Determination Of Nitric Oxide Concentrations Research Articles

Single-Walled Carbon Nanotube-Based Biosensors for Detection of Bronchial Inflammation

Inflammation is a protective mechanism against invading pathogens and tissue damage. However, the inflammatory process is implicated in a wide range of diseases affecting all organs and body systems. Nitric oxide — a multifunctional signaling molecule that plays a critical role in systemic blood pressure homeostasis, prevention of platelet aggregation, antimicrobial resistance, immunoregulation, tumor suppression and as a neurotransmitter — is used as a surrogate marker for inflammation. However, the most commonly used Griess assay is an indirect and expensive method for the determination of nitric oxide concentration. Hence, single-walled carbon nanotube-based biosensors have been explored as real-time, sensitive, selective and safe methods to determine nitric oxide released during the inflammatory process. In this review, we explore current developments in single-walled carbon nanotube-based biosensors for the detection of nitric oxide in exhaled breath as a direct and noninvasive test for detection of bronchial inflammation.

Reactions of nitrite in erythrocyte suspensions measured by membrane inlet mass spectrometry

The reactions of nitrite with deoxygenated human erythrocytes were examined using membrane inlet mass spectrometry to detect the accumulation of NO in an extracellular solution. In this method an inlet utilizing a silicon rubber membrane is submerged in cell suspensions and allows NO to pass from the extracellular solution into the mass spectrometer. This provides a direct, continuous, and quantitative determination of nitric oxide concentrations over long periods without the necessity of purging the suspension with inert gas. We have not observed accumulation of NO compared with controls on a physiologically relevant time scale and conclude that, within the limitations of the mass spectrometric method and our experimental conditions, erythrocytes do not generate a net efflux of NO after the addition of millimolar concentrations of nitrite. Moreover, there was no evidence at the mass spectrometer of the accumulation of a peak at mass 76 that would indicate N 2O 3, an intermediate that decays into NO and NO 2. Inhibition of red cell membrane anion exchangers and aquaporins did not affect these processes.

Direct Measurement of Nitric Oxide in Seawater Medium by Fluorometric Method

The determination of nitric oxide (NO) concentration in seawater medium by fluorometric method has been investigated, based on the reaction that 2,3-diaminonaphthalene (DAN) has the ability to trap NO to yield the highly fluorescent 2,3-naphthotriazole (NAT). The optimum conditions, such as fluorometric determination conditions (λex = 383 nm, λem = 410 nm), the influence of temperature and equilibrium time on the DAN trapping NO, and the influence of DAN solution on trapping NO, have been examined. The fluorometric intensity is linear with the NO concentration in the range of 1.4–1400 nM with a R2 of 0.9985 (P < 0.0001). The limit of detection is 1 nM (S/N = 3), the relative standard deviation is 1.63% (NO, 14 nM), and there is no interference from the medium. Compared with fluorescence determination of NO concentration in NaOH medium, this method decreases the limit of detection by one order of magnitude. Combining the purge-and-trap operation, the NO concentration of seawater in Shilaoren of Qingdao (36°05′46″N; 120°29′40″E) was detected to be (0.12 ± 0.01) nM. The method can also be applied to monitor the self-releasing NO change of sodium nitroprusside in seawater.

Serum nitrate and nitrite in dogs with spontaneous cardiac disease.

The purpose of this study was to determine whether nitric oxide (NO) concentrations are high in dogs with chronic valvular disease (CVD) and dilated cardiomyopathy (DCM) compared to healthy controls and to determine whether NO concentrations are correlated with type of cardiac disease, disease severity, medical therapy, or serum tumor necrosis factor (TNF) and interleukin-1 (IL-1). Blood was collected from 32 dogs with DCM, from 10 dogs with CVD, and from 10 healthy controls. Indirect determination of NO concentrations was performed by a commercial photoabsorbance assay that uses a Greiss reagent to measure the concentration of nitrite and nitrate (NN), end products of NO metabolism. TNF and IL-1 activities were measured by bioassay. Mean NN concentrations were significantly higher in dogs with heart disease (median, 4.57 microM; range, 0.00-31.05 microM) than in controls (median, 0.00 microM; range, 0.00-6.16 microM; P = .04). NN concentrations in dogs with cardiac disease were not correlated with type or severity of cardiac disease, medication type, or TNF and IL-1 concentrations. NN concentrations were inversely correlated with fractional shortening. The results of this study suggest that metabolites of NO are increased in some dogs with cardiac disease, but these increases appear to be independent of disease severity, TNF and IL-1 concentrations, and type of pharmacologic intervention.

A new optical sensing reaction for nitric oxide

Based on the reaction between the Cu(II) complex of Eriochrome cyanine R (ECR) and nitric oxide (NO) in phosphate buffer (pH 7.4), a new colorimetric method for the determination of NO concentration has been developed. The linear calibration range for NO was 0–60 μM with a detection limit of 1.24 μM. This reaction was then used as the basis in the development of a fibre optic chemical sensor for NO gas. The copper complex was incorporated into silicone rubber membranes and exposed to NO gas after incubating the films in phosphate buffer (pH 7.4). A linear calibration for NO gas between 0 and 6 ppm was obtained with a detection limit of 0.227 ppm (1 μM ≃ 0.031 ppm NO in solution). The sensor response was shown to be reproducible and reversible (2.77%, R.S.D., n=4) upon exposure to aqueous phosphate buffer (pH 7.4). The sensor response was also found to be pH independent between 7 and 10.

Application of the electrocatalytic reduction of nitric oxide mediated by ferrioxamine B to the determination of nitric oxide concentrations in solution

The electrocatalytic reduction of nitric oxide to nitrous oxide by the iron siderophore ferrioxamine B was used as a basis for an electrochemical NO sensor. Evaporation of a Nafion film onto a glassy carbon electrode produced modified surfaces into which the ferric complex of ferrioxamine B could be exchanged. Cyclic voltammetry of this modified electrode in aqueous solution produced two peaks, one of which (−0.73 V versus SSCE) corresponded to the quasi-reversible reduction of solution-bound ferrioxamine B and the other of which (−0.42 V) corresponded to an adsorbed species. Greater catalytic enhancement was observed in the presence of NO for the solution wave than for the adsorption pre-peak. The catalytic enhancement, expressed as the ratio of peak current in the presence of NO ( i cat) to the current in the absence of NO ( i d) was a linear function of the solution NO concentration down to 1 μM. Better sensitivity was precluded by decomposition of the reduced form of the catalyst in the absence of NO.

Colorimetric Methods for the Determination of Nitric Oxide Concentration in Neutral Aqueous Solutions

Two convenient colorimetric methods are described for the determination of nitric oxide (NO) concentration in neutral aqueous solutions. Both techniques take advantage of the fact that nitrosating and oxidizing intermediates are generated in the course of the NO/O2 reaction. In the first method, 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) is oxidized to the corresponding cation radical, imparting to the solution an intense green color (λmax = 420 nm). The second method involves the nitrosation of suifanilamide in the presence of N-(1-naphthyl)ethylenediamine dihydrochloride, yielding an azo dye which imparts an intense orange color (λmax = 496 nm) to the solution. The presence of nitrite at concentrations <10 mM does not interfere with either assay. The dramatic UV–visible absorbance changes that occur during the course of these reactions provide a clear visual indication of the presence of NO in test solutions.

Determination of nitric oxide concentrations from sunrise E‐region electron density measurements

Midlatitude sunrise electron density profiles have been analyzed in order to determine nitric oxide concentrations in the range 100–160 km. In general, the determinations are restricted to heights for which the ionization of nitric oxide by direct solar Lyman‐α radiation is the main contribution to the growth of the E region. The concentrations obtained are larger, by factors of approximately 3 to 4, than those obtained from the midlatitude airglow measurements of other workers. Concentrations have been obtained from one sunset measurement and these are significantly lower than the sunrise values. The results also give a clear indication of increasing nitric oxide concentrations above 120 km with increasing solar activity.

Determination of nitric oxide concentrations from eclipse variations of ion concentrations

It is shown how nitric oxide concentrations in the upper atmosphere may be derived from the observation of changes in the [NO +] [O 2 +] concentration ratio and electron concentration and temperature. Experimental data obtained during the 1970 eclipse at Wallops Island are analyzed to give nitric oxide concentration profiles above 130 km. A value of 2 × 10 7 cm -3is obtained for the concentration at 130 km.

Rapid Continuous Determination of Nitric Oxide Concentration in Exhaust Gases

The rapid determination of nitric oxide levels in exhaust gases is required both for laboratory studies of the exhaust emission characteristics of combustion engines and for routine inspection of motor vehicle exhaust. A continuous sampling, continuous analysis method for measuring nitric oxide has been demonstrated. Rapid oxidation of nitric oxide to nitrogen dioxide is obtained through ozonization. Nitrogen dioxide concentrations are determined by means of an ultraviolet absorption technique. Nitric oxide concentrations between 100 and 5000 ppm have been measured and response time of about 20 seconds obtained. The presence of unburned hydrocarbons in the exhaust sample has an adverse effect on the results of this technique which requires either the removal of hydrocarbons or adjustment of ozone concentration.