Nafion Composite Film Research Articles

Solid-state electrochemiluminescence of two iridium(III) complexes

The electrogenerated chemiluminescence (ECL) of two water-insoluble iridium(III) complexes (pq)2Ir(acac)(pq=2-phenyl quinolone anion, acac=acetyl acetonate) and (ppy)2Ir(acac)(ppy=2-phenylpyridine anion) in carbon nanotube (CNT)/Nafion composite films was investigated at a glassy carbon (GC) electrode. CNT and Nafion play significant roles in the iridium(III) complexes immobilization. The excellent chemical stability and electrical conductivity of CNT promote electron transfer. The experimental conditions, such as potential, pH, concentrations of CNT and various coreactants were investigated. The iridium(III) complexes modified electrode had good stability and reproducibility. In our work, the (pq)2Ir(acac)/DBAE (2-(dibutylamino)ethanol) system was used to detect the codeine, one of the many narcotics, and the detection limit was 0.05μM (S/N=3). This method enabled the two water-insoluble iridium(III) complexes to be used for the determination of the analyte in aqueous solution.

A new voltammetric sensor based on poly(L-arginine)/graphene–Nafion composite film modified electrode for sensitive determination of Terbutaline sulfate

A novel voltammetric sensor based on graphene–Nafion and poly(L-arginine) was constructed by electrodeposited and simple dipping–drying methods and used for high-sensitive determination of Terbutaline sulfate (TBS). The resulting poly(L-arginine)/graphene–Nafion modified electrode showed a significant voltammetric response to TBS due to the synergistic effect of poly(L-arginine) and graphene–Nafion, in which poly(L-arginine) had electrocatalytic ability for TBS and graphene provided a large specific surface area, excellent electric conductivity and electrocatalytic activity. The sensor gave a good linear range over 4.0×10−8–5.0×10−6molL−1 with a detection limit of 1.2×10−8molL−1 towards the determination of TBS. The high sensitivity and selectivity together with the good linear relationship, very easy surface regeneration and good stability at such a modified electrode led us to construct a practical TBS biosensor successfully. This work promoted the potential applications of graphene-based materials in electrochemical sensors.

High sensitive determination of theophylline based on gold nanoparticles/l-cysteine/Graphene/Nafion modified electrode

In the work described on this paper, a gold nanoparticles (GNP)/l-cysteine (l-cys)/Graphene (Gr)/Nafion composite film modified glass carbon electrode (GCE) was fabricated and characterized. The modified electrode showed excellent electrocatalytic activity towards the oxidation of theophylline (TP) in 0.1molL−1 H2SO4 medium. Differential pulse voltammetry (DPV) was used for the determination of TP. Under the optimum conditions, the peak current of TP was proportional to its concentration at the range of 4.0×10−9 to 6.0×10−5molL−1 with a detection limit 4.0×10−10molL−1. The newly developed method was successfully applied for the determination of TP in tea samples and pharmaceutical tablets with good percentage of recoveries.

Amperometric Vitamin C Biosensor Based on the Immobilization of Ascorbate Oxidase into the Biocompatible Sandwich-Type Composite Film

Ascorbate oxidase (AO), a biologically active macromolecule, was successfully immobilized into a biocompatible sandwich-type composite film for developing the vitamin C (VC) biosensor, and the content of VC in commercial juices was amperometrically determined. The biocompatible and conducting poly(3,4-ethylenedioxythiophene) composite film and highly stable and selective multiwalled carbon nanotubes -Nafion composite film were prepared as inner and outer films of biosensor. AO molecules were immobilized between these two composite films. The as-fabricated biosensor displayed an excellent bioelectrocatalytic performance towards the oxidation of VC, a fast current response, a low working potential, a high sensitivity, a wide linear range, and a low detection limit. Moreover, the working mechanism of the biosensor was proposed, and its kinetics was also discussed. In addition, the specificity, reproducibility, and feasibility of the as-fabricated biosensor were also evaluated. Good results of the VC determination in commercial juices indicated that the as-fabricated biosensor was a potential candidate for the electrochemical determination of VC in agricultural crops. Inner and outer films provided a promising platform for the immobilization of biologically active species.

Electrochemical oxidation behavior of methotrexate at DNA/SWCNT/Nafion composite film-modified glassy carbon electrode

Glassy carbon electrode modified with DNA-functionalized single-walled carbon nanotube (DNA/SWCNT) and Nafion composite film was developed for the detection of methotrexate. The characteristics of the modified electrode were examined by transmission electron microscopy and cyclic voltammetry. Compared with a bare glassy carbon electrode and Nafion- and SWCNT/Nafion-modified electrodes, the DNA/SWCNT/Nafion-modified one exhibited the more superior ability of detecting methotrexate, including the higher sensitivity and the lower overpotentials, due to the synergetic DNA-functionalized SWCNT and Nafion. Also, the dependence of the current on pH, nature of buffer, instrumental parameters, accumulation time, and potential was investigated to optimize the experimental conditions in the determination of methotrexate. Under the selected conditions, the modified electrode in pH = 2.78 Britton–Robinson buffer solutions showed a linear voltammetric response to methotrexate within the concentration range of 2.0 × 10−8–1.5 × 10−6 mol L−1, with the detection limit of 8.0 × 10−9 mol L−1. The method was also applied to detect methotrexate in medicinal tablets and spiked human blood serum samples.

Wettability of Nafion and Nafion/Vulcan Carbon Composite Films

The wettability of the Pt/carbon/Nafion catalyst layer in proton exchange membrane fuel cells is critical to their performance and durability, especially the cathode, as water is needed for the transport of protons to the active sites and is also involved in deleterious Pt nanoparticle dissolution and carbon corrosion. Therefore, the focus of this work has been on the first-time use of the water droplet impacting method to determine the wettability of 100% Nafion films, as a benchmark, and then of Vulcan carbon (VC)/Nafion composite films, both deposited by spin-coating in the Pt-free state. Pure Nafion films, shown by SEM analysis to have a nanochanneled structure, are initially hydrophobic but become hydrophilic as the water droplet spreads, likely due to reorientation of the sulfonic acid groups toward water. The wettability of VC/Nafion composite films depends significantly on the VC/Nafion mass ratios, even though Nafion is believed to be preferentially oriented (sulfonate groups toward VC) in all cases. At low VC contents, a significant water droplet contact angle hysteresis is seen, similar to pure Nafion films, while at higher VC contents (>30%), the films become hydrophobic, also exhibiting superhydrophobicity, with surface roughness playing a significant role. At >80% VC, the surfaces become wettable again as there is insufficient Nafion loading present to fully cover the carbon surface, allowing the calculation of the Nafion:carbon ratio required for a full coverage of carbon by Nafion.

Myoglobin within graphene oxide sheets and Nafion composite films as highly sensitive biosensor

A highly sensitive biosensor was fabricated by incorporating myoglobin (Mb) within graphene oxide (GO) sheets and Nafion composite films. The stable composite Mb–GO–Nafion films were characterized by electrochemistry, scanning electron microscopy, Fourier transform infrared spectroscopy and UV–vis spectroscopy. It was found that Mb in Mb–GO–Nafion films retained its secondary structure similar to its native states. Cyclic voltammetry of Mb–GO–Nafion films showed a pair of well defined, quasi-reversible peaks at about −0.312V vs saturated calomel electrode (SCE) at pH 5.5, corresponding to direct electron transfer (DET) between Mb and the glassy carbon electrode. Electrochemical parameter of Mb in Mb–GO–Nafion film such as apparent heterogeneous electron transfer rate constant (ks) and formal potential (Eo′) were obtained. The dependence of Eo′ on solution pH indicated that the DET reaction of Mb was coupled with proton transfer. Mb in the films displayed good electrocatalytic activities towards various substrates such as hydrogen peroxide, nitrite and oxygen, indicating that the composite films have potential applications in fabricating novel biosensors without using mediators.

Label-free electrochemiluminescent immunosensor for α-fetoprotein: performance of Nafion–carbon nanodots nanocomposite films as antibody carriers

A simple and highly sensitive electrochemiluminescent immunosensor based on nanocomposite architecture of the one-pot synthesized carbon nanodots and Nafion composite film was proposed for the detection of α-fetoprotein.

A Novel Electrochemiluminescence Electrospun Carbon Nanofiber Based Sensor for Atropine

Abstract A novel electrochemiluminescence (ECL) sensor based on tris(2,2′-bipyridyl) ruthenium(II) (Ru(bpy) 3 2+ )/electrospun carbon nanofiber (CNF)/Nafion composite films was demonstrated for the determination of atropine. The voltammetric and ECL behaviors of the presented sensor were investigated. The results indicated that the addition of CNF in the composite films could increase the current and ECL intensity of Ru(bpy) 3 2+ , which were subjected to diffusion-controlled processes. Under optimal experimental conditions, the proposed ECL sensor exhibited a wide linear range ( r = 0.9967) of 1 × 10 −7 –1 × 10 −4 M with a detection limit ( S/N = 3) of 1 × 10 −7 M for atropine. The relative standard deviation for 1 × 10 −5 M atropine is 2.86% ( n = 7), and the present ECL sensor displayed outstanding stability. The ECL sensor was also utilized for the determination of atropine in urine samples, and the recovery was in the range of 81%–88%.

Synthesis of polypyrrole–Nafion composite films by gas phase electroformation

Nafion was introduced into polypyrrole (PPy) matrix by gas phase electrochemical polymerisation. This produced a uniform, homogeneous and conductive thin film of composite polymer. The films (PPy/Nafion) also show surface features of highly ordered structural regularity. The composites obtained were characterised by cyclic voltammetry (CV) and redox performance were investigated. The relationship of the anodic current of the composite with the various experimental parameters such as concentration of Nafion, current density, polymerisation time and temperature were investigated. Anodic current increases with the Nafion concentration, polymerising time, temperature and current density.

A Solid‐State Electrochemiluminescence Immunosensor Based on MWCNTs‐Nafion and Ru(bpy)32+/Nano‐Pt Nanocomposites for Detection of α‐Fetoprotein

AbstractA approach was successfully employed for constructing a solid‐state electrochemiluminescence (ECL) immunosensor by layer‐by‐layer self‐assembly of multiwall carbon nanotubes (MWCNTs)‐Nafion composite film, Ru(bpy)32+/nano‐Pt aggregates (Ru‐PtNPs) and Pt nanoparticles (PtNPs). The influence of Pt nanoparticles on the ECL intensity was quantitatively evaluated by calculating the electroactive surface area of different electrodes with or without PtNPs to immobilize Ru(bpy)32+. The principle of ECL detection for target α‐fetoprotein antigen (AFP) was based on the increment of resistance after immunoreaction, which led to a decrease in ECL intensity. The linear response range was 0.01–10 ng mL−1 with the detection limit of 3.3 pg mL−1. The immunosensor exhibited advantages of simple preparation and operation, high sensitivity and good selectivity.

Sensitive Voltammetric Detection of Trace Heavy Metals in Real Water Using Multi-Wall Carbon Nanotubes/Nafion Composite Film Electrode

Multi-wall carbon nanotubes (MWCNTs) and Nafion composite film (MWCNTs/Nafion) were used for fabricating electrochemical sensors for the voltammetric detection of trace lead(II) and cadmium(II) in several water samples. The morphology and structure of MWCNTs/Nafion film were characterized by scanning electron microscopy (SEM) and infrared spectrum (IR). The electron transfer of MWCNTs/Nafion composite film was examined by cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS). Various experimental parameters, which influenced the response of MWCNTs/Nafion/GC to target metals, were optimized. The results showed that the synergistic effect was obtained on the MWCNTs/Nafion/GC whose sensitivity and stability were better than those of Nafion-coated electrode (Nafion/GC) or CNTs/GC. Stability of the Pb(II) and Cd(II) stripping signals was excellent with relative standard deviations (RSD) within 5% (n=10) from one electrode preparation to another, and RSD of 30 µg·L−1 Pb(II) and Cd(II) were 2.8% and 3.2% for 20 repeated analysis on one single CNTs/Nafion/GC. Over 50 runs, the stability of Pb and Cd detection at the MWCNTs/Nafion conposites electrode was still satisfactory with RSD lower than 6.0%. The determination limits (S/N=3) of the proposed method were determined to be 100 ng·L−1 for Pb and 150 ng·L−1 for Cd. Finally, the MWCNTs/Nafion/GC was successfully applied to determine Pb(II) and Cd(II) in different water samples with recoveries of 97%–103% for Pb and 96%–104% for Cd.

Flow injection measurements of S-nitrosothiols species in biological samples using amperometric nitric oxide sensor and soluble organoselenium catalyst reagent.

A novel flow injection analysis (FIA) system suitable for measurement of S-nitrosothiols (RSNOs) in blood plasma is described. In the proposed (FIA) system, samples and standards containing RSNO species are injected into a buffer carrier stream that is mixed with the reagent stream containing 3,3'-dipropionicdiselenide (SeDPA) and glutathione (GSH). SeDPA has been shown previously to catalytically decompose RSNOs in the presence of a reducing agent, such as GSH, to produce nitric oxide (NO). The liberated NO is then detected downstream by an amperometric NO sensor. This sensor is prepared using an electropolymerized m-phenylenediamine (m-PD)/resorcinol and Nafion composite films at the surface of a platinum electrode. Using optimized flow rates and reagent concentrations, detection of various RSNOs at levels in the range of 0.25-20 μM is possible. For plasma samples, detection of background sensor interference levels within the samples must first be carried out using an identical FIA arrangement, but without the added SeDPA and GSH reagents. Subtraction of this background sensor current response allows good analytical recovery of RSNOs spiked into animal plasma samples, with recoveries in the range of 90.4-101.0%.

Amperometric Tyrosinase Biosensor Based on Carbon Nanotube‐Doped Sol‐Gel‐Derived Zinc Oxide–Nafion Composite Films

AbstractA highly sensitive amperometric tyrosinase biosensor has been developed based on mesoporous composite films of carbon nanotube (CNT)–ZnO–Nafion composite film encapsulating tyrosinase on a glassy carbon electrode. Due to the mesoporous nature (diameter: 3.17 nm) of the composite film, the biosensor exhibits very fast response time of 2 s. The present biosensor shows an excellent sensitivity of 766 mA/M and a detection limit of 4.7×10−8 M (S/N=3) for phenol. The biosensor retains 88 % of its initial activity after 2 weeks of storage in 50 mM phosphate buffer at pH 7.0. The present biosensor exhibits good recovery for the spiked phenol in an industrial waste water sample.

Electrochemical oxidation behavior of colchicine on a graphene oxide-Nafion composite film modified glassy carbon electrode

An electrochemical sensor, based on a graphene oxide (GO)-Nafion composite film modified glassy carbon electrode (GCE), was developed and used for detection of trace amounts of colchicine. Owing to the large surface area, good conductivity of GO and good affinity of Nafion, the sensor exhibited excellent electrocatalytic activity for the oxidation of colchicine, displaying a wide linear response from 5.0 × 10(-8) to 2.0 × 10(-5) mol L(-1) and a low detection limit of 1.5 × 10(-8) mol L(-1) in 0.1 mol L(-1) H(2)SO(4) solution. And this modified electrode exhibited a superior immunity from epinephrine, dopamine and ascorbic acid interference. The method was also applied successfully to detect colchicine in medicinal tablets.

Single-walled carbon nanotube/Nafion composites as methanol sensors

Single-walled carbon nanotube (SWCNT)/Nafion composite films were fabricated on an interdigitated electrode by using a simple casting method. Nafion acts as a polymer backbone to give stable and homogeneous cast thin films. The potential use of the composites as sensors of methanol concentration in water was investigated. The composites are operative even at ambient temperatures, and respond quickly to concentration changes. The resistance increases significantly with increasing concentration between 0.5 M and 4 M. The composites may be useful as a material to measure the concentration of methanol for direct fuel cells.

Fabrication of Chemiluminescence Sensor Based on Conducting Polymer@SiO2/Nafion Composite Film

Tris(2,2'-bipyridyl)ruthenium (II) (Ru(bpy)2+) electrogerated chemiluminescence (ECL) sensor was fabricated by immobilization of Ru(bpy)2+ complex on conducting polymer@SiO2/Nafion composite film on surface of glassy carbon electrode. The conducting polymer@SiO2 nanocomposites were prepared by coating polyaniline (PANI), polypyrrole (PPy), and polythiophene (PTh) on the surface of the SiO2 sphere. The conducting polymer@SiO2 nanocomposite was characterized by scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and atomic force microscopy (AFM). The sensitivity and reproducibility of the prepared ECL sensor to tripropylamine (TPA) was evaluated. As a result, the PPy@SiO2 composite electrode exhibited high sensitivity and good reproducibility compared to that obtained with PANI@SiO2 and PTh@SiO2 composite electrodes because of the strong interaction between PPy@SiO2 and Ru(bpy)2+ complex.

Electrochemical oxidation behavior of guanine and adenine on graphene–Nafion composite film modified glassy carbon electrode and the simultaneous determination

The electrochemical behavior of guanine and adenine on the graphene and Nafion composite film modified glassy carbon electrode was investigated by differential pulse voltammetry (DPV). The results indicated that the modified electrode exhibited an excellent electrocatalytic activity towards the oxidation of guanine and adenine, testified by the increased oxidation peak current and decreased oxidation potential. The experimental conditions were optimized. The separation of the two oxidation peaks was 0.364 V in 0.1 M pH 4.4 acetate buffer solution (ABS). Based on this, a novel electrochemical method was proposed to simultaneously determine guanine and adenine with the detection limit of 0.58 (guanine) and 0.75 (adenine) μM (S/N = 3). The proposed method was applied to determine guanine and adenine in milk powder, urine and herring sperm DNA samples with satisfactory results. The value of (G + C)/(A + T) in herring sperm DNA was calculated to be 0.8065. The fabricated electrode showed excellent reproducibility, stability and anti-interference.

Tris(2,2′‐bipyridyl)ruthenium(II) Electrogenerated Chemiluminescence Sensor Based on Platinized Carbon Nanotube–Zirconia–Nafion Composite Films

AbstractMesoporous films of platinized carbon nanotube–zirconia–Nafion composite have been used for the immobilization of tris(2,2′‐bipyridyl)ruthenium (II) (Ru(bpy)32+) on an electrode surface to yield a solid‐state electrogenerated chemiluminescence (ECL) sensor. The composite films of Pt–CNT–zirconia–Nafion exhibit much larger pore diameter (3.55 nm) than that of Nafion (2.82 nm) and thus leading to much larger ECL response for tripropylamine (TPA) because of the fast diffusion of the analyte within the films. Due to the conducting and electrocatalytic features of CNTs and Pt nanoparticles, their incorporation into the zirconia–Nafion composite films resulted in the decreased electron transfer resistance within the films. The present ECL sensor based on the Pt–CNT–zirconia–Nafion gave a linear response (R2=0.999) for TPA concentration from 3.0 nM to 1.0 mM with a remarkable detection limit (S/N=3) of 1.0 nM, which is much lower compared to those obtained with the ECL sensors based on other types of sol‐gel ceramic–Nafion composite films such as silica–Nafion and titania–Nafion.

Direct electrochemistry of hemoglobin in a nafion and CuS microsphere modified carbon ionic liquid electrode and its electrocatalytic behavior

Direct electrochemistry of hemoglobin (Hb) was realized on a Nafion and CuS microsphere composite film modified carbon ionic liquid electrode (CILE) with N-butylpyridinium hexafluorophosphate (BPPF6) as binder. Scanning electron microscopy (SEM), UV-Vis absorption spectroscopy and cyclic voltammetry were used to characterize the fabricated Nafion/CuS/Hb/CILE. Experimental results showed that a pair of well-defined quasi-reversible redox peaks appeared with the formal potential as -0.386 V (vs. SCE) in pH 7.0 Britton-Robinson (B-R) buffer solution, which was attributed to the Hb heme Fe(III)/Fe(II) redox couples. The electrochemical parameters of Hb in the composite film were carefully investigated with the charge transfer coefficient (α), the electron transfer number (n) and the electron transfer rate constant (ks) as 0.505, 1.196 and 0.610 s -1 , respectively. The composite film provided a favorable microenvironment for retaining the native structure of Hb. The presence of CuS microspheres showed great improvement on the electron transfer rate of Hb with the CILE, which maybe due to the contribution of specific characteristics of CuS microspheres and the inherent advantages of ionic liquid on the modified electrode. The fabricated Hb modified electrode showed good electrocatalytic ability in the reduction of H2O2. The proposed bioelectrode can be used as a new third generation H2O2 biosensor.