Nitric Oxide Gas Sensor Research Articles

Flexible NO gas sensor based on conducting polymer poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT)

Flexible gas sensor for Nitric Oxide (NO) detection has been realized using conducting polymer poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) as the gas sensing material. This has been achieved by the deposition of PCDTBT on flexible BOPET substrate using the simple technique of spin coating. PCDTBT has been found to be highly selective for NO gas with a very good response for upto 5ppm level of NO gas (toxic limit - 25ppm). The XPS study on PCDTBT films has revealed no change in the chemical composition of deposited PCDTBT polymer, thus, showing no degradation of deposited film by the oxygen or moisture present in the ambient atmosphere during the gas sensing measurements. The gas sensing measurements were done for 35days to determine the reproducibility of sensor. The measurements confirmed the long term environmental stability of PCDTBT showing it to be a reliable and effective material for NO gas sensor. In addition, the gas sensing measurements of PCDTBT under bending conditions with improved performance were also carried out, showing its application as a novel gas sensing material for the flexible NO gas sensor. The possible gas sensing mechanism of PCDTBT, a p-type material, was also investigated using work function and impedance spectroscopy measurements.

Effect of Electrode Configuration on Nitric Oxide Gas Sensor Behavior.

The influence of electrode configuration on the impedancemetric response of nitric oxide (NO) gas sensors was investigated for solid electrochemical cells [Au/yttria-stabilized zirconia (YSZ)/Au)]. Fabrication of the sensors was carried out at 1050 °C in order to establish a porous YSZ electrolyte that enabled gas diffusion. Two electrode configurations were studied where Au wire electrodes were either embedded within or wrapped around the YSZ electrolyte. The electrical response of the sensors was collected via impedance spectroscopy under various operating conditions where gas concentrations ranged from 0 to 100 ppm NO and 1%–18% O2 at temperatures varying from 600 to 700 °C. Gas diffusion appeared to be a rate-limiting mechanism in sensors where the electrode configuration resulted in longer diffusion pathways. The temperature dependence of the NO sensors studied was independent of the electrode configuration. Analysis of the impedance data, along with equivalent circuit modeling indicated the electrode configuration of the sensor effected gas and ionic transport pathways, capacitance behavior, and NO sensitivity.

A room temperature nitric oxide gas sensor based on a copper-ion-doped polyaniline/tungsten oxide nanocomposite.

The parts-per-billion-level nitric oxide (NO) gas sensing capability of a copper-ion-doped polyaniline/tungsten oxide nanocomposite (Cu2+/PANI/WO3) film coated on a Rayleigh surface acoustic wave device was investigated. The sensor developed in this study was sensitive to NO gas at room temperature in dry nitrogen. The surface morphology, dopant distribution, and electric properties were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy mapping, and Hall effect measurements, respectively. The Cu2+/PANI/WO3 film exhibited high NO gas sensitivity and selectivity as well as long-term stability. At 1 ppb of NO, a signal with a frequency shift of 4.3 ppm and a signal-to-noise ratio of 17 was observed. The sensor exhibited distinct selectivity toward NO gas with no substantial response to O2, NH3 and CO2 gases.

Disposable Screen-Printed Edge Band Ultramicroelectrodes for Use as Nitric Oxide Gas Sensor in Designing an Easily Applicable Method for Real Sample Analysis of Nitrite with Superior Selectivity and Sensitivity

We report here an easily applicable method for the quantification of nitrite (NO2−) in real samples. This approach simplified the two steps of sample preparation and detection into a 2-in-1 single step process. Samples were digested in sulfuric acid and the as-generated nitric oxide (NO) was detected by an electrochemical sensor in the gas phase. It eliminated almost all of the interferents in the solution phase and hence resulted in a highly selective determination of nitrite suitable for food samples with complicated matrix. We successfully demonstrated the determination of nitrite in sausage and vegetables and further validated the results with an AOAC official reference method.

Fabrication of a nitric oxide gas sensor using microwires and basic research for its application

Purpose: Although nitric oxide (NO) is considered one of the initial signals that promote postsurgery liver regeneration, NO’s exact role in the liver regeneration mechanism is still not clear. Therefore, developing a practical gas sensor and testing it in a clinical setting through basic research will lay the groundwork for advanced clinical research on the action mechanism of NO. Methods: A thin nano wire NO sensor was made by wrapping a pair of parlyene-coated gold wires around a needle. The NO blood concentration determined by measuring the potential difference across the oscilloscope using electrical conductivity. In order to measure changes in NO level before and after the surgery, the NO sensor was inserted in the hepatic portal vein and a 75 percent partial hepatectomy was performed. The NO blood concentration was measured regularly with both the NO kit and the sensor. Results: One significant challenge was separation of the wire upon insertion into the hepatic portal vein. Despite separation, the constant measurements of the wire-type sensor were similar to those measured by the NO measurement kit. Conclusion: The development of a needle-type sensor allowed for easier insertion. In the future, using difference in electric potential, as used in the NO sensor, may be a more effective method of measuring blood ion concentration.

Amperometric Nitric Oxide Sensors with Enhanced Selectivity Over Carbon Monoxide via Platinum Oxide Formation Under Alkaline Conditions

An improved planar amperometric nitric oxide (NO) sensor with enhanced selectivity over carbon monoxide (CO), which represents a volatile interfering species for NO sensors that has been largely overlooked until recently, is described. Formation of an oxide film on the inner platinum working electrode via anodic polarization using an inner alkaline electrolyte solution provides the basis for improved selectivity. Cyclic voltammetry reveals that formation of an oxidized Pt film inhibits adsorption of CO to the electrode surface, which is a necessary initial step in the electrocatalytic oxidation of CO on Pt. Previous NO gas sensors that employ internal electrolyte solutions have been assembled using acidic internal solutions that inhibit the formation of a dense platinum oxide film on the working electrode surface. It is demonstrated herein that increasing the internal electrolyte pH promotes oxidized platinum film formation, resulting in improved selectivity over CO. Selectivity coefficients (log KNO,j) for sensors assembled with internal solutions at various pH values range from -0.08 at pH 2.0 to -2.06 at pH 11.7, with average NO sensitivities of 1.24 nA/μM and a limit of detection (LOD) of <1 nM.

A nitric oxide gas sensor based on Rayleigh surface acoustic wave resonator for room temperature operation

A Rayleigh surface acoustic wave (RSAW) resonator with polyaniline/tungsten oxide nanocomposite thin film is investigated as a gas sensor for detecting the presence of nitric oxide (NO) in air. The sensor developed in this work was sensitive to NO gas at room temperature. It is shown that the sensor had a frequency shift of 1.2 ppm when it was exposed to 138 ppb NO. The negative frequency response increased with NO concentration increasing. The response and recovery times of the NO sensor in this work were about 20–80 s. In addition, this RSAW sensor also exhibited reversibility and repeatability to the presence of NO gas. Especially, the presented sensor showed high selectivity with NO gas to separate from NO 2 and CO 2 gases.

Modeling the Effect of Oxygen on the Amperometric Response of Immobilized Organoselenium-Based S-Nitrosothiol Sensors

Amperometric detection of S-nitrosothiols (RSNOs) at submicromolar levels in blood samples is of potential importance for monitoring endothelial function and other disease states that involve changes in physiological nitric oxide (NO) production. It is shown here that the elimination of dissolved oxygen from samples is critical when covalently attached diselenocystamine-based amperometric RSNO sensors are used for practical RSNO measurements. The newest generation of RSNO sensors utilizes an amperometric NO gas sensor with a thin organoselenium modified dialysis membrane mounted at the distal sensing tip. Sample RSNOs are catalytically reduced to NO within the dialysis membrane by the immobilized organoselenium species. In the presence of oxygen, the sensitivity of these sensors for measuring low levels of RSNOs (<μM) is greatly reduced. It is demonstrated that the main scavenger of the generated nitric oxide is not the dissolved oxygen but rather superoxide anion radical generated from the reaction of the reduced organoselenium species (the reactive species in the catalytic redox cycle) and dissolved oxygen. Computer simulations of the response of the RSNO sensor using rate constants and diffusion coefficients for the reactions involved, known from the literature or estimated from fitting to the observed amperometric response curves, as well as the specific geometric dimensions of the RSNO sensor, further support that nitric oxide and superoxide anion radical quickly react resulting in near zero sensor sensitivity toward RSNO concentrations in the submicromolar concentration range. Elimination of oxygen from samples helps improve sensor detection limits to ca. 10 nM levels of RSNOs.

Using a PEDOT:PSS modified electrode for detecting nitric oxide gas

PEDOT:PSS thick films, prepared by the drop-coated method, were used in this study for sensing nitric oxide (NO) gas. The thickness of PEDOT-PSS film was controlled by dropping different volumes of PEDOT-PSS solution to improve the response of PEDOT-PSS film. Due to its porous structure, the thicker the PEDOT-PSS film is, the higher the noticeable surface area. Thus, a larger response is found. However, since the concentration of NO gas used was low (10 ppm), the effect of the surface area was not noticeable when the thickness of the film was greater than 5 μm. In the range of 2.5–10 ppm NO, the relationship between the response of the PEDOT-PSS film and the NO concentration was linear. The limit of detection ( S/ N = 3), response time ( t 95), and recovery time ( t 95) were about 350 ppb, 527 s, and 1780 s, respectively. The response of PEDOT-PSS film to 10 ppm NO gas was dramatically affected by the presence of either O 2 or CO. The standard deviation, with respect to the sensitivity of the NO gas sensor based on PEDOT:PSS film, was 2.2%. The sensitivity of the sensor remained at about 74.5% that of a fresh one.

Nitric oxide gas sensors with functionalized carbon nanotubes

AbstractNitric oxide (NO) gas sensing with carboxyl functionalized single‐ and multi‐walled carbon nanotubes (SWCNTs and MWCNTs) is demonstrated in this work. Stable solutions of the carboxylated nanotubes were made and then drop‐cast on alumina substrates equipped with gold electrodes and also with platinum heater elements. The obtained resistive nanotube sensors were tested in a 2‐point setup at different temperatures and NO gas concentrations up to 100 ppm in synthetic air and also in argon buffer. When exposed to NO, the conductivity of the sensors changed up to ∼40% for SWCNTs and ∼12% for MWCNTs; however, in the investigated regime, the response was found to be fairly independent on NO concentration. Though all sensors showed practically instantaneous gas response, the time needed for saturation (few tens of minutes) was found to be concentration dependent. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Direct Detection of S-Nitrosothiols Using Planar Amperometric Nitric Oxide Sensor Modified with Polymeric Films Containing Catalytic Copper Species

The direct amperometric detection of S-nitrosothiol species (RSNOs) is realized by modifying a previously reported amperometric nitric oxide gas sensor with thin hydrophilic polyurethane films containing catalytic Cu(II)/(I) sites. Catalytic Cu(II)/(I)-mediated decomposition of S-nitrosothiols generates NO(g) in the thin polymeric film at the distal tip of the NO sensor. Three different species are examined to create the catalytic layer: (1) a lipophilic Cu(II)-ligand complex; (2) Cu(II)-phosphate salt; and (3) small (3-microm) metallic Cu(0) particles. All three catalytic layers yield reversible amperometric response in proportion to the concentration of S-nitrosothiols (e.g., nitrosocysteine, nitrosoglutathione, S-nitroso-N-acetylcysteine, S-nitrosoalbumin) present in the aqueous test solution. Sensitivity toward the different RSNO species is dependent on the respective catalytic rates of decomposition of the RSNO species by reactive Cu(I), accessibility of the species into the polyurethane layer containing the catalyst, the level of reducing agents (ascorbate) used in solution to help generate reactive Cu(I) species, and the concentration of metal ion complexing agents present in the test solution (e.g., EDTA). Under optimized conditions, all RSNO species can be detected at < or =1 microM levels, with sensor lifetimes of at least 10 days for the sensors based on Cu(II)-phosphate and Cu0 particles. It is further shown that the new RSNO sensors can be used to assess the "NO-generating" ability of fresh blood samples by effectively detecting the total level of reactive RSNO species present in such samples.

A kinetic study for electrooxidation of NO gas at a Pt/membrane electrode-application to amperometric NO sensor

The electrochemical oxidation of nitric oxide (NO) gas at a Pt/membrane electrode has been studied. The Pt/Nafion ® electrode was prepared by the impregnation–reduction (I–R) chemical plating method and was tested over the NO concentration range from 0 to 500 ppm. It is assumed that the electrooxidation of NO gas at the electrode can be considered as an irreversible process, from which a transcendental equation describing the I– E relationship can be derived. The derived I– E relationship fits the experimental data reasonably well. Several electrochemical parameters for the reaction, including the half-wave potential ( E 1/2), the standard apparent rate constant ( rak 0), the transfer coefficient ( α), and the exchange current density ( i 0) can be extracted from the experimental data. Under the kinetic controlled regime, with the potential in the range of 0.7–0.9 V (versus Ag/AgCl/sat. KCl), the kinetic model predicts the electrooxidative behavior of NO at a Pt/Nafion ® electrode over a wide concentration range of 100–500 ppm. An amperometric NO gas sensor based on a Pt/Nafion ® electrode has been fabricated and tested over the NO concentration range from 0 to 500 ppm at 1.15 V (versus Ag/AgCl/sat. KCl) and a flow rate of 200 ml per min.

A New Nitric Oxide Gas Sensor Based on Reticulated Vitreous Carbon/Nafion and Its Applications

AbstractReticulated vitreous carbon (RVC), and Nafion membrane are used to fabricate a composition electrode to measure nitric oxide (NO) concentration amperometrically in the gas phase. Limit of detection was found to be 6 ppb at an applied voltage of 0.66 V (vs. mercury sulfate reference electrode) with average response time of less than 30 seconds. The response of the sensor was linearly dependent on the concentration over the whole tested range from 19 ppb‐50 ppm of NO. Simplicity in electrode fabrication and consistent performance between individual sensors make RVC and Nafion attractive materials for detecting very low levels of nitric oxide gas in routine analysis.

On the Electrooxidation and Amperometric Detection of NO Gas at the Pt/Nafion® Electrode

The electrochemical oxidation of nitric oxide (NO) gas at the Pt/Nafion® electrode has been studied at a concentration of 500 ppm. The electrooxidation of NO taking place over a wide potential range can be described by a transcendental equation, from which the half-wave potential of the reaction can be determined. For NO oxidation with appreciable overpotentials but negligible mass-transfer effects, the Tafel kinetics applies. The obtained charge transfer coefficient (a) and the exchange current density (io) are 0.77 and 14 mA/cm2, respectively. An amperometric NO gas sensor based on the Pt/Nafion® electrode has been fabricated and tested over the NO concentration range from 0 to 500 ppm. The Pt/Nafion® electrode was used as an anode at a fixed potential, preferably 1.15 V (vs. Ag/AgCl/sat. KCl), which assures current limitation by diffusion only. The sensitivity of the electrochemical sensor was found to be 1.86 mA/ppm/cm2. The potential interference by other gases, such as nitrogen dioxide (NO2) and carbon monoxide (CO), was also studied in the range 0-500 ppm. Both sensitivity for NO and selectivity of NO over NO2/CO show significant enhancement upon using a cyclic voltammetric (CV) activation, or cleaning procedure.

Amperometric NO gas sensor in the presence of diffusion barrier: selectivity, mass transfer of NO and effect of temperature

Using various PTFE films as diffusion barriers, the mass transfer of nitric oxide and the selectivity in the amperometric NO gas sensor is studied in this paper. The sensitivities of nitric oxide gas sensor are found to be 1.53, 1.56, 1.48 and 1.46 μA ppm −1 by using PTFE films with pore sizes of 0.2, 1.0, 5.0 and 10.0 μm as diffusion barriers, respectively, for gas flow rate greater than 160 ml min −1. The diffusion coefficients of nitric oxide in PTFE diffusion barrier with pore size of 0.2, 1.0, 5.0 and 10.0 μm are found to be 8.57×10 −6, 1.00×10 −5, 1.33×10 −5 and 1.45×10 −5 cm 2 s −1, respectively. The mixing of Knudsen and bulk diffusions is found in the diffusion barrier with 1.0, 5.0 and 10.0 μm pore size and the diffusion of nitric oxide in 0.2 μm pore size of diffusion barrier is mainly contributed by Knudsen diffusion. The sensing current of NO gas sensor is significantly affected by the presence of NO 2 and SO 2. On the other hand, the interference from the humidity, O 2 and CO in the NO gas sensor is insignificant.

Chemiresistor-type NO gas sensor based on nickel phthalocyanine thin films

The sensing characteristics of nickel phthalocyanine (NiPc) thin films for use in a chemiresistor-type nitric oxide gas sensor are discussed. The gas-sensing properties, including current transient, sensitivity, response time, and aging, are studied. A kinetic model proposed in the literature for sensing NO 2 with lead phthalocyanine (PbPc) thin films, in which adsorption involves displacement of surface adsorbed O 2 from a range of heterogeneous sites, can be used to explain our experimental results. It is inferred that exposure to NO concentrations lower than 50 ppm only involves the population of weak adsorption sites, while exposure to NO concentrations higher than 50 ppm may involve the population of stronger adsorption sites. Repeated step changes in NO concentrations of 50 ppm could result in a significant change in response currents within the first five cycles, presumably due to the presence of an irreversible adsorption. Further analysis of current responses reveals that the lower the concentration of NO, the larger the sensitivity. For a lower concentration range, between 5 and 50 ppm NO, the sensitivity lies between 0.41 and 0.42, while for a higher concentration range, between 50 and 500 ppm, the sensitivity decreases to about 0.17 to 0.19.

Amperometric nitric oxide gas sensor: preparation of Au/SPE and sensing behavior

Anion-type (NEOSEPTA®) and cation-type (Nafion®) solid polymeric electrolytes (SPEs) prepared with Au were used as the working electrodes of the amperometric nitric oxide (NO) gas sensor. The decrease in electrochemical activity of the anodic oxidation of NO on Au/NEOSEPTA® was caused by the irreversible adsorptions on the electrode surface. The maximum electrochemical active areas of Au/Nafion® prepared by using N 2H 4·2HCl and NaBH 4 as reducing agents were 140.5 and 200.0 cm 2 when the Au loading were 8.2 and 7.5 mg/cm 2, respectively. The sensitivity of NO gas sensor in the absence of diffusion barrier was 1.33 μA/ppm when Au/Nafion® was used as the working electrode and the gas flow rate was 45 ml/min. Using 0.2 μm PTFE film as a diffusion barrier, the effect of gas flow rate was insignificant and the sensitivity was evaluated as 1.53 μA/ppm with the gas flow rate greater than 150 ml/min. The limiting current of 360 ppm NO decreased from 551 to 75 μA upon continuously operating the NO gas sensor for 119 h.