A dual electrochemical sensor for nitrite and nitric oxide

Nafion/lead-ruthenate pyrochlore chemically modified electrode (NPyCME) showed a remarkable dual sensing activity toward NO2- oxidation and NO reduction as demonstrated by cyclic voltammetry (CV), ac-impedance spectroscopy and flow injection analysis (FIA). The mechanistic parameters of current function, charge transfer resistance and exchange current for the NPyCME, GCE and Nafion-coated GCE were evaluated and compared. The disproportionation reaction of NIIIO2- into NIVO3- + NIIO in acidic solution was used as a model system for testing the dual sensing ability of the NPyCME. The obtained crossover peak response for NO2- oxidation and NO reduction in pH 1.65 buffer solution gave the direct proof for the applicability of the NPyCME in the dual electrocatalytic action. By flow injection analysis, under optimized conditions, the calibration curve was linear in the range of 100 nM-100 microM and 800 nM-63.3 microM and the detection limit (S/N = 3) was 4.8 nM and 15.6 nM for NO2- and NO, respectively.     

Dirhodium tetracarboxylate scaffolds as reversible fluorescence-based nitric oxide sensors

We report the synthesis and characterization of dirhodium tetracarboxylate complexes [Rh(2)(mu-O(2)CR)(4)(L)(2)], with R = Me and L = dansyl-imidazole (Ds-im) or dansyl-piperazine (Ds-pip). The fluorophores coordinate to the axial sites of the dirhodium core through the imidazole or piperazine N-atom and emit only weakly when excited at 365 or 345 nm for the Ds-im and Ds-pip complexes, respectively. These fluorophore-containing complexes were investigated for their ability to elicit a fluorescence response in the presence of NO. An immediate increase in fluorescence emission of greater than 15-fold occurs when NO is admitted to solutions containing [Rh(2)(mu-O(2)CMe)(4)] and Ds-pip or Ds-im. In both systems, the fluorescence response, which arises by NO-induced displacement of the axially coordinated fluorophore, is reversible with a sensitivity of approximately 4 microM. The related dinitrosyl complexes [Rh(2)(mu-O(2)CR)(4)(NO)(2)], where R = Me, Et, or n-Pr, were prepared, structurally characterized, and found to be air-stable, losing NO upon standing in solution. Sequestration of a methylene chloride solution of the Ds-pip complex from aqueous media by a NO-permeable membrane allows for fluorescence detection of NO for potential applications in biological fluids.     

Conjugated polymer-based fluorescence turn-on sensor for nitric oxide

A turn-on fluorescent sensor for NO (g) in solution was synthesized using a bipyridyl-substituted poly(p-phenylene vinylene) derivative (CP1) as the sensory scaffold. The action of NO (g) upon the CP1-Cu(II) complex reduces it to the CP1-Cu(I) complex with a concomitant 2.8-fold increase in emission intensity. The reagent is selective for NO (g) versus other biological reactive nitrogen species, except for nitroxyl, and has a detection sensitivity limit of 6.3 nM. [structure: see text]     

Development and application of a nano-alumina based nitric oxide sensor

Microchimica Acta - A novel sensor is described for the sensitive determination of nitric oxide (NO) based on a nano-alumina (nano-Al2O3) modified glassy carbon electrode. Cyclic voltammetry,...     

Mechanistic studies on the reversible binding of nitric oxide to metmyoglobin.

The ferriheme protein metmyoglobin (metMb) in buffer solution at physiological pH 7.4 reversibly binds the biomessenger molecule nitric oxide to yield the nitrosyl adduct (metMb(NO)). The kinetics of the association and dissociation processes were investigated by both laser flash photolysis and stopped-flow kinetics techniques at ambient and high pressure, in three laboratories using several different sources of metMb. The activation parameters DeltaH, DeltaS, and DeltaV were calculated from the kinetic effects of varying temperature and hydrostatic pressure. For the "on" reaction of metMb plus NO, reasonable agreement was found between the various techniques with DeltaH(on), DeltaS(on), and DeltaV(on) determined to have the respective values approximately 65 kJ mol(-1), approximately 60 J mol(-1) K(-1), and approximately 20 cm(3) mol(-1). The large and positive DeltaS and DeltaV values are consistent with the operation of a limiting dissociative ligand substitution mechanism whereby dissociation of the H(2)O occupying the sixth distal coordination site of metMb must precede formation of the Fe-NO bond. While the activation enthalpies of the "off" reaction displayed reasonable agreement between the various techniques (ranging from 68 to 83 kJ mol(-1)), poorer agreement was found for the DeltaS(off) values. For this reason, the kinetics for the "off" reaction were determined more directly via NO trapping experiments, which gave the respective activation parameters DeltaH(off) = 76 kJ mol(-1), DeltaS(off) = approximately 41 J mol(-1) K(-1), and DeltaV(off) = 20 cm(3) mol(-1)), again consistent with a limiting dissociative mechanism. These results are discussed in reference to other investigations of the reactions of NO with both model systems and metalloproteins.     

Visible light induced reversible extrusion of nitric oxide from a ruthenium(II) nitrosyl complex: a facile delivery of nitric oxide

The new ruthenium compound [Ru(NO)(pysiS4)]Br (3) (pysiS4 = 2,6-bis(3-triphenylsilyl-2-sulfanylphenylthiomethyl)pyridine), containing sterically bulky SiPh3 groups ortho to the thiolate donors, has been synthesized. In solution, 3 releases NO efficiently on exposure to visible light (lambda >/= 455 nm) at room temperature to afford [Ru(Br)(pysiS4)] (4). Treatment of 4 with NO yielded exclusively 3 without any metal-bound side reaction.     

A novel electrochemical sensor based on nano-structured film electrode for monitoring nitric oxide in living tissues

A sensor exhibited high sensitivity and good selectivity for determination of nitric oxide (NO) was fabricated. The sensor was constructured by coating Nafion/multi-walled carbon nanoubes-chitosan-gold nanoparticles (Nafion/MWNTs-CS-AuNPs) film on glassy carbon electrode (GCE). Several key parameters affecting on the electrochemical response were optimized, such as the film thickness, applied potential and volume of Nafion. The sensor showed good linear relationship with the NO concentration in the range of 1.90 × 10⁻⁸ to 5.40 × 10⁻⁵ M and with the detection limit of 7.60 × 10⁻⁹ M (S/N = 3). Finally, the sensor was successfully applied to the monitoring of NO release from living tissues, including mouse kidney, heart, spleen and liver (a slice). NO release at micro-molar level can be detected while the NO donor l-arginine (l-Arg), nitroglycerin (GTN) and aspirin (ASA) was present. It was interestedly found that the capacities to induce NO generation were in the order of GTN > ASA > l-Arg when these stimulants were converted to the same concentration. In addition, the NO release is associated with the functional groups in these donors.     

A turn-on and reversible fluorescence sensor for zinc ion

A simple Schiff base type fluorescent receptor was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor exhibits an "off-on-type" mode with high selectivity in the presence of Zn(2+) ion. The addition of EDTA quenches the fluorescence of receptor -Zn(2+) complex, making receptor a reversible chemosensor. The selectivity of for Zn(2+) is the consequence of combined effects of CHEF, C[double bond, length as m-dash]N isomerization and inhibition of ESIPT.     

On-chip multi-electrochemical sensor array platform for simultaneous screening of nitric oxide and peroxynitrite

In this work we report on the design, microfabrication and analytical performances of a new electrochemical sensor array (ESA) which allows for the first time the simultaneous amperometric detection of nitric oxide (NO) and peroxynitrite (ONOO(-)), two biologically relevant molecules. The on-chip device includes individually addressable sets of gold ultramicroelectrodes (UMEs) of 50 μm diameter, Ag/AgCl reference electrode and gold counter electrode. The electrodes are separated into two groups; each has one reference electrode, one counter electrode and 110 UMEs specifically tailored to detect a specific analyte. The ESA is incorporated on a custom interface with a cell culture well and spring contact pins that can be easily interconnected to an external multichannel potentiostat. Each UME of the network dedicated to the detection of NO is electrochemically modified by electrodepositing thin layers of poly(eugenol) and poly(phenol). The detection of NO is performed amperometrically at 0.8 V vs. Ag/AgCl in phosphate buffer solution (PBS, pH = 7.4) and other buffers adapted to biological cell culture, using a NO-donor. The network of UMEs dedicated to the detection of ONOO(-) is used without further chemical modification of the surface and the uncoated gold electrodes operate at -0.1 V vs. Ag/AgCl to detect the reduction of ONOOH in PBS. The selectivity issue of both sensors against major biologically relevant interfering analytes is examined. Simultaneous detection of NO and ONOO(-) in PBS is also achieved.     

A thionine-based reversible redox sensor in a sequential injection system

According to the current demands of Green Analytical Chemistry and regarding the need for lower reagent consumption with improved analytical performance, an automatic methodology with a flow-through optosensor incorporating solid-phase spectrophotometric detection was developed. The sensor used in this work was based on the redox state of thionine whose oxidized form is blue and reduced form is colorless with monitoring carried out at 621 nm. This redox indicator was immobilized on gel beads and subsequently packed into a flow-through cell. It was then assembled into a sequential injection system and was shown to be an excellent alternative to monitor enzymatic redox reactions automatically as the redox catalysis is performed by glucose dehydrogenase. This enzyme is a representative dehydrogenase enzyme and uses NAD⁺ as cofactor, promoting the oxidation of glucose to glucono-lactone and reduction of NAD⁺ to NADH. The produced NADH promotes color depletion on the surface of the sensor. The calibration graph for glucose was linear between 5.74 × 10⁻⁴ and 2.00 × 10⁻³ mol L⁻¹ and detection limit was 1.72 × 10⁻⁴ mol L⁻¹. Glucose concentration in different samples including sera, salines, perfusion solutions, powder for preparing oral solutions and solutions for hemodialysis was determined. The method proved to be reproducible with a RSD < 5% for glucose determinations.     

Magnesium oxide nanocubes deposited on an overhead projector sheet: synthesis and resistivity-based hydrogen sensing capability

Microchimica Acta - This work reports the growth of magnesium oxide (MgO) nanocubes by thermal chemical vapor deposition at various temperatures. The MgO nanocubes were investigated by X-ray...     

A novel oxygen-dependent deoximation by nitric oxide

A variety of aldoximes and ketoximes were oxidized to corresponding aldehydes and ketones by nitric oxide in the presence of oxygen.A presumed mechanism was suggested.     

A novel amperometric sensor for the determination of nitric oxide, and its application in rat liver cells

A novel amperometric nitric oxide sensor with a wide linear range, low detection limit and fast response time was developed. The sensor was fabricated using a poly-brilliant cresyl blue (PBCB)/Nafion film modified glassy carbon electrode (GCE). The PBCB on the working GCE surface dramatically improves the oxidation response of nitric oxide and lowers the required potential for the two-step oxidation of NO. Otherwise, Nafion coated onto the film electrode surface does not only improve the selectivity of the sensor, but also further lowers the active energy of the direct three-electron oxidation of NO to nitrate. The effect of the preanodic time and the film thickness of the electropolymerization on the nitric oxide response as well as the volume of Nafion coated onto the surface and the potential for amperometric detection were optimized. This novel sensor has been applied to the determination of NO released from rat liver cells, and the result is satisfactory. Correspondence: Sheng Shui Hu, Department of Chemistry, Wuhan University, Wuhan 430072, P.R. China     

Noncovalently functionalized water-soluble multiwall-nanotubes through azocarmine B and their application in nitric oxide sensor

A new noncovalent approach for the dissolution of MWNTs in water by azocarmine B (ACB) is reported. Through a simple electro-polymerization procedure, a novel electrochemical NO sensor based on water-soluble MWNTs and polyazocarmine B (PACB) nanofilm electrode was prepared, which showed excellent electrocatalytic activity towards the oxidation of nitric oxide (NO). The oxidation current linearly increased with the nitric oxide concentration in the range of 2.2 × 10⁻⁷–1.2 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.8 × 10⁻⁸ mol L⁻¹. The sensor has the merit of good stability, reproducibility, high sensitivity and selectivity, and it can be used to monitor NO released from rat liver cells effectively.     

Bifunctional sensor of nitric oxide and oxygen based on hematite nanotubes embedded in chitosan matrix

A novel hybrid bifunctional sensing platform for simultaneous determination of NO and O₂ has been developed, whereby hematite nanotubes are immobilized into the chitosan matrix onto a gold electrode (labeled as HeNTs-Chi/Au). The HeNTs distributed in porous-structured chitosan matrix not only offer abundant active sites for bifunctional sensing of NO and O₂, but also facilitate oxidation of NO and reduction of O₂ dramatically. Straight calibration curves are achieved in analyte concentration ranges of 5.0 × 10⁻⁸ to 1.25 × 10⁻⁶ mol L⁻¹ for NO and 2.5 × 10⁻⁷ to 6.0 × 10⁻⁶ mol L⁻¹ for O₂. Also, the detection limits are low of 8.0 × 10⁻⁹ mol L⁻¹ for NO and 5.0 × 10⁻⁸ mol L⁻¹ for O₂. Such an efficient bifunctional sensor for NO and O₂ offers great potential in quantitation of NO levels in biological and medical systems, since NO level is highly regulated by various reactive oxygen species.     

Protein thiyl free radicals produced by nitric oxide and nitric oxide donors

The spin-trapping technique was used to study the radical intermediates produced by reaction of nitric oxide (^*NO) and peroxynitrite with serum albumin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Our results show that the major radical product induced by ^*NO and by peroxynitrite with serum albumin and GAPDH was a thiyl radical. The same radical can be detected in the ^*NO-transfer from S-nitroso albumin to low molecular weight thiols. Moreover, ^*NO or peroxynitrite treatment of GAPDH was able to induce NAD-dependent covalent modification of the enzyme in erythrocyte ghosts.