Conducting Polymer Matrix Research Articles

Impedance labelless detection-based polypyrrole DNA biosensor

Microelectrodes were fabricated to study impedance labelless detection of DNA hybridization. The probe molecule was attached onto the platinum microelectrode surface by electrochemically copolymerizing pyrrole and the probe oligonucleotides. Measured impedance complexes showed that an electrochemical redox-reaction occurred and the electron-transfer resistance increased after DNA hybridization. It was proposed that the hybridization of DNA in the conductive polymer matrix slowed down the anionic doping/undoping process, resulting impedance changes for the target DNA detection. Impedance measurements were conducted at the complementarily hybridized probe oilgomer-attached polypyrrole film electrodes in different anionic solutions to exam the anionic effects. Results showed that higher concentration and smaller size of anions had the lower electron-transfer resistance. The results not only provide further evidence to support the detection mechanism proposed, but also offer a method to improve the signal to noise ratio for the DNA biosensor. The research also tested the specificity of the methods and experimental results, indicating good specificity of the method. A concept array chip was fabricated and used to demonstrate the capability of the labelless detection method. Nano-Molar concentrations were detected and showed fairly linear responses versus the target molecule concentrations. The method is simple and inexpensive. The technique based genosensors could have potential applications in clinical diagnosis, drug discovery, environmental and food analysis.

Key role of the desolvation in the achievement of the quasi-metallic state of electronically conducting polymers

Redox transformation of electronically conducting polymers was studied by different in situ combined electrochemical techniques. Results obtained with polypyrrole/dodecyl sulfate film in aqueous solution and with polythiophene/hexafluorophosphate films in acetonitrile by in situ ac conductance and EQCM support the assumption of the key role of the desolvation in the achievement of the so-called quasi-metallic state of electronically conducting polymers. The desolvation considered as a phase transition is the chemical background of the capacitive behaviour, and it causes the structural changes, which lead to a film in which the interchain interactions may form the large-scale conducting polymer matrix.

Conductive polymer-modified boron-doped diamond for DNA hybridization analysis

In this paper, we study the immobilization of DNA on boron-doped diamond (BDD) thin films for DNA hybridization analysis. Taking advantage of the conducting nature of the BDD film, a thin layer of polyaniline/poly (acrylic acid) (PANI/PAA) composite polymer film could be readily electropolymerized onto the diamond surface. The carboxylic acid residues in the polymer film act as the binding sites for DNA attachment, whilst the conductive polymer matrix enhances the electron-transfer between DNA and the diamond surface. Fluorescence microscopy and cyclic voltammetry measurements indicate that the polymer-modified BDD has minimal non-specific DNA adsorption, and provides a stable transduction platform for DNA sensing.

A PbS quantum-cube: conducting polymer composite for photovoltaic applications

We have developed a new non-polar synthesis for lead sulfide (PbS) “quantum-cubes” in the conjugated polymer poly-2-methoxy,5-(2-ethyl-hexyloxy-p-phenylenevinylene) MEH-PPV. The conducting polymer acts to template and control the quantum-cube growth. Transmission electron microscopy of the composites has shown a bimodal distribution of cube sizes between 5 and 15 nm is produced with broad optical absorption from 300 to 650 nm. Photoluminescence suggests electronic coupling between the cubes and the conducting polymer matrix. The synthesis and initial characterization are presented in this paper.

Novel label-free DNA sensors based on poly(3,4-ethylenedioxythiophene)Electronic Supplementary Information (ESI) available: Experimental details and sensor response for various sensors listed in Table 2. Cyclic voltammograms confirming the increase in resistance due to the duplex formation between the probe and target DNA in conducting polymer matrix. See http://www.rsc.org/suppdata/cc/b3/b316794a/

We report on the design and development of a novel label-free DNA sensor based on conducting poly(3,4-ethylenedioxythiophene) for the direct detection and quantification of target ssDNA.

Noncovalent Functionalization of Single Walled Carbon Nanotubes Using Alternate Layer-By-Layer Polyelectrolyte Adsorption for Nanocomposite Fuel Cell Electrodes

ABSTRACTElectrodes which are resistant to chemical poisoning by CO, S, and other fuel impurities are needed to replace Pt in proton exchange membrane (PEM) fuel cells. We have designed composite electrodes comprised of single walled carbon nanotubes (CNTs) within a conducting polymer matrix. A method for solubilizing single-walled carbon nanotubes (CNTs) in aqueous media using polyelectrolyte layer-by-layer (LbL) nanoassembly of polystyrene sulfonate (PSS) and polyallylamine (PAH) at the CNT surface is elucidated. Once soluble, the CNTs were assembled onto planar substrates using alternate LbL nanoassembly to form nanocomposite films. These films will later be tested for their potential as alternative anodes in proton exchange membrane fuel cells.

Hydrogels of a conducting conjugated polymer as 3-D enzyme electrode

We have utilized the highly conducting poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) aqueous dispersion (PEDOT/PSS) to build a conducting hydrogel matrix. Together with appropriate biomolecules this constitutes a hydrogel bio-electrode. The open hydrogel structure makes diffusion of analytes surrounding the cells into the matrix electrode easier. If enzymes are utilized, osmium is used as mediator between the prosthetic group of the enzyme and the conducting polymer matrix. Osmium also functions as a crosslink point to poly-4-vinylpyridine, which together with the magnesium crosslinked PEDOT/PSS gives a rigid hydrogel. The enzyme Horseradish peroxidase (HRP) was used as a model enzyme to evaluate the enzyme-enhanced electrode. We evaluated the electrode at pH 7, which is the pH choice for many biological systems. From cyclic voltammetry (CV) measurements we deduced that a very low reduction potential was needed to reduce the prosthetic group. Constant potential amperometry were performed to demonstrate the biosensor capabilities. A differential sensitivity of 0.13 A M −1 cm −2 through the 0–30 μM concentration range was achieved. Both the biostability and the influence on conductivity, important aspects when for example making nerve- or cell-electrodes, were investigated.

PEDOT/PSS hydrogel networks as 3-D enzyme electrodes

A mesoscopic network in the form of a hydrogel of the highly conductive polymer PEDOT/PSS hydrogel was used in an enzyme electrode setup. Osmium was used both as a crosslink point in the hydrogel network and as a mediator between the prosthetic group of the enzyme and the conductive polymer matrix. Both biostability and high conductivity is important aspects when building nerve- or cell- electrodes. Diffusion of analytes surrounding the cells into the matrix electrode is feasible due to the open hydrogel structure. The high water content in these structures is important when buffering them to a pH of choice.

Hybrid organic–inorganic nanocomposite materials for application in solid state electrochemical supercapacitors

Integration into a conducting polymer matrix to form a hybrid material is an effective way to harness the electrochemical activity of nanosized oxide clusters. By anchoring them into polyaniline, the reversible redox chemistry of the otherwise soluble polyoxometalate clusters can be combined with that of the conducting polymer and be put to work in energy storage applications. We present here preliminary results that show how the resulting hybrid polymer displays the combined activity of its organic and inorganic components to store and release charge in a solid state electrochemical capacitor device.

A Variational Solution of the Thermoelectric Transport Properties of Two-Component Nanocomposite Systems

ABSTRACTThe successful fabrication of a nanocomposite in bulk form consisting of a randomly oriented assembly of nanoscale sized core-shell particles has required an increased understanding of the theoretical aspects of the thermoelectric transport properties. Our particular nanocomposite consists of a nanorod core in 1D quantum confinement coated with an outer conducting polymer shell. Upon fabrication of the bulk composite, these nanorods are embedded within a three-dimensional conducting polymer matrix. We address the nanorod thermoelectric components by assuming a single parabolic band within the one-dimension density of states. Both elastic and inelastic scattering of electrons or holes is accommodated by solving the variational form of the Boltzmann transport equation. An altered lattice thermal conductivity for the confined nanorods is calculated separately to account for boundary scattering that is important in low dimension structures. Exact expressions for the bulk effective electrical and thermal conductivities, Seebeck coefficient and figure of merit are then obtained through the field decoupling transformation, which is a special case of two-component composites. Our method is easily generalized to any two component composite of spherical or cylindrical microstructure and is independent of the materials bulk geometry. The results similarly apply to one, two or three dimensional transport regimes with or without quantum confinement merely by solving the appropriate fundamental transport equations for each constituent material. Comparison to experimental data is then presented which helps validate the nanocomposite theory.

Apparent dependence of conductivity of a conducting polymer on an electric field in a field effect transistor configuration

A curious effect is reported whereby an electric field apparently greatly affects the conductivity of an organic polymer, poly-3,4-ethylenedioxythiophene (PEDOT), doped to the “metallic” conducting regime when it is used in an all-organic polymer field effect transistor configuration. The response time for change in current in the source/drain PEDOT polymer with a change of gate voltage is slow (⩽∼2 s), suggesting that ionic diffusion is involved in the phenomenon. It is suggested that the electric field changes only the conductivity of the lowly conducting polymer matrix, which contains highly conducting islands of PEDOT, thus changing the extent of percolation of electric charge between metallic islands, and thereby affecting the bulk conductivity of the PEDOT source/drain material.

Novel polymer electrolytes prepared by copolymerization of ionic liquid monomers

AbstractIonic liquid monomer couples were prepared by the neutralization of 1‐vinylimidazole with vinylsulfonic acid or 3‐sulfopropyl acrylate. These ionic liquid monomer couples were viscous liquid at room temperature and showed low glass transition temperature (Tg) at −83 °C and −73 °C, respectively. These monomer couples were copolymerized to prepare ion conductive polymer matrix. Thus prepared ionic liquid copolymers had no carrier ions, and they showed very low ionic conductivity of below 10−9 S cm−1. Equimolar amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to imidazolium salt unit was then added to generate carrier ions in the ionic liquid copolymers. Poly(vinylimidazolium‐co‐vinylsulfonate) containing equimolar LiTFSI showed the ionic conductivity of 4 × 10−8 S cm−1 at 30 °C. Advanced copolymer, poly(vinylimidazolium‐co‐3‐sulfopropyl acrylate) which has flexible spacer between the anionic charge and polymer main chain, showed the ionic conductivity of about 10−6 S cm−1 at 30 °C, which is 100 times higher than that of copolymer without spacer. Even an excess amount of LiTFSI was added, the ionic conductivity of the copolymer kept this conductivity. This tendency is completely different from the typical polyether systems. Copyright © 2002 John Wiley & Sons, Ltd.

GaSb-based Nanocomposites as IR-Emitters

ABSTRACTNanocomposites consisting of GaSb nanocrystals in a conducting polymer matrix were fabricated and investigated. The current-voltage characteristics of the nanocomposite-based diode structures have a symmetric but strongly nonlinear character. Capacitance-voltage characteristics of the structures were investigated both in the dark and under illumination and compared with those of a pure polymer. At applied voltages exceeding 7–10 V (for different samples) electroluminescence begins and steeply increases. The position of the maximum of the measured electroluminescence spectra can be made to vary in the 1.3 – 1.6 μm wavelengths region by changing nanocrystal size. Photoluminescence spectra have a maximum nearly coinciding with that of electroluminescence but of considerably larger width. The results demonstrate the promise of GaSb-based nanocomposites for infrared light-emitting devices operating in the 1.3–1.6 μm spectral region used in optical communication systems.

Carrier transport and luminescence in composite organic–inorganic light-emitting devices

A model is presented to explain the light-current–voltage characteristics of composite light-emitting structures. These structures are composed of a conducting polymer matrix impregnated with a sheet of inorganic quantum dot nanocrystals. Such structures were reported to exhibit emission characteristics which were extremely promising but, at the same time, not explicable using available models. We present a generalized model that can describe the salient observed characteristics.

Electrocatalytic properties of the ion beam irradiated conducting polypyrrole

The electrocatalytic property of the conducting polypyrrole (PPy) films doped with palladium chloride and irradiated with heavy ion beams was studied for methanol oxidation. The PPy films were electropolymerized on gold film coated glass plate electrodes, subsequently doped with different amounts of PdCl 2 and then irradiated with 120 MeV, Au + ions at a dose of 10 12 ions/ cm 2 . The cyclic voltammograms (CVs) of these samples for methanol oxidation in 0.1 M HClO 4 showed a four times increase in the anodic current as compared to the un-irradiated ones. These improvements in the electrocatalytic activity by ion beam irradiation could be associated with better complex formation between the dopant and conducting polymer matrix which was confirmed by the X-ray photoelectron spectroscopy (XPS) studies.

Recognition of alcohol vapor molecules by simultaneous measurements of resistance changes on polypyrrole-based composite thin films and mass changes on a piezoelectric crystal

A novel gas sensor is fabricated on the basis of simultaneous measurements of resistance changes on polypyrrole-based composite thin films and frequency changes on a piezoelectric crystal. Molecular species such as ethanol and methanol can be recognized by the (Δ R/Δ f) values, where Δ R and Δ f are the resistance and frequency change, respectively. The Δ R/Δ f value remaining constant at various concentrations of detected gases is a characteristic index of a given kind of vapor molecules. The Δ R/Δ f value can be modified by the introduction of inert materials, including poly(ethylene oxide) (PEO) and polyacrylonitrile (PAN), into the conducting polymer matrix. The higher the Δ R/Δ f value, the better is the recognition ability. The composite PPy/PEO (PEO=7 g/l) film exhibits the best recognition for alcohol vapor molecules among the investigated sensing films. Meanwhile, the quantitative analysis of the vapor molecules can be achieved by measuring the Δ R or Δ f values.

Conductivity of conductive polymer for flip chip bonding and BGA socket

Numerous experimental studies on electrically conductive polymer have showed that the flip chip bonding and BGA socket with conductive polymers have a certain amount of contact resistance between contact pad and conductive polymer and among fillers, in addition to bulk resistance of fillers themselves. The ingress of insulating films into the contact area results in an increase of contact resistance. Conductive polymer generally consists of conductive filler and adhesive polymer matrix. Its conductivity depends not only on filler material, filler ratio, and operating environment, but also on filler packing structure, voltage drop and mechanical stress due to the mismatch of materials’ coefficients of thermal expansion, which results in the deformation of the chip, substrate and printed circuit board. In this paper, an analysis, based on fundamental electrical contact physics, material kinetics and particle packing structure, was conducted to deepen our understanding into the correlation between the conductivity of polymer bonding system and such key variables as filler packing configuration, stress, voltage drop and operating environment.

Mixed (ionic and electronic) conductive solid polymer matrix. Synthesis and characterization of homopolymers of 3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene and copolymers with 3-methylthiophene

Mixed (ionic and electronic) conductive solid polymer matrix. Synthesis and characterization of homopolymers of 3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene and copolymers with 3-methylthiophene

Mixed (ionic and electronic) conductive solid polymer matrix. Synthesis and characterization of homopolymers of 3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene and copolymers with 3-methylthiophene

The macromonomer, 3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene, abbreviated as (3-OHDT), was synthesized. The macromonomer has a glass transition temperature of –77°C, which corresponds to the soft oligooxyethylene side chain attached to the thiophene. The homopolymer, poly[3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene], abbreviated to P[3-(OHDT)], has been synthesized via oxidative coupling of the macromonomer using FeCl3. Two distinct glass transition temperatures are observed for the homopolymer. The Tg at –47°C corresponds to the soft oligooxyethylene phase and the Tg value at 72°C corresponds to the hard thiophene backbone. The homopolymer P[3-(OHDT)] can be doped with LiClO4 and I2 to generate ionic and electronic conductive phases, respectively. For the P[3-(OHDT)]/LiClO4 system, with an ethylene oxide to lithium mole ratio of 8 : 1, an ionic conductivity value of 1.7×10–6 S cm–1 is observed at 25°C. The room temperature electronic conductivity of P[3-(OHDT)]/doped with I2 is 3.5x10–4 S cm–1. Several random copolymers of 3-methylthiophene and 3-(2,5,8,11,14,17,20,23-octaoxyhexadodecyl)thiophene were also synthesized. Depending on the copolymer composition, glass transition temperatures ranged from 67°C to 76°C, the higher glass transition temperature corresponding to higher 3-methylthiophene content. The copolymers may be appropriately doped to generate conductive matrices, with a maximum ionic conductivity (ethylene oxide/Li+ mole ratio of 8 : 1) of 1.0×10–7 S cm–1 and electronic conductivity around 6.7×10–1 S cm–1 at 25°C.

Enhanced Electron Transfer Reaction of Myoglobin in PEO by DNA/Bisbenzimide Complex

Double-stranded DNA was used as a molecular wire to enhance the electron transfer reaction between PEO-modified myoglobin (PEO-Mb) and electrode in PEO oligomers. No acceleration but suppression of electron transfer was found when only DNA was used. The π stacking of base-pairs in DNA was enhanced by the complexation with bisbenzimide. Larger current of PEO-Mb was found under suitable values of the molar ratio of bisbenzimide to DNA base pair, the quantity of cast PEO-Mb, and the ratio of DNA base pair to PEO-Mb. DNA/bisbenzimide complex was revealed to be effective for the electron transfer reaction between heme-proteins and electrode even in ion conductive polymer matrix.