Characterization of an EDTA bonded conducting polymer modified electrode: its application for the simultaneous determination of heavy metal ions

An EDTA bonded conducting polymer modified electrode (EDTA-CPME) was fabricated by polymerization of 3',4'-diamino-2,2';5',2'-terthiophene monomer on a GCE, followed by the reaction with EDTA in the presence of catalyst. The surface of the resulting modified electrode was characterized with EQCM, ESCA, SEM, Auger electron spectroscopy, scanning Auger microscopy, and electrochemical methods. The amounts of polymer and EDTA attached on the polymer film were determined. Simple immersing of the EDTA-CPME into a sample solution led to the chemical deposition through the complexation with Pb2+, Cu2+, and Hg2+ ions, simultaniously. Various experimental parameters that affect the simultaneous analysis of the metal ions, e.g., EDTA amount, pH, deposition time, and deposition temperature, were optimized. Calibration plots for the EDTA-CPME with square wave voltammetry were obtained in the concentration range between 5.0 x 10(-10) and 1.0 x 10(-7) M for Cu(II) and between 7.5 x 10(-10) and 1.0 x 10(-7) M for Pb(II) and Hg(II). The detection limits for Pb(II), Cu(II), and Hg(II) ions were determined to be about 6.0 x 10(-10), 2.0 x 10(-10), and 5.0 x 10(-10) M, respectively. Interference effects from other metal ions were studied at various pHs and it was found that there was little or no effect on the simultaneous determination. The stability of the EDTA-CPME was remarkably improved by coating the surface with the Nafion film, and the electrode can be used for more than one month. Analytical availability of the EDTA-CPME was demonstrated by the application for the certified standard urine reference material and tap water.     

Fabrication of a near-infrared sensor using a polyaniline conducting polymer thin film

Near infrared (NIR) photo-responsive polyaniline-based conducting thin films are developed for sensor application. Upon NIR illumination (2.43 W/cm²), the electrical conductance of the polyaniline thin films was enhanced 5.9% and the response time was 20 s. NIR sensing performance of polyaniline conducting polymer thin film is comparable with that of bolometric carbon nanotube (CNT) network devices with the merits of polymers over CNTs such as processability, productivity and economy.     

Lipid-bonded conducting polymer layers for a model biomembrane: application to superoxide biosensors

Model biomembranes composed of poly-DATT/DGS/POPA and poly-DATT/DGS/CL were separately prepared on gold electrodes. A monolayer of 1,2-dioleoyl-sn-glycero-3-succinate (DGS) was covalently bonded onto electrochemically grown poly-(3,4-diamiono-2,2:5,2-terthiophene) (DATT) layers (thickness of approximately 300 nm; particle size of approximately 50 to 70 nm). The numbers of unit molecules of the poly-DATT layer and of the DGS immobilized onto the poly-DATT layers were 1.53 x 10(-7) and 1.56 x 10(-9) mol cm(-2), respectively, using a quartz crystal microbalance technique. The lipid bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate (POPA) and cardiolipin (CL) were formed onto the poly-DATT/DGS layer using the Langmuir-Blodgett technique. The surface characterizations of each step were investigated by SEM, AFM, and XPS analyses. Cytochrome c (cyt c) was immobilized onto these model biomembranes through the charge interaction between the positive charges of cyt c and the negative charges of phosphate groups in CL or POPA lipids. At the POPA- and CL-modified biomembranes, the formal potentials of the redox couple of the immobilized cyt c were 0.22 and 0.23 V (vs Ag/AgCl), respectively. The redox reaction of the immobilized cyt c at the POPA- and CL-modified biomembranes was quasireversible, and the electron-transfer rate constants were 0.121 s(-1) and 0.133 s(-1), respectively. The applicability of these cyt c immobilized bioimitation membranes as the biosensors was tested for the determination of superoxide.     

Direct electrochemistry and electrocatalytic activity of cytochrome c covalently immobilized on a boron-doped nanocrystalline diamond electrode

Cytochrome c (Cyt c) was covalently immobilized on a boron-doped nanocrystalline diamond (BDND) electrode via surface functionalization with undecylenic acid methyl ester and subsequent removal of the protecting ester groups to produce a carboxyl-terminated surface. Cyt c-modified BDND electrode exhibited a pair of quasi-reversible and well-defined redox peaks with a formal potential (E(0)) of 0.061 V (vs Ag/AgCl) in 0.1 M phosphate buffer solution (pH 7.0) and a surface-controlled process with a high electron transfer constant (ks) of 5.2 +/- 0.6 s(-1). The electrochemical properties of as-deposited and Cyt c-modified boron-doped microcrystalline diamond (BDMD) electrodes were also studied for comparison. Investigation of the electrocatalytic activity of the Cyt c-modified BDND electrode toward hydrogen peroxide (H2O2) revealed a rapid amperometric response (5 s). The linear range of response to H2O2 concentration was from 1 to 450 microM, and the detection limit was 0.7 microM at a signal-to-noise ratio of 3. The stability of the Cyt c-modified BDND electrode, in comparison with that of the BDMD and glassy carbon counterpart electrodes, was also evaluated.     

Direct electrochemistry and electrocatalysis of myoglobin immobilized on zirconia/multi-walled carbon nanotube nanocomposite

Zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) nanocomposite was prepared by hydrothermal treatment of MWCNTs in ZrOCl₂·8H₂O aqueous solution. The morphology and structure of the synthesized ZrO₂/MWCNT nanocomposite were characterized by transmission electron microscopy and X-ray diffraction analysis. It was found that ZrO₂ nanoparticles homogeneously distributed on the sidewall of MWCNTs. Myoglobin (Mb), as a model protein to investigate the nanocomposite, was immobilized on ZrO₂/MWCNT nanocomposite. Ultraviolet–visible spectroscopy and electrochemical measurements showed that the nanocomposite could retain the bioactivity of the immobilized Mb to a large extent. The Mb immobilized in the composite showed excellent direct electrochemistry and electrocatalytic activity to the reduction of hydrogen peroxide (H₂O₂). The linear response range of the biosensor to H₂O₂ concentration was from 1.0 to 116.0 μM with the limit of detection of 0.53 μM (S/N = 3). The ZrO₂/MWCNT nanocomposite provided a good biocompatible matrix for protein immobilization and biosensors preparation.     

Introduction of gold nanoparticles into myoglobin-Nafion film for direct electrochemistry application

An effective myoglobin-Nafion film is prepared by introducing gold nanoparticles in through a simple procedure by ion-exchange combined with electrochemical reduction. Gold nanoparticles are highly dispersed in myoglobin-Nafion film with an average size of 2.3 +/- 0.2 nm. The electrochemical behavior of myoglobin entrapped in the film has been carefully investigated with cyclic voltammetry. The results show that the introduction of gold nanoparticles into myoglobin-Nafion film makes the direct electron transfer of myoglobin efficient. A pair of well-defined redox peaks for myoglobin heme Fe(II)/Fe(III) is observed with a formal potential of -0.150 V in 0.1 M phosphate buffer (pH 7.0). The electrochemical parameters of myoglobin in the composite film are further calculated with the results of the electron-transfer rate constant (k(s)) as 0.93 s(-1) and the charge transfer coefficient (alpha) as 0.69. The experimental results also demonstrate that the immobilized myoglobin retains its electrocatalytic activity for the reduction of hydrogen peroxide and the catalytic reduction peak of myoglobin appear in a linear relationship with H2O2 concentration in the range of 10.0-235.0 microM with correlation coefficient of 0.9970. Thus fabricated Au/Mb/Nafion electrode should give a new approach for developing redox protein or enzyme-based biosensors.     

微过氧化物酶-11在碳纳米管/壳聚糖修饰电极上的直接电化学及电催化(英文)

采用一步法于室温下有选择性地将小管径的单壁碳纳米管(SWCNTs)分散于生物相容性的聚合物--壳聚糖的水溶液中,并将其滴涂于玻碳电极表面,制备出微过氧化物酶-11(MP-11)修饰电极.循环伏安结果表明SWCNq、促进了MP-11在电极表面的直接电子传递,在pH=7.2的磷酸缓冲溶液中,MP-11的式电位为-0.36 V(vs.SCE),MP-11在电极表面的直接电子转移表观速率常数和覆盖度分别为78 s-1和8.76×10-10mol·cm-2.进一步的研究结果显示,固定在SWCNT表面的MP-11能保持其对氧气和过氧化氢还原的生物电催化活性,适合用作生物燃料电池的阴极和过氧化氢传感器.氧气在该修饰电极上的还原经历一个四电子过程;该过氧化氢生物传感器对过氧化氢还原的检测具有响应灵敏度高(响应时间小于4 S),检测线性范围为2.5×10-6～7.0×10-3vM,检测限为0.8 μM,相应的米氏常数和检测灵敏度分别为1.0 mM and 22.4μA/mM.     

Direct sub-micrometer patterning of nanostructured conducting polymer films via a low-energy infrared laser

Despite the many attractive properties of conjugated polymers, their practical applications are often limited by the lack of a simple, scalable, and nondisruptive patterning method. Here, a direct, scalable, high-resolution patterning technique for conducting polymers is demonstrated that does not involve photoresists, masks, or postprocessing treatment. Complex, well-defined patterns down to sub-micrometer scales can be created from nanofibrous films of a wide variety of conducting polymers by photothermally welding the nanofibers using a low-energy infrared laser. The welding depth, structural robustness, and optical properties of the films are readily controlled. In addition, the electrical properties such as conductivity can be precisely tuned over a 7-order of magnitude range, while maintaining the characteristic tunable electronic properties in the nonwelded polyaniline regions.     

Immobilization of functional oxide nanoparticles on silicon surfaces via Si-C bonded polymer brushes

A method for immobilizing and mediating the spatial distribution of functional oxide (such as SiO2 and Fe3O4) nanoparticles (NPs) on (100)-oriented single crystal silicon surface, via Si-C bonded poly(3-(trimethoxysilyl)propyl methacrylate) (P(TMSPM)) brushes from surface-initiated atom transfer radical polymerization (ATRP) of (3-(trimethoxysilyl)propyl methacrylate) (TMSPM), was described. The ATRP initiator was covalently immobilized via UV-induced hydrosilylation of 4-vinylbenzyl chloride (VBC) with the hydrogen-terminated Si(100) surface (Si-H surface). The surface-immobilized Fe3O4 NPs retained their superparamagnetic characteristics and their magnetization intensity could be mediated by adjusting the thickness of the P(TMSPM) brushes.     

Fabrication of conducting polymer micro/nanostructures coated with Au nanoparticles for electrochemical sensors

Polypyrrole (PPy) micro/nanostructures coated with Au nanoparticles were prepared by electropolymerization and electro-deposition. Two types of PPy structures, micro-embossed and nanowire forest, were synthesized on patterned gold electrodes using different aqueous solutions, and Au nanoparticles were coated onto the PPy micro/nanostructure surface. The size of the Au nanoparticles ranged from 10 to 100 nm, and the maximum density of the nanoparticles was 73 particles/microm2. The small size and high density of the Au nanoparticles were achieved by optimizing the deposition time and chloroauric acid (HAuCl4) concentration. Cyclic voltammograms of ferrocyanide oxidation showed that the PPy micro/nanostructures coated with Au nanoparticles exhibit good electrochemical activity. These high-performance electrodes can be used in electrochemical sensors because the Au nanoparticles enhance electron transfer and provide a binding site for biomarker molecules, such as DNA, protein, and aptamers.     

Preparation of nanocomposite for optical application using ZnTe nanoparticles and a zero-birefringence polymer

Surface-modified ZnTe nanoparticles were mixed in a zero-birefringence polymer matrix. Transmission electron microscopy images revealed that aggregates of ZnTe nanoparticles with a diameter of ∼20 nm were uniformly dispersed in the polymer. The transmittance of ZnTe nanocomposites rapidly decreased at wavelengths shorter than the critical wavelength corresponding to the band gap of ZnTe nanoparticles, an effect which became significant as the volume fraction of particles increased. In this way, the optical characteristic of ZnTe nanoparticles was added to the polymer. The intrinsic zero-birefringence was confirmed in the heat-drawn ZnTe nanocomposites. As the ZnTe nanocomposites were left in air, a lowering of transmittance was observed. This was due to the oxidation of Zn and the resultant deposition of Te in the ZnTe nanocomposite, as the light absorption of Te is significant. The formation of oxygen non-permeable SiO₂ films onto the ZnTe nanocomposite by the sol-gel method was useful in preventing oxidation so that the decrement of transmittance decreased from 47.2% to 14.9% at 530 nm near the ZnTe band gap.     

Electrode biomaterials based on immobilized laccase. Application for enzymatic reduction of dioxygen

Three different methods of immobilization of the laccase enzyme have been studied by measuring the enzyme activity of the bioelectrode and its catalytic efficiency for dioxygen reduction in the presence of the 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) as a redox mediator. One approach has consisted in laccase entrapment in polypyrrole matrix electrogenerated on the electrode surface. The two other approaches have concerned the grafting of laccase on an original aminopolypyrrole film and the complexation of laccase with avidin and biotin reagents. The laccase activity and the catalytic current of dioxygen reduction have demonstrated the efficiency of covalent grafting to aminopolypyrrole film. The polymer thickness was a key parameter of the catalytic efficiency and stability of this type of biocathode.     

Low-temperature synthesis of ZnO nanoparticles for inverted polymer solar cell application

Zinc oxide (ZnO) nanoparticles were synthesized by a simple wet chemical method at low temperature. Morphologies, crystalline structure, and optical transmission of ZnO nanoparticles were investigated. The results showed that the average diameter of as-synthesized ZnO nanoparticles was about 4.9 nm, the nanoparticles were wurtzite-structured (hexagonal) ZnO and had optical band gap of 3.28 eV. Very high optical transmission (>80 %) in visible light region of ZnO nanoparticulate thin films was achieved. Furthermore, an inverted polymer solar cell consisted of ZnO nanoparticles and polymer were fabricated. The device exhibited an open circuit voltage (V_oc) of 0.50 V, a short circuit current density (J_sc) of 1.76 mA/cm², a fill-factor of 38 %, and a power conversion efficiency of 0.42 %.     

DNA electrochemical sensor based on conducting polymer: dependence of the "signal-on" detection on the probe sequence localization

We show in this work that it is possible to make selective direct electrochemical hybridization detection of a target strand onto a probe strand immobilized on a conducting polymer modified with a quinone group, which presents cation-exchange properties. This leads to a "signal-on"detection, a unique behavior in comparison to similar systems described in the literature. It is shown that this system is efficient for various probe and target lengths (10-30 bp) and can discriminate a single mismatch. To go further in comprehension of the detection mechanism, a systematic study of the electrochemical response versus the probe sequence localization onto the immobilized strand is performed. For example, a 30-bp target strand is divided into three shorter 10-bp sequences (A-C, respectively), and we investigate the successive hybridization of these 1/3 strands onto the 30-bp probe strand. It is shown that one probe strand can be used to address several shorter targets.     

SPR sensor chip for detection of small molecules using molecularly imprinted polymer with embedded gold nanoparticles

Molecularly imprinted polymer gel with embedded gold nanoparticle was prepared on a gold substrate of a chip for a surface plasmon resonance (SPR) sensor for fabricating an SPR sensor sensitive to a low molecular weight analyte. The sensing is based on swelling of the imprinted polymer gel that is triggered by an analyte binding event within the polymer gel. The swelling causes greater distance between the gold nanoparticles and substrate, shifting a dip of an SPR curve to a higher SPR angle. The polymer synthesis was conducted by radical polymerization of a mixture of acrylic acid, N-isopropylacrylamide, N,N'-methylenebisacrylamide, and gold nanoparticles in the presence of dopamine as model template species on a sensor chip coated with allyl mercaptan. The modified sensor chip showed an increasing SPR angle in response to dopamine concentration, which agrees with the expected sensing mechanism. Furthermore, the gold nanoparticles were shown to be effective for enhancing the signal intensity (the change of SPR angle) by comparison with a sensor chip immobilizing no gold nanoparticles. The analyte binding process and the consequent swelling appeared to be reversible, allowing one the repeated use of the presented sensor chip.     

Particle size effects on the mechanical properties of a polymer bonded explosive

Two RDX/HTPB polymer bonded explosives (PBXs), with different explosive particle size, were studied in a Hopkinson bar system at three different temperatures. Three temperatures were chosen, two above, and one below, the glass transition temperature of the binder material. The PBX consisted of cyclotrimethylene trinitramine (RDX) crystals in a hydroxyl-terminated-polybutadiene (HTPB) binder. Overall the larger particle sized material was weaker, and exhibited a more distinct yield point than the finer sized material. Both materials showed temperature sensitivity, the effect being greater in the material with the smaller particles.     

Silica chemically bonded N-propyl kriptofix 21 and 22 with immobilized palladium nanoparticles for solid phase extraction and preconcentration of some metal ions

Silica gel chemically bonded N-propyl kriptofix 21 (SBNPK 21) and N-propyl kriptofix 22 (SBNPK 22) and subsequently immobilized with palladium nanoparticles (PNP-SBNPK 21 and PNP-SBNPK 22) to produce two new complexing lipophilic materials. Then these novel sorbents were applied for the enrichment of some metal ions and their subsequent determination by flame atomic absorption spectroscopy (FAAS). The influences of the variables including pH, amount of solid phase, sample flow rate, eluent conditions and sample volume on the metal ion recoveries were investigated. The detection limit of proposed method was in the interval 2.1–2.3 and 1.7–2.8 ng mL^? 1 for PNP-SBNPK 21 and PNP-SBNPK 22 respectively, while the preconcentration factor was 80 for two sorbents. The relative standard deviations of recoveries were between 1.23–1.31 and 1.28–1.49 for PNP-SBNPK 21 and PNP-SBNPK 22 respectively. The method has high sorption-preconcentration efficiency even in the presence of various interfering ions. Due to the reasonable selectivity of proposed method, the relative standard deviation of recoveries of all understudied metal ions in some complicated matrices was less than 3.0%.     

Effect of ionic liquid dispersion on performance of a conducting polymer based Schottky diode

The effect of ionic liquid (IL) dispersion on the performance of Schottky diode fabricated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been investigated. Two kinds of ILs including 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6, hydrophobic IL) and 1-butyl-3-methylimidazolium chloride (BMICL, hydrophilic IL) were dispersed to the PEDOT:PSS by mechanical stirring and sonication processes. Schottky diodes were fabricated with these mixtures. The forward current of Schottky diodes fabricated with PEDOT:PSS dispersed BMI PF6 (SD-BMIPF6)/BMICL (SD-BMICL) by mechanical stirring is slightly reduced compared with that of Schottky diodes fabricated with pristine PEDOT:PSS (SD-PEDOT). However, SD-BMIPF6 and SD-BMICL by sonication technique show higher forward current with respect to SD-PEDOT. Compared with SD-BMIPF6 and SD-BMICL, the forward current of SD-BMICL is much higher than that of SD-BMIPF6. Since the BMICL has hydrophilic nature, the enhancement of forward current might be due to the uniform dispersion of the BMICL on the PEDOT:PSS matrix.     

Direct assembly process: a novel fabrication technique for large strain ionic polymer transducers

Ionic polymer transducers (IPT) consist of an ion-exchange membrane plated with flexible conductive electrodes on their outer surface. Compared to other types of electromechanical transducers, ionomeric transducers have the advantage of high-strain output (>9%), low-voltage operation (<5 V), and high sensitivity in the charge-sensing mode. A novel fabrication technique for ionic polymer transducers named the Direct Assembly Process (DAP) was developed in this paper. The DAP allows the use of any type of ionomer, diluent, and conducting powder in the transducer, and permits the exploration of any novel ionomeric design. In this paper the effect of diluent content of the IPT, electrode thickness, and composition were optimized in term of maximum peak strain and strain rate generated by an IPT. Decreasing viscosity and increasing polarity and content of the diluent were demonstrated to increase the strain rate of an IPT. The thickness of the electrode was varied and correlated with the maximum strain generated due to a 2 V step input. This study also demonstrated that RuO₂ composition has an optimal loading of 42 vol%, while SWNT electrodes have an optimal performance at around 30 vol%.