Solid-state electrochemiluminescence sensor based on the Nafion/poly(sodium 4-styrene sulfonate) composite film

An effective electrochemiluminescence (ECL) sensor based on Nafion/poly(sodium 4-styrene sulfonate) (PSS) composite film-modified ITO electrode was developed. The Nafion/PSS/Ru composite film was characterized by atomic force microscopy, UV-vis absorbance spectroscopy and electrochemical experiments. The Nafion/PSS composite film could effectively immobilize tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) via ion-exchange and electrostatic interaction. The ECL behavior of Ru(bpy)₃²⁺ immobilized in Nafion/PSS composite film was investigated using tripropylamine (TPA) as an analyte. The detection limit (S/N = 3) for TPA at the Nafion/PSS/Ru composite-modified electrode was estimated to be 3.0 nM, which is 3 orders of magnitude lower than that obtained at the Nafion/Ru modified electrode. The Nafion/PSS/Ru composite film-modified indium tin oxide (ITO) electrode also exhibited good ECL stability. In addition, this kind of immobilization approach was simple, effective, and timesaving.     

Wide- and narrow-rim functionalised calix[4]arenes: synthesis and characterisation

Functionalisation of calix[4]arene at both the wide and narrow rims leads to the formation of compounds containing bipyridyl, via an amide linkage, at the wide rim and having either a butyl chain, a benzyl group or an alkyl ester functionality at the narrow rim. All compounds were characterised using ¹H and ¹³C NMR spectroscopies. Initial binding studies with Ru(bipy)₂Cl₂ are reported.     

Electrocatalytic Oxidation of Ethanol on Graphite Electrodes Coated with a Nafion Film with Incorporated Particles of Ruthenium or Its Complexes

The electrochemical behavior of ethanol on graphite electrodes with a Nafion film containing ruthenium as a crystalline metal deposit or a metal complex was compared. It was found that, in the oxidation of ethanol, aqua and phenanthroline complexes of ruthenium(III) incorporated in the Nafion film exhibit catalytic activity. A larger catalytic effect was observed at an electrode containing the Ru(phen) ₃ ³⁺ complex. A procedure is proposed for the voltammetric determination of ethanol at this electrode.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 603–609.Original Russian Text Copyright © 2005 by Shaidarova, Gedmina, Chelnokova, Budnikov.Presented at the VI All-Russian Conference (with International Participation) on Electrochemical Methods of Analysis (EMA-2004, Ufa, May 23–27, 2004).     

Effects of Humidity,Temperature and Bismuth Electrodeposition on Electroanalytical Performances of Nafion‐coated Printed Electrodes for Cd2+ and Pb2+ Detection

The synergistic use of Nafion polymeric membrane and in situ electrodeposited bismuth film is a worthwhile strategy to develop electrochemical sensors for the detection of Cd²⁺ and Pb²⁺. However, Nafion thin films morphological and conductivity properties have a strong dependence on the environmental conditions, such as relative humidity and temperature, while the bismuth in situ electroplating can affect the repeatability of measurements. With the aim to overcome these drawbacks, the effects of the storage environmental conditions were investigated to improve the morphological stability and electroanalytical performances of Nafion film‐based sensor for the detection of Cd²⁺ and Pb²⁺. Nafion‐coated graphite‐based screen‐printed electrodes were stored at different humidity and temperature conditions and characterised by using square wave anodic stripping voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Significant differences were observed at the varying of humidity conditions, with an enhancement of sensor electrochemical performances at lower humidity. Furthermore, different approaches for bismuth in situ electrodeposition on Nafion‐coated screen‐printed electrodes were compared by using overlap or removal approach. This study disclosed considerable differences in the electrochemical performances and morphology of the resulting bismuth‐sensor, obtaining an enhancement of the working stability for the removal approach.     

A novel amperometric sensor and chromatographic detector for determination of parathion

A novel amperometric sensor and chromatographic detector for determination of parathion has been fabricated from a multi-wall carbon nano-tube (MWCNT)/Nafion film-modified glassy-carbon electrode (GCE). The electrochemical response to parathion at the MWCNT/Nafion film electrode was investigated by cyclic voltammetry and linear sweep voltammetry. The redox current of parathion at the MWCNT/Nafion film electrode was significantly higher than that at the bare GCE, the MWCNT-modified GCE, and the Nafion-modified GCE. The results indicated that the MWCNT/Nafion film had an efficient electrocatalytic effect on the electrochemical response to parathion. The peak current was proportional to the concentration of parathion in the range 5.0×10^–9–2.0×10^–5 mol L^–1. The detection limit was 1.0×10^–9 mol L^–1 (after 120 s accumulation). In high-performance liquid chromatography with electrochemical detection (HPLC–ED) a stable and sensitive current response was obtained for parathion at the MWCNT/Nafion film electrode. The linear range for parathion was over four orders of magnitude and the detection limit was 6.0×10^–9 mol L^–1. Application of the method for determination of parathion in rice was satisfactory.     

Dissociation of disulfide‐intact somatostatin ions: the roles of ion type and dissociation method

The dissociation chemistry of somatostatin‐14 was examined using various tandem mass spectrometry techniques including low‐energy beam‐type and ion trap collision‐induced dissociation (CID) of protonated and deprotonated forms of the peptide, CID of peptide‐gold complexes, and electron transfer dissociation (ETD) of cations. Most of the sequence of somatostatin‐14 is present within a loop defined by the disulfide linkage between Cys‐3 and Cys‐14. The generation of readily interpretable sequence‐related ions from within the loop requires the cleavage of at least one of the bonds of the disulfide linkage and the cleavage of one polypeptide backbone bond. CID of the protonated forms of somatostatin did not appear to give rise to an appreciable degree of dissociation of the disulfide linkage. Sequential fragmentation via multiple alternative pathways tended to generate very complex spectra. CID of the anions proceeded through CH₂? S cleavages extensively but relatively few structurally diagnostic ions were generated. The incorporation of Au(I) into the molecule via ion/ion reactions followed by CID gave rise to many structurally relevant dissociation products, particularly for the [M+Au+H]²⁺ species. The products were generated by a combination of S? S bond cleavage and amide bond cleavage. ETD of the [M+3H]³⁺ ion generated rich sequence information, as did CID of the electron transfer products that did not fragment directly upon electron transfer. The electron transfer results suggest that both the S? S bond and an N? C_α bond can be cleaved following a single electron transfer reaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Electrochemical evaluation of avidin-biotin interaction using N-iodoacetyl-N-biotinylhexylenediamine

The avidin-biotin assay was investigated by an electrochemical procedure based on the chemical reaction between cysteine containing a thiol group and N-iodoacetyl-N-biotinylhexylenediamine (IB). In the presence of avidin and biotin this reaction, whereby the thiol group combines with IB, is controlled because IB has a biotin part; that is, avidin and biotin are detected indirectly by measurement of iodide ion or cysteine. To achieve a high sensitivity of detection, Hg(II) was introduced as a marker that interacts with cysteine and the oxidation peak from Hg(0) to Hg(II) was measured. The sensitivity of detection of avidin was at the level of 10⁻⁹ M. The relative standard deviation at 1 × 10⁻⁸ M avidin was 4.8% (n = 5). On the other hand, a response curve to detect biotin was obtained by the competitive reaction between IB and biotin for the limited binding sites of avidin. The change in peak current enables the detection of biotin at the level of 10⁻⁹ M. This method has the advantage that it is not necessary to separate free IB from bound IB.     

Properties of glucose sensors prepared by the electropolymerization of a positively charged pyrrole derivative

Amperometric glucose sensors were prepared by electropolymerization of a pyrrole derivative having the positively charged group, 3-(1-pyrrolyl)propyltrimethylammonium bromide, in the presence of glucose oxidase on bare and Nafion-coated platinum electrodes. Linear relationships between the glucose concentration and the response current for the electrode with and without Nafion inner film were up to 10.0 and 6.0 mmol dm⁻³, respectively. The introduction of Nafion inner film lowered the influence of electroactive compounds, such as ascorbic acid, uric acid, and acetoaminophen, on the sensor response, but was not able to eliminate the influence of these compounds sufficiently. However, Nafion inner film was effective in increasing the electrode stability. The response current of the electrode with Nafion film remained stable for more than 50 days, while that without Nafion film was significantly reduced after 20 days of use.     

Novel sulphonated poly (vinyl chloride)/poly (2-acrylamido-2-methylpropane sulphonic acid) blends-based polyelectrolyte membranes for direct methanol fuel cells

Proton-conducting and methanol barrier properties of the proton exchange membrane (PEM), as well as the high cost of direct methanol fuel cell (DMFC) components, are the key determinants of the performance and commercialization of DMFCs. Therefore, this study aimed to develop cost- and performance-effective membranes based on sulphonated poly (vinyl chloride) (SPVC)/poly (2-acrylamido-2-methyl-1-propane sulphonic acid) (PAMPS) blends. Such membranes have been simply prepared by blending SPVC and PAMPS solutions, followed by solvent evaporation via casting. Interaction of SPVC with PAMPS was confirmed by different characterization techniques such as Fourier Transform Infra-red (FTIR) and Raman scattering spectroscopy in which the two characteristic absorption bands of sulfonic groups appeared at 1093 and 1219 cm⁻¹ additionally, strong peaks at around 1656 cm⁻¹ attributed to vibration of amide groups of PAMPS portion in the polymer blend. Furthermore, the interaction of SPVC with PAMPS improves the thermal properties along with ion exchange capacity in turn decreasing the methanol permeability through the membrane in comparison with the SPVC membrane. The IEC of PVC and Nafion 117 membranes were 1.25, 0.91 meq/g; respectively. And the maximum water uptake of PVC and Nafion 117 membranes were 75 and 65.44%; respectively. Methanol permeability value of 7.7 × 10⁻⁷ cm²/s which was noticeably lower than the corresponding value recorded for Nafion® (3.39 × 10⁻⁶ cm²/s). Therefore, these fabricated membranes can be considered a low-cost efficient candidate for use in DMFC, especially for its capability to resolve the methanol cross-over issue.     

Fe(CN)64−‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Electrode. Part 2: Stability Improvement and Selective Detection of Dopamine in the Presence of Ascorbic Acid

Highly stable Nafion‐covered hexacyanoferrate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Fe(CN)₆^4?/Naf) film modified glassy carbon electrode (GCE), for the selective detection of dopamine (DA) in the presence of ascorbic acid (AA), was prepared by first ion‐exchanging Fe(CN)₆^4? into PLL‐GA coating on GCE then sealing it with a Nafion outer layer. The Nafion over layer is crucial in preventing leaching of Fe(CN)₆^4? ions from the inner layer. The first layer was acting as electrocatalyst for DA oxidation and the outer coating acted as discriminating layer for selective permeation of DA in the presence of interfering anionic species. More than 90% of the initial response was retained after coating with the Nafion protecting layer compared to a huge loss (>60%) without Nafion outer layer. 5% Nafion coating was identified as optimum thickness for the selective detection of DA in the presence of AA.     

Electrocatalytic Nitrite Reduction to Nitrogen Oxide by a Synthetic Analogue of the Active Site of Cu‐Containing Nitrite Reductase Incorporated in Nafion Film

The electrocatalytic reduction of nitrite to NO by [CuMe₂bpa(H₂O)(ClO₄)]⁺ ( 1 ), which is a model for the active site of copper‐containing nitrite reductase, incorporated in Nafion film was investigated. The Cu complex in the Nafion matrix exhibits an intense band at 267 nm and a broad band around 680 nm, assigned to d–d and ligand field transitions, respectively. The 77‐K EPR spectrum of 1 in the Nafion matrix reveals the typical axial signals (g_//=2.28, g =2.08, A_//=13.3 mT) of a tetragonal Cu²⁺ chromophore. The redox potential, which is related to the Cu⁺/Cu²⁺ couple, was ?146 mV (ΔE=72 mV) at pH 5.5. The redox reaction of 1 in Nafion was not dependent on pH and was a diffusion‐controlled process. The electronic structure and redox properties of 1 in the negatively charged polymer matrix were almost the same as those in aqueous solution. In the presence of nitrite, an increase in the cathodic current was observed in the cyclic voltammogram of 1 in the Nafion matrix. The current increase was dependent on the nitrite concentration and pH in solution. Upon reaching ?400 mV, a linear generation of NO was observed for the 1 /Nafion film coated electrode. The relationship between the rate of NO generation and the nitrite concentration in solution was analyzed with the Michaelis–Menten equation, where V_max=45.1 nM s^?1 and K_m=15.8 mM at pH 5.5. The Cu complex serves the function of both the catalyst and electron transport in the Nafion matrix. The sensitivity of the electrode was estimated to be 3.23 μA mM^?1 in the range of 0.1–0.4 mM nitrite.     

Electrochemical characterization of PANI-Nafion membranes and their electrocatalytic activity

PANI-Nafion^® membranes were prepared by a chemical method in which the faces of a commercial Nafion membrane were contacted with two acid solutions containing an oxidant (Fe³⁺) and aniline respectively. They were then characterized by a variety of electrochemical techniques (cyclic voltammetry, chronoamperometry, ac impedance). PANI was stored mostly in the vicinity of the Nafion face exposed to the oxidant. When this face was contacted with Hg and the other with electrolyte solutions, typical electrochemical responses of PANI were detected. Electrocatalytic reduction of O₂ and oxidation of N₂H₄ were achieved on PANI-Nafion electrodes and found to be only slightly slowed down with respect to ordinary PANI film electrodes, at variance with a fast process such as Fe³⁺ reduction, the rate of which was severely limited by diffusion through the membrane.     

Fabrication of a New Electrochemiluminescent Sensing Interface Based on Zinc Oxide Nanorod

A new electrochemiluminescence (ECL) sensing interface was established based on the zinc oxide nanorod in this paper. Firstly, the zinc oxide (ZnO) nanorod was prepared on an indium tin oxide (ITO) electrode surface by the method of constant current cathodic electrodeposition, on which the Nafion film was then modified, and finally ruthenium(II) tris(bipyridine) (Ru(bpy)₃²⁺) was immobilized at the ZnO nanorod/Nafion composite‐modified electrode. The sensing interface shows well ECL behaviors and perfect stability after being constant temperature treatment at 80 °C. The composite electrode was characterized by EIS, SEM and XRD. The results showed that the good stability maybe related to the water content of Nafion film.     

Fabrication and characterization of supported dual acidic ionic liquids for polymer electrolyte membrane fuel cell applications

In this study, we proposed an innovative and versatile method for preparation of highly stable and conductive supported ionic liquid (IL) membranes for proton exchange fuel cell applications. Novel covalently supported dual acidic IL membranes were prepared by radiation induced grafting of 4-vinyl pyridine (4-VP) onto poly(ethylene-co-tetrafluoroethylene) (ETFE) film followed by post-functionalization via sequential treatments with 1,4-butane sultone and sulfuric acid to introduce pyridinium alkyl sulfonate/hydrogen sulfate moieties. The advantage of our approach lies in grafting polymers with highly reactive functional groups suitable for efficient post-sulfonation. The membranes displayed better swelling and mechanical properties compared to Nafion 112 despite having more than 3 times higher ion exchange capacity (IEC). The proton conductivity reached superior values to Nafion above 80 °C. Particularly, the membrane with ion exchange capacity of 3.41 displayed a proton conductivity of 259 mScm⁻¹ at 95 °C. This desired conductivity value is attributed to the high IEC of the membranes as well as dissociation of the hydrophobic ETFE polymer and hydrophilic pyridinium alkyl sulfonate groups. Such appealing properties make the supported IL membranes promising for proton exchange membrane fuel cells (PEMFC).     

Cobaltocenium Carboxylate Transition Metal Complexes: Synthesis,Structure, Reactivity,and Cytotoxicity

Cobaltocenium carboxylate is an unusual betaine that functions as a formally neutral carboxylate ligand with late transition metal centers comprising Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Rh⁺. Structurally, a rich coordination chemistry is observed – from simple monomeric homoleptic complexes to heteroleptic dimeric, trimeric, and polymeric compounds, as shown by X‐ray diffraction of 11 compounds. Chemically, thermal decarboxylation was investigated aiming at the formation of cobaltocenium‐carbene transition metal complexes, in analogy to such chemistry of imidazolium carboxylate betaines. Cytotoxicity studies of cobaltocenium carboxylate transition metal complexes were performed to evaluate the medicinal bioorganometallic potential of these compounds. While cobaltocenium carboxylate was inactive, its complexes with Ag⁺, Cd²⁺, and Hg²⁺ triggered significant cytotoxic effects.     

Amperometric Ethanol Biosensor Based on Carbon Nanotubes Dispersed in Sol–Gel‐Derived Titania–Nafion Composite Film

Composite solution of sol–gel‐derived titania and perfluorosulfonated ionomer (Nafion) was used as a solubilizing agent for multiwalled carbon nanotubes (CNT) as well as an encapsulation matrix for alcohol dehydrogenase (ADH) for the fabrication of a highly sensitive and stable amperometric ethanol biosensor. ADH was immobilized within a thin film of CNT–titania–Nafion composite film coated on a glassy carbon electrode. Because of the mesoporous nature of the CNT–titania–Nafion composite film, the present biosensor exhibited remarkably fast response time within 2 s. The presence of CNT in the composite film increases not only the sensitivity of the ethanol biosensor but also the long‐term stability of the biosensor. The present biosensor responds linearly to ethanol in the wide concentration ranges from 1.0×10^?5 M to 3.0×10^?3 M with the sensitivity of 51.6 mA M^?1cm^?2. The present biosensor showed good long‐term stability with 75% of its activity retained after 4 weeks of storage in 50 mM phosphate buffer at pH 7.0.     

Disposable Nafion-modified micro-fabricated bismuth-film sensors for voltammetric stripping analysis of trace metals in the presence of surfactants

This work is a study of the analytical utility of Nafion-modified microfabricated bismuth film electrodes (BiFEs) for the determination of Pb(II) and Cd(II) by anodic stripping voltammetry (ASV) in the presence of surfactants. Micro-fabricated BiFEs were prepared by depositing a thin film of bismuth on the surface of a silicon substrate by sputtering while the two-dimensional geometry of the final sensors was defined by photolithography. The BiFEs were further drop-coated with a Nafion film. These devices were applied to the determination of Pb(II) and Cd(II) by square wave ASV (SWASV) in the presence of Triton X-100 (a non-ionic surfactant), cetyltrimethylammonium bromide (CTAB) (a cationic surfactant) and sodium dodecyl sulphate (SDS) (an anionic surfactant). It was found that the presence of Nafion afforded an increase in sensitivity and the tolerance against surfactants but these properties were severely influenced by both the thickness of the Nafion film and the nature of the interfering surfactant. Using a Nafion of 0.4 μm thickness and 120 s of preconcentration, the repeatability (expressed as the % relative standard deviation on the same sensor (n = 8)) at the 20 μg l⁻¹ level was 3.8% for Pb(II) and 3.1% for Cd(II) and the limits of detection were 0.5 μg l⁻¹ for Cd(II) and Pb(II). The sensors were applied to Cd(II) and Pb(II) determination in a certified lake-water sample.     

Preparation of highly porous heat-resistant polybenzoxazole network films and their electrical conductivities

Highly porous rigid polybenzoxazole (PBO) network films were prepared using a precursor-mediated fabrication method. The obtained PBO network films possessed high porosities of ~40%, as calculated from their apparent densities. In addition, the 5%-weight-loss temperatures of the films were ≥570°C under nitrogen atmosphere, demonstrating an excellent thermal stability. The electrical conductivities of the obtained PBO network films and phosphoric-acid-doped PBO network films were also evaluated. In addition, PBO network films containing pyridine rings were prepared and subjected to phosphoric acid doping. The resultant films were found to exhibit the highest conductivities of the films considered in this study owing to proton conduction both between phosphate groups and between the pyridine rings. The highest conductivity was found for a film prepared from a phosphoric-acid-doped PBO network containing pyridine rings, that is, 2.09 × 10^?1 S/cm at 150°C, which was higher than that of Nafion ? . Therefore, these films can be used at higher temperatures than that of Nafion ? .     

Grain-Boundary-Free Super-Proton Conduction of a Solution-Processed Prussian-Blue Nanoparticle Film

A porous crystal family has been explored as alternatives of Nafion films exhibiting super-proton conductivities of ≥10⁻² S cm⁻¹. Here, the proton-conduction natures of a solution-processed film of nanoparticles (NPs) have been studied and compared to those of a Nafion film. A mono-particle film of Prussian-blue NPs is spontaneously formed on a self-assembled monolayer substrate by a one-step solution process. A low-temperature heating process of the densely packed, pinhole-free mono-particle NP film enables a maximum 10⁵-fold enhancement of proton conductivity, reaching ca. 10⁻¹ S cm⁻¹. The apparent highest conductivity, compared to previously reported data of the porous crystal family, remains constant against humidity changes by an improved water-retention ability of the film. In our proposed mechanism, the high-performing solution-processed NP film suggests that heating leads to the self-restoration of hydrogen-bonding networks throughout their innumerable grain boundaries.     

Highly proton conducting proton‐exchange membranes based on fluorinated poly(arylene ether ketone)s with octasulfonated segments

A new bisphenol monomer containing a pair of electron‐rich tetra‐arylmethane units was designed and synthesized. Based on this monomer, along with commercial 4,4′‐(hexafluoroisopropylidene)diphenol A and 4,4′‐difluorobenzophenone, a series of novel poly(arylene ether ketone)s containing octasulfonated segments of varying molar percentage (x) (6F‐SPAEK‐x) were successfully synthesized by polycondensation reactions, followed by sulfonation. Tough, flexible, and transparent membranes, exhibiting excellent thermal stabilities and mechanical properties were obtained by casting. 6F‐SPAEK‐x samples exhibited appropriate water uptake and swelling ratios at moderate ion exchange capacities (IECs) and excellent proton conductivities. The highest proton conductivity (215 mS cm⁻¹) is observed for hydrated 6F‐SPAEK‐15 (IEC = 1.68 meq g⁻¹) at 100 °C, which is more than 1.5 times that of Nafion 117. Furthermore, the 6F‐SPAEK‐10 membrane exhibited comparable proton conductivity (102 mS cm⁻¹) to that of Nafion 117 at 80 °C, with a relatively low IEC value (1.26 meq g⁻¹). Even under 30% relative humidity, the 6F‐SPAEK‐20 membrane (2.06 meq g⁻¹) showed adequate conductivity (2.1 mS cm⁻¹) compared with Nafion 117 (3.4 mS cm⁻¹). The excellent comprehensive properties of these membranes are attributed to well‐defined nanophase‐separated structures promoted by strong polarity differences between highly ionized and fluorinated hydrophobic segments. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 25–37