Microfabrication technology, for example photolitography, is usually used for fabrication of these arrays. The most widespread geometries produced by photolithography are thin-film microdisc electrode arrays with different electrode distributions (square, hexagonal, or random). In this paper we review different electrochemical sensor arrays developed to monitor, in vivo, NO levels produced by cultured cells or sliced tissues. Simultaneous detection of NO and analytes interacting with or released at the same time as NO is also discussed.

Vascular lumen simulation and highly-sensitive nitric oxide detection using three-dimensional gelatin chip coupled to TiC/C nanowire arrays microelectrode

Reproducing the physiological environment of blood vessels for the in vitro investigation of endothelial cell functions is very challenging. Here, we describe a vascular-like structure based on a three-dimensional (3D) gelatin chip with good compatibility and permeability which is also cost-effective and easy to produce. The controllable lumen diameter and wall thickness enable close mimicking of blood vessels in vitro. The 3D gelatin matrix between adjacent lumens is capable of generating soluble-factor gradients inside, and diffusion of molecules with different molecular weights through the matrix is studied. The cultured human umbilical vein endothelial cells proliferate on the gelatin lumen linings to form a vascular lumen. The hemodynamic behavior including adhesion, alignment of endothelial cells (ECs) under shear stress and pulsatile stretch is studied. Furthermore, a microelectrode comprising TiC/C nanowire arrays is fabricated to detect nitric oxide with sub-nM detection limits and NO generation from the cultured ECs is monitored in real time. This vascular model reproduces the surrounding parenchyma of endothelial cells and mimics the hemodynamics inside blood vessels very well, thereby enabling potential direct investigation of hemodynamics, angiogenesis, and tumor metastasis in vitro.

Characterization of electrodes chemically modified with Mn(III) porphyrin/polypyrrole films as catalytic surfaces for an azo dye

In this study we describe the electrochemical behavior of 5,10,15,20-tetrakis(2'-aminophenylporphyrin)manganese(III) chloride supported on a glassy carbon electrode, as well as the electrochemical preparation and characterization of thin films based on pyrrole-3-carboxylic acid. The electrocatalytic action of the electrode modified with the Mn(III) porphyrin toward an azo dye was tested, and the characteristic strong interaction between the incorporated metalloporphyrin and RR120 dye was verified.

Synthesis, spectral and electrochemical properties of a new family of pyrrole substituted cobalt, iron, manganese, nickel and zinc phthalocyanine complexes

A new family of pyrrole substituted metallophthalocyanine complexes, namely cobalt(II), iron(II), manganese(III), nickel(II) and zinc(II) tetrakis-4-(pyrrol-1-yl)phenoxy phthalocyanines (noted as M ( TPhPyrPc ), where M is the metallic cation) have been synthesized and fully characterized. In particular, the UV-visible spectra of the iron and nickel complexes showed extensive aggregation even at low concentrations. The cyclic voltammetry of the cobalt, iron and manganese complexes showed three to four redox couples assigned to metal and ring based processes. Spectroelectrochemistry of the manganese derivative confirmed that the synthesized complex is Mn III( TPhPyrPc -2) and that the reduction of Mn II( TPhPyrPc -2) to be centred on the ring and rather than on the metal, forming the Mn II( TPhPyrPc -4) species. Also, the electrochemical polymerization of these newly synthesized pyrrole-substituted phthalocyanines has been demonstrated in the case of the cobalt complex and the electrocatalytic activity of the obtained film has been tested towards the oxidation of L-cysteine.

Polymerization model for hydrogen peroxide initiated synthesis of polypyrrole nanoparticles

A very simple, environmentally friendly, one-step oxidative polymerization route to fabricate polypyrrole (Ppy) nanoparticles of fixed size and morphology was developed and investigated. The herein proposed method is based on the application of sodium dodecyl sulfate and hydrogen peroxide, both easily degradable and cheap materials. The polymerization reaction is performed on 24 h time scale under standard conditions. We monitored a polaronic peak at 465 nm and estimated nanoparticle concentration during various stages of the reaction. Using this data we proposed a mechanism for Ppy nanoparticle formation in accordance with earlier emulsion polymerization mechanisms. Rates of various steps in the polymerization mechanism were accounted for and the resulting particles identified using atomic force microscopy. Application of Ppy nanoparticles prepared by the route presented here seems very promising for biomedical applications where biocompatibility is paramount. In addition, this kind of synthesis could be suitable for the development of solar cells, where very pure and low-cost conducting polymers are required.

Electrochemical nitric oxide sensors for physiological measurements

The important biological roles of nitric oxide (NO) have prompted the development of analytical techniques capable of sensitive and selective detection of NO. Electrochemical sensing, more than any other NO detection method, embodies the parameters necessary for quantifying NO in challenging physiological environments such as blood and the brain. In this tutorial review, we provide a broad overview of the field of electrochemical NO sensors, including design, fabrication, and analytical performance characteristics. Both electrochemical sensors and biological applications are detailed.

Analytical chemistry of nitric oxide

Nitric oxide (NO) is the focus of intense research primarily because of its wide-ranging biological and physiological actions. To understand its origin, activity, and regulation, accurate and precise measurement techniques are needed. Unfortunately, analytical assays for monitoring NO are challenged by NO's unique chemical and physical properties, including its reactivity, rapid diffusion, and short half-life. Moreover, NO concentrations may span the picomolar-to-micromolar range in physiological milieus, requiring techniques with wide dynamic response ranges. Despite such challenges, many analytical techniques have emerged for the detection of NO. Herein, we review the most common spectroscopic and electrochemical methods, with a focus on the underlying mechanism of each technique and on approaches that have been coupled with modern analytical measurement tools to create novel NO sensors.

Fluorinated xerogel-derived microelectrodes for amperometric nitric oxide sensing

An amperometric fluorinated xerogel-derived nitric oxide (NO) microelectrode is described. A range of fluorine-modified xerogel polymers were synthesized via the cohydrolysis and condensation of alkylalkoxy- and fluoroalkoxysilanes. Such polymers were evaluated as NO sensor membranes to identify the optimum composition for maximizing NO permeability while providing sufficient selectivity for NO in the presence of common interfering species. By taking advantage of both the versatility of sol-gel chemistry and the "poly(tetrafluoroethylene)-like" high NO permselective properties of the xerogels, the performance of the fluorinated xerogel-derived sensors was excellent, surpassing all miniaturized NO sensors reported to date. In contrast to previous electrochemical NO sensor designs, xerogel-based NO microsensors were fabricated using a simple, reliable dip-coating procedure. An optimal permselective membrane was achieved by synthesizing xerogels of methyltrimethoxysilane (MTMOS) and 20% (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trimethoxysilane (17FTMS, balance MTMOS) under acid-catalyzed conditions. The resulting NO microelectrode had a conical tip of approximately 20 microm in diameter and approximately 55 microm in length and exhibited sensitivities of 7.91 pA x nM (-1) from 0.2 to 3.0 nM (R (2) = 0.9947) and 7.60 nA x microM (-1) from 0.5 to 4.0 microM ( R (2) = 0.9999), detection limit of 83 pM (S/ N = 3), response time ( t 95%) of <3 s, and selectivity (log K NO, j (amp)) of -5.74, <-6, <-6, <-6, <-6, -5.84, and -1.33 for j = nitrite, ascorbic acid, uric acid, acetaminophen, dopamine, ammonia/ammonium, and carbon monoxide. In addition, the sensor proved functional up to 20 d, maintaining >or=90% of the sensor's initial sensitivity without serious deterioration in selectivity.

Nitric oxide selective electrodes

Since nitric oxide (NO) was identified as the endothelial-derived relaxing factor in the late 1980s, many approaches have attempted to provide an adequate means for measuring physiological levels of NO. Although several techniques have been successful in achieving this aim, the electrochemical method has proved the only technique that can reliably measure physiological levels of NO in vitro, in vivo, and in real time. We describe here the development of electrochemical sensors for NO, including the fabrication of sensors, the detection principle, calibration, detection limits, selectivity, and response time. Furthermore, we look at the many experimental applications where NO selective electrodes have been successfully used.

Sol-gel derived amperometric nitric oxide microsensor

An amperometric sol-gel derived nitric oxide microsensor is described. Several silicon-based xerogel membranes are evaluated to identify the optimum composition for maximizing NO permeability while providing sufficient selectivity for NO in the presence of common interfering species. Xerogel permeability and selectivity are further manipulated as a function of reaction/processing conditions. In addition, the effects of incorporating Nafion into the xerogel matrix on sensor performance and the stability of the ensuing xerogel/Nafion hybrid film are evaluated. The optimal permselective membrane is achieved by catalyzing polycondensation of the xerogel composed of methyltrimethoxysilane and (aminoethylaminomethyl)phenethyltrimethoxysilane and Nafion with NO gas. The resulting NO microsensor exhibits a sensitivity of 0.17 +/-0.02 pA/nM (from 25 to 800 nM, r = 0.9991), detection limit of 25 nM (S/N = 3), response time of 9 s (t(95%), a NO concentration change from 400 to 500 nM), selectivity (log K(NOj) amp) of -5.8, <-6, <-6, and <-6 for j = nitrite, ascorbic acid, uric acid, and acetaminophen, and a lifetime of 8 d (82% of initial sensitivity without serious deterioration in selectivity).

Absorbance change and static quenching of fluorescence of meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) by trinitrotoluene (TNT)

Meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) interacts with trinitrotoluene (TNT) and forms a 1:1 complex with a new absorbance peak at 422 nm. TNT quenches TPPS emission intensity at 645 and 702 nm when excited at 413 nm. The TPPS-TNT complex is formed in the ground state on the basis of a linear Stern-Volmer plot indicative of static quenching. The association constants determined from absorbance and fluorescence studies are in excellent agreement.

Electrochemical High-Content Screening of Nitric Oxide Release from Endothelial Cells

Release of nitric oxide (NO) is of high importance for regulating endothelial cell functions during vasodilatation, vascular remodeling, and angiogenesis. Thus, a direct and reliable real-time method for NO detection that takes into account time-dependent variations of the NO concentration in the complex reaction within the diffusion zone above the cells is vital for obtaining information about the role of NO in intracellular endothelial signal transduction and its impact on the surrounding cells. In this study, the time course of vascular endothelial growth factor E (VEGF-E) stimulated NO release from transformed human umbilical vein endothelial cells (T-HUVEC) was investigated by means of metalloporphyrin-based NO sensors employed in an electrochemical robotic system. The NO sensor was obtained by electrochemically induced deposition of Ni(II) tetrakis(p-nitrophenylporphyrin) on a 50-microm diameter platinum disk electrode which was integrated, together with a 25-microm diameter platinum disk, in a double-barrel electrode arrangement. The second electrode was used as a guidance sensor for the automatic and highly reproducible positioning of the NO sensor at a known distance from a layer of adherently growing cells by using z-approach curves in the negative feedback mode of scanning electrochemical microscopy (SECM). The electrochemical robotic system allows the fully automated detection of NO with high sensitivity and selectivity to be performed in real time within 96-well microtiter plates. A functional cell assay was established to allow the standardized detection of NO released upon stimulation from T-HUVEC with a sensor positioned at a known distance above the endothelial cells. The overall system was evaluated by automatic detection of NO release from T-HUVEC upon stimulation with VEGF-E after incubation with a variety of drugs that are known to act on different sites in the complex signal-transduction pathway that finally invokes NO release.