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.     

Amperometric Tyrosinase Biosensor Based on Carbon Nanotube–Titania–Nafion Composite Film

A highly sensitive and stable amperometric tyrosinase biosensor has been developed based on multiwalled carbon nanotube (MWCNT) dispersed in mesoporous composite films of sol–gel‐derived titania and perfluorosulfonated ionomer (Nafion). Tyrosinase was immobilized within a thin film of MWCNT–titania–Nafion composite film coated on a glassy carbon electrode. Phenolic compounds were determined by the direct reduction of biocatalytically‐liberated quinone species at ?100 mV versus Ag/AgCl (3 M NaCl) without a mediator. The present tyrosinase biosensor showed good analytical performances in terms of response time, sensitivity, and stability compared to those obtained with other biosensors based on different sol–gel matrices. Due to the large pore size of the MWCNT–titania–Nafion composite, the present biosensor showed remarkably fast response time with less than 3 s. The present biosensor responds linearly to phenol from 1.0×10^?7 M to 5.0×10^?5 M with an excellent sensitivity of 417 mA/M and a detection limit of 9.5×10^?8 M (S/N=3). The enzyme electrode retained 89% of its initial activity after 2 weeks of storage in 50 mM phosphate buffer at pH 7.0.     

Amperometric phenol biosensor based on sol-gel silicate/Nafion composite film

An amperometric biosensor based on tyrosinase immobilized in silicate/Nafion composite film has been developed for the determination of phenolic compounds. The Nafion polymer in the composite was used not only to overcome the brittleness of the pure sol-gel-derived silicate film but also to increase the long-term stability of the biosensor. Tyrosinase was immobilized by a thin film of silicate/Nafion composite on a glassy carbon electrode. Phenolic compounds were determined by the direct reduction of biocatalytically-liberated quinone species at −200 mV versus Ag/AgCl (3 M NaCl). The process parameters for the fabrication of the enzyme electrode and various experimental variables such as pH and operating potential were explored for optimum analytical performance of the enzyme electrode. The biosensor can reach 95% of steady-state current in about 15 s. The sensitivities of the biosensor for catechol and phenol were 200 and 46 mA/M, respectively. A detection limit of 0.35 mM catechol was obtained with a signal-to-noise ratio of 3. The enzyme electrode retained 74% of its initial activity after 2 weeks of storage in 50 mM phosphate buffer at pH 7.     

丙烯酸水溶液聚合法制备PTFE/PAA/Nafion膜及其性能

采用廉价的多孔聚四氟乙烯(PTFE)膜作为基底, 用少量的Nafion与PTFE膜复合可制备低成本的质子膜. 但疏水性的PTFE膜与亲水性的Nafion膜结合性不佳. 基于此, 本文对疏水性的PTFE膜材料表面进行设计, 先采用丙烯酸对疏水性的PTFE膜表面进行亲水性改性, 再喷涂亲水性Nafion膜, 完成低成本PTFE/PAA/Nafion膜的制备. 实验结果表明, 改性前的PTFE膜材料水接触角为150°, 改性后的膜接触角变为55.6°, 亲水性大幅上升, 膜的机械强度和尺寸稳定性(断裂强度为25.2 MPa, 80 ℃下的溶胀率为11.9%)均优于Nafion117膜, 而 Nafion用量则节省了60%. PTFE/PAA/Nafion膜具有高质子导通率(80 ℃下达到131.9 mS/cm), 接近于Nafion117膜, 最大功率密度可以达到404.2 mW/cm².     

Tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence sensor based on carbon nantube dispersed in sol-gel-derived titania-Nafion composite films

A highly sensitive and stable tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) electrogenerated chemiluminescence (ECL) sensor was developed based on carbon nanotube (CNT) dispersed in mesoporous composite films of sol-gel titania and perfluorosulfonated ionomer (Nafion). Single-wall (SWCNT) and multi-wall carbon nanotubes (MWCNT) can be easily dispersed in the titania-Nafion composite solution. The hydrophobic CNT in the titania-Nafion composite films coated on a glassy carbon electrode certainly increased the amount of Ru(bpy)₃²⁺ immobilized in the ECL sensor by adsorption of Ru(bpy)₃²⁺ onto CNT surface, the electrocatalytic activity towards the oxidation of hydrophobic analytes, and the electronic conductivity of the composite films. Therefore, the present ECL sensor based on the CNT-titania-Nafion showed improved ECL sensitivity for tripropylamine (TPA) compared to the ECL sensors based on both titania-Nafion composite films without CNT and pure Nafion films. The present Ru(bpy)₃²⁺ ECL sensor based on the MWCNT-titania--Nafion composite gave a linear response (R² = 0.999) for TPA concentration from 50 nM to 1.0 mM with a remarkable detection limit (S/N = 3) of 10 nM while the ECL sensors based on titania-Nafion composite without MWCNT, pure Nafion films, and MWCNT-Nafion composite gave a detection limit of 0.1 μM, 1 μM, and 50 nM, respectively. The present ECL sensor showed outstanding long-term stability (no signal loss for 4 months).     

Pyropolymer-based Oxygen Electrode for Solid Polymer Electrolyte Systems

The activity of composite materials (acetylene black or ultrafinely divided dynamic diamond + Co-pyropolymer + Nafion solution) in the oxygen electroreduction in a 0.5 M H₂SO₄solution and when using a Nafion-117 film 200 m thick as a proton-conducting electrolyte is compared. It is established that the addition of Nafion in the active mass leads to a decrease in the electrocatalytic activity of the latter. The same composite catalyst (at an insignificant thickness of the active layer) in contact with a solid polymer electrode makes it possible to obtain current densities ten times those in a sulfuric acid solution. Possible reasons for these effects are discussed.     

Voltammetry determination of dopamine by the electrocatalytic response of an electrode modified by a polyaniline film with an inclusion of copper(II) tetrasulfophthalocyanine

A polyaniline composite film with an inclusion of copper(II) tetrasulfophthalocyanine, applied on a glassy-carbon electrode (GC) has demonstrated a mediatory activity in the oxidation of dopamine in acidic and neutral media. The conditions for the formation of a polymer film on the surface of a glassy-carbon electrode for registering the maximum electrocatalytic effect in the oxidation of dopamine are found. A method of voltammetric and amperometric detection of dopamine on the composite film electrode under static and flow conditions is proposed. The use of a polyaniline composite with an inclusion of copper(II) tetrasulfophthalocyanine, coated with a Nafion film, made possible the reduction of the detection limit for dopamine to 1 × 10^?8 M under static conditions and to 5.0 nmol under the conditions of flow-injection analysis.     

Electrochemical Characterization of Poly(N‐acetylaniline)/Nafion Composite Film in Neutral and Basic Aqueous Solutions

Electrochemical synthesis of poly(N‐acetylaniline) (PNAANI)/Nafion composite film was carried out by cyclic voltammetry (CV). Its surface morphology, which was evaluated by scanning electron microscopy (SEM), revealed that PNAANI was dispersed into the Nafion film uniformly. X‐ray photoelectron spectrum (XPS) of the composite film was also examined. The electroactivity of the composite film was high in neutral and basic solutions, and the stability of PNAANI/Nafion film in neutral and basic solutions was excellent.     

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.     

Electrochemical oxidation of p-nitrophenol using graphene-modified electrodes, and a comparison to the performance of MWNT-based electrodes

The electrochemical oxidation of p-nitrophenol (p-NP) has been studied comparatively on a graphene modified electrode and a multiwall carbon nanotube (MWNT) electrode by using cyclic and differential pulse voltammetry. The sensors were fabricated by modifying screen-printed electrodes with graphene and MWNT nanomaterials, respectively, both dispersed in Nafion polymer. p-NP is irreversibly oxidized at +0.9?V (vs. the Ag/AgCl) in solutions of pH 7. The height and potential of the peaks depend on pH in the range from 5 to 11. In acidic media, p-NP yields a well-defined oxidation peak at +0.96?V which gradually increases in height with the concentration of the analyte. In case of differential pulse voltammetry in sulfuric acid solution, the sensitivity is practically the same for both electrodes. The modified electrodes display an unusually wide linear response (from 10???M to 0.62?mM of p-NP), with a detection limit of 0.6???M in case of the graphene electrode, and of 1.3???M in case of the MWNT electrode.

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.     

Electrogenerated Chemiluminescence Ethanol Biosensor Based on Carbon Nanotube‐Titania‐Nafion Composite Film

Mesoporous titania‐Nafion composite doped with carbon nanotube (CNT) has been used for the immobilization of tris(2,2′‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) and alcohol dehydrogenase on an electrode surface to yield a highly sensitive and stable electrogenerated chemiluminescence (ECL) ethanol biosensor. The presence of CNT in the composite film increases not only the sensitivity of the ECL 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 1.0×10^?1 M with a detection limit of 5.0×10^?6 M (S/N=3). The present ECL ethanol biosensor exhibited higher ECL response compared to that obtained with the ECL biosensor based on the corresponding composite without CNT. The present CNT‐based ECL biosensor showed good long‐term stability with 75% of its initial activity retained after 2 weeks of storage in 50 mM phosphate buffer at pH 7.0.     

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.     

Application of a palladium hexacyanoferrate film-modified aluminum electrode to electrocatalytic oxidation of hydrazine.

A palladium hexacyanoferrate (PdHCF) film as an electrocatalytic material was obtained at an aluminum (Al) electrode by a simple electroless dipping method. The modified Al electrode demonstrated a well-behaved redox couple due to the redox reaction of the PdHCF film. The PdHCF film showed an excellent electrocatalytic activity toward the oxidation of hydrazine. The electrocatalytic oxidation of hydrazine was studied by cyclic voltammetry and rotating disk electrode voltammetry techniques. A calibration graph obtained for the hydrazine consisted of two segments (localized at concentration ranges 0.39-10 and 20-75 mM). The rate constant k and transfer coefficient alpha for the catalytic reaction and the diffusion coefficient of hydrazine in the solution D, were found to be 3.11 x 10(3) M(-1) s(-1), 0.52 and 8.03 x 10(-6) cm2 s(-1) respectively. The modified electrode was used to amperometric determination of hydrazine in photographic developer. The interference of ascorbic acid and thiosulfate were investigated and greatly reduced using a thin film of Nafion on the modified electrode. The modified electrode indicated reproducible behavior and a high level of stability during electrochemical experiments, making it particularly suitable for analytical purposes.     

Polycaprolactone and poly-β-cyclodextrin polymer blend: a Biopolymers composite film for drug release

Nowadays, biomedical films containing drug carriers are preferred over conventional ones, since the protection of the injury and the therapy is joined within a single device. In the current work, we prepared polycaprolactone (PCL) composite films with β-cyclodextrin (βCD) or its epichlorohydrin crosslinked polymer (βCDP) as ibuprofen (Ibu) drug carrier. The composite films were prepared at different PCL/additive ratios (2, 5, 10 and 20 wt%). ATR-FTIR spectroscopy and water contact angle (WCA) measurements indicated a scarce presence of the additives on the surface. Cross-section scanning electron micrographs showed the presence of aggregates corresponding to βCD and βCDP in the inner regions of the films. The incorporation of βCD and βCDP into the PCL films did not affect their thermal properties as was determined from differential scanning calorimetry (DSC). PCL-films with 10 wt% of the inclusion complexes Ibu@βCD and Ibu@βCDP were prepared and the release studies were performed. At pH?=?7.2, PCL-Ibu@βCDP composite film released 55% of Ibu within the first six hours; eight times the amount released by PCL-Ibu@βCD within the same time interval. A plausible mechanism for ibuprofen release is discussed based on the cross-section SEM micrographs of composite films.

     

Sandwich-type functionalized graphene sheet-sulfur nanocomposite for rechargeable lithium batteries

A functionalized graphene sheet-sulfur (FGSS) nanocomposite was synthesized as the cathode material for lithium-sulfur batteries. The structure has a layer of functionalized graphene sheets/stacks (FGS) and a layer of sulfur nanoparticles creating a three-dimensional sandwich-type architecture. This unique FGSS nanoscale layered composite has a high loading (70 wt%) of active material (S), a high tap density of ～0.92 g cm(-3), and a reversible capacity of ～505 mAh g(-1) (～464 mAh cm(-3)) at a current density of 1680 mA g(-1) (1C). When coated with a thin layer of cation exchange Nafion film, the migration of dissolved polysulfide anions from the FGSS nanocomposite was effectively reduced, leading to a good cycling stability of 75% capacity retention over 100 cycles. This sandwich-structured composite conceptually provides a new strategy for designing electrodes in energy storage applications.     

A polymer inclusion membrane based on the ionic liquid trihexyl(tetradecyl)phosphonium chloride and PVC for solid–liquid extraction of Zn(II) from hydrochloric acid solution

Abstract  

Extraction of Zn(II) from aqueous solution using polymer inclusion membranes based on poly(vinyl chloride) containing the phosphonium-based ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos^? IL 101) is described. Zn(II) could efficiently be extracted from 5 M hydrochloric acid solution with membranes containing 30 wt% Cyphos IL 101, whereas back-extraction was successfully achieved with 1 M sulfuric acid. Prepared membranes were evaluated in terms of stability in air as well as in terms of leaching of the ionic liquid from the membranes in aqueous solution.     

Electrochemiluminescence from tris(2,2′-bipyridyl)ruthenium(II)-graphene-Nafion modified electrode

An electrochemiluminescence (ECL) sensor based on Ru(bpy)₃²⁺-graphene-Nafion composite film was developed. The graphene sheet was produced by chemical conversion of graphite, and was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman spectroscopy. The introduction of conductive graphene into Nafion not only greatly facilitates the electron transfer of Ru(bpy)₃²⁺, but also dramatically improves the long-term stability of the sensor by inhibiting the migration of Ru(bpy)₃²⁺ into the electrochemically inactive hydrophobic region of Nafion. The ECL sensor gives a good linear range over 1 × 10⁻⁷ to 1 × 10⁻⁴ M with a detection limit of 50 nM towards the determination of tripropylamine (TPA), comparable to that obtained by Nafion-CNT. The ECL sensor keeps over 80% and 85% activity towards 0.1 mM TPA after being stored in air and in 0.1 M pH 7.5 phosphate buffer solution (PBS) for a month, respectively. The long-term stability of the modified electrode is better than electrodes modified with Nafion, Nafion-silica, Nafion-titania, or sol-gel films containing Ru(bpy)₃²⁺. Furthermore, the ECL sensor was successfully applied to the selective and sensitive determination of oxalate in urine samples.     

Direct electrochemistry of glucose oxidase on the hydroxyapatite/Nafion composite film modified electrode and its application for glucose biosensing

A novel glucose biosensor was constructed by immobilizing the glucose oxidase (GOD) on a hydroxyapatite (HAp)/Nafion composite film modified glassy carbon electrode (GCE) and applied to the highly selective and sensitive determination of glucose. With the cooperation of HAp and Nafion, the composite film played an important role in enhancing the stability and sensitivity of the biosensor. The results demonstrate that the GOD adsorbed onto the HAp/Nafion composite film exhibits a pair of well-defined nearly reversible redox peaks and fine catalysis to the oxidation of glucose companied with the consumption of dissolved oxygen. On the basis of the decrease of the reduction current of dissolved oxygen at the applied potential of −0.80 V (vs. SCE) upon the addition of glucose, the concentration of glucose could be detected sensitively and selectively. The decreased reduction current was linear with the concentration of glucose in the range of 0.12–2.16 mM. The detection limit and sensitivity were 0.02 mM (S/N = 3) and 6.75 mA·M⁻¹, respectively. All the results demonstrate that HAp/Nafion composite film provides a novel and efficient platform for the immobilization of enzymes and realizes the direct electrochemistry. The composite materials should have potential applications in the fabrication of third-generation biosensors.     

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.