Electrochemical Preparation of Poly(Malachite Green) Film Modified Nafion‐Coated Glassy Carbon Electrode and Its Electrocatalytic Behavior Towards NADH,Dopamine and Ascorbic Acid

Poly(malachite green) film modified Nafion‐coated glassy carbon electrodes have been prepared by potentiodynamic cycling in malachite green solution. The pH of polymerisation solution has only minor effect on film formation. Electrochemical quartz crystal microbalance (EQCM) was used to monitor the growth of the poly(malachite green) film. Cyclic voltammogram of the poly(malachite green) film shows a redox couple with well‐defined peaks. The redox response of the modified electrode was found to be depending on the pH of the contacting solution. The peak potentials were shifted to a less positive region with increasing pH and the dependence of the peak potential was found to be 56 mV per pH unit. The electrocatalytic behavior of poly(malachite green) film modified Nafion‐coated glassy carbon electrodes was tested towards oxidation of NADH, dopamine, and ascorbic acid. The oxidation of dopamine and ascorbic acid occurred at less positive potential on poly(malachite green) film compared to bare glassy carbon electrode. In the case of NADH, the overpotential was reduced substantially on modified electrode. Finally, the feasibility of utilizing poly(malachite green) film electrode in analytical estimation of ascorbic acid was demonstrated in flow injection analysis.     

Electrochemical Preparation of Brilliant‐Blue‐Modified Poly(diallyldimethylammonium Chloride) and Nafion‐Coated Glassy Carbon Electrodes and Their Electrocatalytic Behavior Towards Oxygen and L‐Cysteine

Brilliant blue FCF‐modified glassy carbon electrodes have been prepared by cycling the Nafion (or poly(diallyldimethylammonium chloride) (PDDAC)) coated electrodes repeatedly 15 cycles in brilliant blue FCF (BB FCF) dye solution. The BB FCF molecules are incorporated into Nafion coating by cycling the film‐covered electrode between +0.3 to 1.2 V (vs. Ag/AgCl) in pH 1.5 BB FCF solution while PDDAC‐coated electrode cycled between 0 to ?1.0 V (vs. Ag/AgCl) in pH 6.5 BB FCF solution to immobilize the dye. Electrostatic interaction between dye molecule and PDDAC was predominant in PDDAC coating whereas immobilization of dye in Nafion film attributed to the combined effect of electrostatic and hydrophobic interactions. The voltammetric features of BB FCF‐modified electrodes resemble that of surface‐confined redox couples. The peak potentials of BB FCF‐incorporated PDDAC‐coated electrode were shifted to more positive potential region with decreasing pH of contacting solution. BB FCF‐modified electrodes showed electrocatalytic activity towards reduction of oxygen and oxidation of L ‐cysteine with significant decease of overvoltage compared to unmodified electrode. The BB FCF‐modified Nafion‐coated electrode was tested for its analytical applications toward determination of L ‐cysteine. The linear range of calibration plot at BB FCF‐modified Nafion‐coated electrode is 10 to 100 μM, which coincides with L ‐cysteine levels in biological fluids. Sensitivity and detection limit of the electrode are 111 nA μM^?1 and 0.5 μM, respectively.     

A Highly Sensitive Electrochemical Impedance Spectroscopy Immunosensor for Determination of 1‐Pyrenebutyric Acid Based on the Bifunctionality of Nafion/Gold Nanoparticles Composite Electrode

A simple, highly sensitive and label‐free electrochemical impedance spectroscopy (EIS) immunosensor was developed using Nafion and gold nanoparticles (nano‐Au/Nafion) composites for the determination of 1‐pyrenebutyric acid (PBA). Under the optimal conditions, the amount of immobilized antibody was significantly improved on the nano‐Au/Nafion electrode due to the synergistic effect and biocompatibility of Nafion film and gold nanoparticles composites. The results showed that the sensitivity and stability of nano‐Au/Nafion composite electrode for PBA detection were much better than those of nano‐Au modified glassy carbon electrode (nano‐Au/GCE). The plot of increased electron transfer resistances (R_ets) against the logarithm of PBA concentration is linear over the range from 0.1 to 150 ng·mL^?1 with the detection limit of 0.03 ng·mL^?1. The selectivity and accuracy of the proposed EIS immunosensor were evaluated with satisfactory results.     

Electropreparation of Poly(benzophenone‐4) Film Modified Electrode and Its Electrocatalytic Behavior Towards Dopamine,Ascorbic Acid and Nitrite

The oxidation of benzophenone‐4 (2‐hydroxy‐4‐methoxybenzophenone‐5‐sulfonic acid) at glassy carbon electrode gives rise to stable redox active electropolymerized film during repetitive potential cycling between 0 to 1.3 V (Ag/AgCl). Cyclic voltammogram of poly(benzophenone‐4) film shows a redox couple with well‐defined peaks. The redox response of the modified electrode was found to be depending on the pH of the contacting solution. The peak potentials were shifted to a less positive region with increasing pH and the dependence of the peak potential was found to be 51 mV/pH. The electrocatalytic behavior of poly(benzophenone‐4) film modified electrode towards oxidation of dopamine, ascorbic acid and reduction of nitrite was investigated. The oxidation of dopamine and ascorbic acid occurred at less positive potential on poly(benzophenone‐4) film compared to bare glassy carbon electrode. For dopamine, the overpotential was reduced about 180 mV. Feasibility of utilizing poly(benzophenone‐4) film coated electrode in analytical estimation of dopamine, ascorbic acid and nitrite was also demonstrated.     

Amperometry of Heparin Polyion Using a Rotating Disk Electrode Coated with a Plasticized PVC Membrane

Electrochemical method of detection of heparin polyion was developed based on voltammetry of heparin on a rotating glassy carbon (GC) electrode coated with a plasticized PVC membrane. The membrane was deposited on the GC disk by spin‐coating technique using a mixture of solutions of PVC in tetrahydrofuran, and 1,1′‐dimethylferrocene (DMFc) and hexadecyltrimethylammonium tetrakis(4‐chlorophenyl)borate (HTMATPBCl) in o‐nitrophenyl octyl ether. UV/vis reflection spectrometry was used to evaluate the membrane thickness, which exhibits a linear correlation with the membrane resistance measured by impedance spectroscopy. It is shown that this electrode can be used for amperometric or coulometric detection of heparin in aqueous samples of medically relevant concentrations (1–10 U mL^?1), with a detection limit of 1.4 U mL^?1. Evidence is provided indicating that the current determining step is the reversible adsorption of the ion‐pair of heparin polyion with HTMA⁺ cation at the membrane/aqueous electrolyte interface, which is driven by oxidation of DMFc at the GC/membrane interface.     

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.     

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.     

Square‐Wave Voltammetric Detection of Dopamine at a Copper‐(3‐Mercaptopropyl) Trimethoxy Silane Complex Modified Electrode

Square‐wave voltammetric detection of dopamine was studied at a copper (Cu)‐(3‐mercaptopropyl) trimethoxy silane (MPS)‐complex modified electrode (Cu‐MPS). The modification of the electrode was based on the attachment of MPS onto an electrochemically activated glassy carbon electrode (GCE) by the interaction between methoxy silane groups of MPS and surface hydroxyl groups and followed by the complexation of copper with the thiol groups of MPS. The surface of the modified electrode was further coated by a thin layer of Nafion film. The surface of the Nafion coated MPS‐Cu complex modified electrode (Nafion/Cu‐MPS) was characterized using cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM), scanning electron microscope (SEM), X‐ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT‐IR) spectrometry. The modified electrode exhibited an excellent electrocatalytic activity towards the oxidation of dopamine, which was oxidized at a reduced potential of +0.35 V (vs. Ag/AgCl) at a wider pH range. Various experimental parameters, such as the amount of copper, the pH, and the temperature were optimized. A linear calibration plot was obtained in the concentration range between 8.0×10^?8 M and 5.0×10^?6 M and the detection limit was determined to be 5.0×10^?8 M. The other common biological compounds including ascorbic acid did not interfere and the modified electrode showed an excellent specificity to the detection of dopamine. The Nafion/Cu‐MPS modified electrode can be used for about 2 months without any significant loss in sensitivity.     

Electrochemical and electrocatalytic behaviors of Safranin O/Nafion film deposited on the glassy carbon electrode

The glassy carbon (GC) electrode modified with Nafion and Safranin O (SFO) was prepared and its electrochemical properties were investigated. The SFO molecules were strongly and irreversibly adsorbed on the Nafion — modified GC surface. The electrochemical behavior and mechanism for interactions of the SFO molecules with the Nafion film were investigated through cyclic voltammetric method. The electrocatalytic reduction of nitric oxide was performed at this modified electrode by cyclic voltammetric and hydrodynamic amperometric techniques. The Nafion membrane played a duel role as a matrix for the SFO immobilization and also helped to partition the nitric oxide from the solution phase. The diffusion coefficient of NO at the SFO/Nafion/GC modified electrode was calculated using chronoamperometry. The dependence of response currents on the concentration of NO was examined and was linear in the range of 0.05–1.9 mM of NO.     

Electrochemical behavior of horseradish peroxidase on WS2 nanosheet‐modified electrode and electrocatalytic investigation

In this paper, a WS₂ nanosheet was modified on the surface of a carbon ionic liquid electrode (CILE), and horseradish peroxidase (HRP) was further fixed on the electrode with a Nafion film. Direct electrochemistry and bioelectrocatalysis of HRP incorporated on the modified electrode were investigated in detail. On Nafion/HRP/WS₂/CILE, a pair of well‐defined quasi‐reversible redox peaks appeared on the cyclic voltammogram, indicating that the presence of the WS₂ nanosheet on the electrode surface could provide a specific interface with large surface area for HRP and its direct electron transfer rate was greatly enhanced. The formal potential (E⁰) obtained was –0.179 V, which was the typical feature of heme Fe(III)/Fe(II) in HRP. The electron transfer coefficient (α) and the heterogeneous electron transfer rate constant (k_s) of HRP were calculated as 0.44 and 1.01 s^–1, respectively. This HRP‐modified electrode showed excellent electrocatalytic activity for the reduction of trichloroacetic acid and NaNO₂ with a wide linear range and low detection limit. Real samples were detected by this proposed method, indicating the successful fabrication of a new third‐generation electrochemical enzyme sensor utilizing the WS₂ nanosheet.     

Lifetime Improvement of Glucose Biosensor by Epoxy‐Enhanced PVC Membrane

A new approach using epoxy resin to enhance the durability and adhesion of a diffusion‐limiting membrane in amperometric biosensors is described. The polymer membrane was mainly composed of commercially available fast epoxy adhesive ATACS 5104, poly(vinyl chloride) (PVC) and plasticizers such as isopropyl myristate (IMP) and Aliquat 336 (AL). It can be readily deposited on various substrates by using coating and other thin film fabrication methods. The effect of epoxy resin in the membrane composition was investigated using a coil‐type glucose biosensor containing extra enzyme. The ideal membrane was found to include approximately 1/3 epoxy resin, 1/3 plasticizer and 1/3 PVC. Such a membrane was verified to be porous and permeable to small molecules like glucose and can tightly adhere to other beneath layers such as a Nafion membrane, which serves as the interference‐eliminating layer. These epoxy‐based glucose biosensors showed excellent electrochemical response properties including a long lifetime and can be used for microanalysis of solutions and biological fluids. With an additional PU outermost layer, the present glucose biosensors can potentially be used for in vivo measurements.     

电聚合烟酰胺制备电化学传感器：同时测定多巴胺、尿酸和抗坏血酸

用循环伏安法（CV）选择不同电位区间来电聚合烟酰胺（NA）得到了两种聚合物膜修饰电极：poly-niacinamide/GCE (poly-NA/GCE)和poly- nicotinic acid /GCE (poly-NC/GCE)。这两电极都具有显著电化学催化作用,能明显地降低多巴胺（DA）、尿酸（UA）和抗坏血酸(AA)的氧化过电位,并在混合溶液中使这些物质的氧化峰电位距离足够大,可进行三物质的同时测定。poly-NC/GCE的电催化性能更好一些,用差分脉冲伏安法（DPV）测定抗坏血酸,线性范围为75–3000 µmol L-1,电流灵敏度为5.6 mA•L•mol-1;测定多巴胺,线性范围为0.37 – 16 µmol L-1,电流灵敏度为1140 mA•L•mol-1; 测定尿酸,线性范围为0.74 – 230 µmol L-1,电流灵敏度为102 mA•L•mol-1。该电极具有很高的灵敏度、选择性和抗污染能力。     

Nafion修饰碳纤维微电极在抗坏血酸共存下选择性测定去甲肾上腺素

制备了碳纤维微电极,将洁净的碳纤维微电极浸入Nafion溶液中,采用电沉积的方法制得Nafion修饰碳纤维微电极。采用循环伏安法(CV)、差分脉冲伏安法(DPV)研究了去甲肾上腺素(NE)和抗坏血酸(AA)在电极上的电化学行为。结果表明:在最优条件下制备的Nafion修饰电极能完全屏蔽AA的电化学响应,而对NE仍表现出良好的电化学响应。修饰电极能在1.0 mmol/L AA的共存下选择性地测定NE,采用DPV进行检测,NE的氧化峰电流与其浓度在1.0×10~(-6)~1.0×10~(-4)mol/L范围内呈良好的线性关系,相关系数(r~2)为0.991 2,检出限(S/N=3)为8.6×10~(-7)mol/L。利用该方法测定了模拟样品中NE的含量,平均加标回收率为101.6%。该电极的重现性和稳定性良好,且具有良好的灵敏度和选择性,有望用于复杂生物环境中NE浓度的检测。     

Detection of Uric Acid in the Presence of Dopamine and High Concentration of Ascorbic Acid Using PDDA Modified Graphite Electrode

The properties of graphite electrode (Gr) modified with poly(diallyl dimethyl ammonium chloride) (PDDA) for the detection of uric acid (UA) in the presence of dopamine (DA) and high concentration of ascorbic acid (AA) have been investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The polymer modified graphite electrode was prepared by a very simple method just by immersing the graphite electrode in PDDA solution for 20 minutes. The PDDA/Gr modified electrode displayed excellent electrocatalytic activity towards the oxidation of UA, DA and AA compared to that at the bare graphite electrode. The electrochemical oxidation signals of UA, DA and AA are well resolved into three distinct peaks with peak potential separations of 220 mV, 168 mV and 387 mV between AA‐DA, DA‐UA and AA‐UA respectively in cyclic voltammetry studies and the corresponding peak potential separations are 230 mV, 130 mV and 354 mV respectively in differential pulse voltammetry. The lowest detection limits obtained for UA, DA and AA were 1×10^?7 M, 2×10^?7 M and 800×10^?9 M respectively. The PDDA/Gr electrode efficiently eliminated the interference of DA and a high concentration of AA in the determination of UA with good selectivity, sensitivity and reproducibility. The modified electrode was also successfully applied for simultaneous determination of UA, DA and AA in their ternary mixture.     

A Mediator‐Free Bienzyme Amperometric Biosensor Based on Horseradish Peroxidase and Glucose Oxidase Immobilized on Carbon Nanotube Modified Electrode

Multiwalled carbon nanotube (CNT) modified glassy carbon electrode immobilized with horseradish peroxidase (HRP) in Nafion coating showed direct electron transfer between HRP enzyme and the CNT‐modified electrode. A mediator‐free bienzyme glucose biosensor based on horseradish peroxidase and glucose oxidase was constructed. The bienzyme biosensor exhibited a high sensitivity for glucose detection at zero applied potential.     

Fabrication of a Nanobiocomposite Film Containing Heme Proteins and Carbon Nanotubes on a Choline Modified Glassy Carbon Electrode: Direct Electrochemistry and Electrochemical Catalysis

A nanocomposite electrochemical sensing film is assembled on choline (Ch) modified glassy carbon electrode (GCE), which contains multiwalled carbon nanotubes (MWNTs), Nafion cation exchanger, and myoglobin (Mb) or hemoglobin (Hb). The MWNTs provide a 3D porous and conductive network for the enzyme immobilization and Nafion acts as polymeric binder to give cast thin films. Both MWNTs and Nafion provide negative functionalities to bind to the positively charged redox proteins and to attach at the positively charged Ch modified layer, and drive the formation of homogeneous and stable nanocomposite film, the MWNT‐Nafion‐Mb. The nanocomposite film was characterized by field emission scanning electron microscope (FE‐SEM). The Mb in the nanocomposite film showed a pair of well‐defined and nearly reversible cyclic voltammetric peaks at about ?0.32 V vs. SCE at pH 7.0 solution for the heme Fe(III)/Fe(II) redox couple. The immobilized heme proteins can display the features of peroxidase in electrocatalytic reductions of oxygen, hydrogen peroxide, nitric oxide, trichloroacetic acid (TCA), and bromate.     

Boron Nitride Nanosheet Modified Electrode: Preparation and Application to Direct Electrochemistry of Myoglobin

An ionic liquid modified carbon paste electrode (CILE) was prepared with 1‐hexylpyridine hexafluorophosphate (HPPF₆) and used as a substrate electrode. Then hexagonal boron nitride (BN) nanosheet, myoglobin (Mb) and Nafion were fixed on the electrode surface by coating method to get a new‐style chemically modified electrode (Nafion/Mb/BN/CILE). The morphology and crystal phase of BN nanosheet were characterized by SEM, TEM and XRD. UV‐Vis and FT‐IR results showed that Mb retained its original conformation in the composite modified film. In phosphate buffer solutions (PBS) with pH 3.0, cyclic voltammetry (CV) was performed to investigate the direct electrochemical behaviour of Mb. A pair of quasi‐reversible redox reaction peaks was obtained on the CV curve, proving that BN nanosheet had good biocompatibility and could accelerate electron transfer between Mb and electrode surface. Electrocatalytic reduction of trichloroacetic acid (TCA) was investigated, which was further applied to TCA detection. The catalytic reduction peak current at ?0.355 V depended linearly on the TCA concentration in the range of 0.2～30.0 mmol/L with the equation of Ipc (μA)=6.340 C (mmol/L)+0.305 (r=0.998), and the detection limit was 0.05 mmol/L (3 σ).     

Sulfonated poly(ether ether ketone)/poly(vinylpyrrolidone) acid–base polymer blends for direct methanol fuel cell application

Acid–base polymer blends for polymer electrolyte membranes have been prepared by blending sulfonated poly(ether ether ketone) (SPEEK) with poly(vinylpyrrolidone) (PVP) to reduce methanol uptake and to decrease methanol permeability while maintaining high proton conductivity. The acid‐base interaction occurring on the sulfonic acid group and on the tertiary amide group was characterized by FTIR and DMA. As the composition of PVP lowered than 20 wt % in the blends, the acid–base interaction causes great reduction on methanol uptake and the methanol permeability; however, the proton conductivity is still high. In this work, membrane–electrode assemblies (MEAs) have been prepared for direct methanol fuel cell (DMFC) from both blend membrane and Nafion 117. DMFC single cell performance was also evaluated. Results confirmed that SPEEK (with the degree of sulfonation (DS) = 69%) blended with PVP (M_n = 1,300,000) with a ratio of 80/20 (w/w) exhibits higher open‐circuit voltages (OCV) and lower polarization loss than those of Nafion 117. These acid–base blends will be suitable for DMFC application. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 565–572, 2006     

Simultaneous Voltammetric Determination of Uric Acid and Ascorbic Acid Using a Carbon‐Paste Electrode Modified with Multi‐Walled Carbon Nanotubes/Nafion and Cobalt(II)nitrosalophen

A composition of multiwalled carbon nanotube (MWCNT), Nafion and cobalt(II)‐5‐nitrosalophen (CoNSal) is applied for the modification of carbon‐paste electrode (CPE). The pretreated MWCNT is well dispersed in the alcoholic solution of Nafion under the ultrasonic agitation, and the resulted suspension is used as modifier (with 10% w/w) in the matrix of the paste electrode. The prepared electrode further modified by addition of 3 wt% of CoNSal. The resulted modified electrode is used as a sensitive voltammetric sensor for simultaneous determination of uric acid (UA) and ascorbic acid (AA). The electrode showed efficient electrocatalytic activity in lowering the anodic overpotentials and enhancement of the anodic currents. This electrode is able to completely resolve the voltammetric response of UA and AA. The effects of potential sweep rate and pH of the buffer solution on the response of the electrode, toward UA and AA, and the peak resolution is thoroughly investigated by cyclic and differential pulse voltammetry (CV and DPV). The best peak resolution for these compounds using the modified electrode is obtained in solutions with pH 4. The ΔE_p for UA and AA in these methods is about 315 mV, which is considerably better than previous reports for these compounds. A linear dynamic range of 1×10^?7 to 1×10^?4 M with a detection limit of 6×10^?8 M is resulted for UA in buffered solutions with pH 4.0. The voltammetric response characteristics for AA are obtained as, the linear range of 5×10^?7 to 1×10^?4 M with the detection limit of 1×10^?7 M. The voltammetric detection system was very stable and the reproducibility of the electrode response, based on the six measurements during one month, was less than 3.5% for the slope of the calibration curves of UA and AA. The prepared modified electrode is successfully applied for the determination of AA and UA in mixture samples and reasonable accuracies are resulted.     

A Highly Sensitive and Selective Multiwall Carbon Nanotubes/Nafion/Au Microarrays Electrode for Dopamine Determination

This work presents the fabrication of Nafion (Nf) or Nafion/Multiwalled Carbon Nanotubes (Nf/MWCNTs) modified gold microarray (Au‐µA) and macro‐(Au‐M)electrode biosensors. The surface morphologies of the above electrodes were examined using SEM. The catalytic properties of the above electrodes towards dopamine were tested using square wave voltammetric technique. The Nf/MWCNT/Au‐µA electrode exhibited a wide range (0.1–1000 nM) of linearity among the other electrodes. The LOD of Nf/MWCNT/Au‐µA electrode was 50 pM for dopamine in the presence of 5000 µM ascorbic acid. Therefore, the Nf/MWCNT/Au‐µA biosensor was applied for the determination of dopamine in human serum.