Wolfgang Wernet

Stability of polypyrrole and poly(3,4-ethylenedioxythiophene) for biosensor application

Abstract The electrochemical polymerization of pyrrole and 3,4-ethylenedioxythiophene (EDT) in phosphate buffer solutions in the presence of poly(styrene sulfonate) (PSS) was investigated by means of cyclic voltammetry and chronoamperometry. From the measurements it was found that the electrochemical polymerization of pyrrole and EDT could be initiated at 600 mV and 800 mV respectively in the phosphate buffer. To evaluate the stability of polypyrrole + poly(styrene sulfonate) (PPy + PSS) and poly(3,4-ethylenedioxythiophene) + poly(styrene sulfonate) (PEDT + PSS) films, a constant potential was applied to films immersed in phosphate buffer solutions. PEDT + PSS was found to be much more stable than PPy + PSS under constant polarization conditions. After polarization for 16 h at 400 mV and pH 7.5 only 5% of the original electrochemical activity of PPy + PSS remained, whereas PEDT + PSS retained 89% of its original activity. The stability is strongly dependent on the magnitude of the polarization potential and the pH of the buffer solution.

A highly sensitive amperometric creatinine sensor

Abstract Highly sensitive amperometric creatinine sensors based on the adsorption of three enzymes are described. The base electrodes are fabricated using electrochemical deposition of Pt black on a flexible electro-conductive polymer film (polyanion doped polypyrrole). The multienzyme system (creatininase, creatinase and sarcosine oxidase) is adsorbed at the Pt black matrix. After drying a thin gelatin layer is cast on the enzyme adsorbed film and cross-linked under dry conditions by dipping into a diluted glutaraldehyde solution for 30 s. The sensor performance is evaluated using a batch analysis and a stop flow analysis by applying a continuous polarization potential of 0.4 V vs. Ag AgCl at 25 °C. The sensitivity of the developed sensors is dependent on the preparation condition, the source of sarcosine oxidase, the composition of the three enzymes in the adsorbing/casting solution and the Pt black loading. A sensitivity of 23 μA/mM cm−2 and an extended linear range upto 5 mM level with a detection limit of 1–2 μM are obtained. At certain compositions of these three enzymes creatine does not produce any significant response current up to the physiological maxima of 1 mM, which makes the system virtually free from creatine interference. The operational stability of the response current of the developed sensor is also described.

Platinization of Shapable Electroconductive Polymer Film for an Improved Glucose Sensor

This paper describes a novel electrode material for the preparation of a first generation amperometric biosensor. The material consists of a flexible conductive polymer film of polypyrrole doped with polyanions and a layer of microporous Pt black, prepared electrochemically on the polymer film. Sensors fabricated with this material produce a comparatively higher H 2 O 2 oxidation current at a lower applied potential. Glucose sensors were prepared by adsorbing glucose oxidase at the porous Pt black structure, covering with gelatin, and finally cross-linking with glutaraldehyde at dry condition. The developed sensors showed significantly improved performance over similar reported sensor systems. The performance of the glucose sensor was evaluated by a specially designed flow injection analysis (FIA) system. The sensors were continuously polarized at 25°C and glucose samples were automatically injected at 30 min intervals. The sensors worked at 0.3 to 0.4 V and produced a huge current response (>1 mA/cm 2 ) with a wide linear range of detection (0 to 100 mM). The system effectively recycles oxygen, thus, the response current was not affected by a variation of oxygen concentration of the buffer. The interference of ascorbic acid, uric acid, bilirubin, etc. (at a physiological level) produced a current within the experimental error level. The sensor showed an extended working and shelf life.

A new method for dispersing palladium microparticles in conducting polymer films and its application to biosensors

Abstract Composite films of polypyrrole/sulfated poly(β-hydroxyethers) (PPy/S-PHE) are electrically conducting and mechanically flexible. Palladium particles were dispersed in the films by thermally decomposing bis(dibenzylideneacetone)palladium(0) complex which had been absorbed by the films from a CHCl3 solution. This method for loading metal particles was enabled by the high affinity of the composite films for organic compounds. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectrometry (EDX) analyses revealed that fine palladium particles in the nanometer range are dispersed in the PPy/S-PHE conducting films. A glucose sensor based on the detection of hydrogen peroxide was prepared by immobilizing glucose oxidase (GOD) using glutaraldehyde on a Pd/PPy/S-PHE electrode. This biosensor responded to glucose even at 400 mV versus Ag/AgCl, which is lower than the working potential of conventional glucose sensors prepared on a platinum electrode.

Synthesis of free-standing poly(3,4-ethylenedioxythiophene) conducting polymer films on a pilot scale

Abstract Electrochemical polymerization of 3,4-ethylenedioxythiophene (EDT) was carried out in the presence of monomeric anions or polyanions in electrolyte solutions. While no free-standing films of poly (3,4-ethylenedioxythiophene) (PEDT) were obtained using monomeric anions as dopants, flexible conducting polymers were obtained using novel polyanions, e.g., sulfated poly(β-hydroxyethers) (S-PHE), sulfated poly(β-hydroxyethers) having trifluoromethyl groups (S-PHEF), and sulfated polybutadiene (S-PBD). The conductivity of these PEDT/ polyanion composites exceeded 150 S/cm, and reached as high as 400 S/cm when S-PHEF was used as dopant. These conducting composites demonstrated superior mechanical properties, and PEDT/S-PBD showed an elongation of 78–110% at 100 °C. The electrical properties were strongly dependent on the synthesis conditions. The important parameters were optimized for the S-PHE polyanion. By doing this the conductivity of the PEDT/S-PHE composite reached values around 230 S/cm. Based on the optimized parameters, a continuous synthesis of PEDT/S-PHE composite was developed leading to reproducible conducting composites. The electrode is cylindrical and 10 cm wide. The computer-controlled system enabled the preparation of PEDT films more than 20 m long.

Mechanical, electrochemical and optical properties of poly(3,4-ethylenedioxythiophene)/sulfated poly(β-hydroxyethers) composite films

Abstract Poly(3,4-ethylenedioxythiophene)/sulfated poly(β-hydroxyethers) (PEDT/S-PHE) composite films were prepared by electrochemical polymerization of 3,4-ethylenedioxythiophene (EDT) in the presence of S-PHE poly electrolytes. The sulfate groups of S-PHE play the role of the counterion to the positive charges of the oxidized PEDT. Moreover, as a consequence of the good mechanical properties imparted by S-PHE we succeeded in preparing free-standing PEDT composite films. All composites showed excellent mechanical properties, high conductivity and reversible electrochromic properties. In order to examine the influence of the S-PHE content on composite properties, a series of composites containing S-PHEs of differing molar ratios (MR) of sulfate groups to the monomer units of poly(β-hydroxyethers) were synthesized. From the experimental results it was found that the conductivity of the composites is independent of MR value and, hence, PEDT content. In situ absorption spectra of the composite films suggested that composites with larger contents of PEDT possessed shorter π-conjugation lengths. Electrochemical properties of the composites were measured by means of cyclic voltammetry and potential step chronocoulometry and results demonstrated that the rate of switching between the doped and undoped states of the composites occurs within 0.5 s. The absorption band of the composites in the visible region almost disappeared upon doping. All results indicate that the composites are interesting candidates as materials for electrochromic displays.

Thermoplastic and elastic conducting polypyrrole films

Abstract To improve the processability of intrinsically conducting polymers (ICP) we synthetized new polyelectrolytes (PEL) and used them in the electrochemical synthesis of polypyrrole (PPY). The chemical structures of the PELs are based on sulfated poly(β-hydroxyethers), poly-(butadienes), poly(imides) and poly(methacrylates). PPY-films made in the presence of this PELs show high conductivities and excellent processing properties.

Characterization of thermoplastic sulfated poly(β-hydroxyethers)/polypyrrole conducting composites

Abstract The influence of the molecular weight and the content of sulfate groups of sulfated poly(β-hydroxyethers) (S-PHE), used as dopants for polypyrrole, on the electrical and mechanical properties has been studied. It was found that the electrical conductivity of PPy/S-PHE decreased with increasing the molecular weight of S-PHE except when S-PHE with a high molar ratio of sulfation (MR) was used. The stretchability was influenced by the molecular weight as well as MR of the polyanions and exceeded 200% at a high molecular weight and a low molar ratio of sulfation. Electrochemical experiments showed a superiority of PPy/S-PHE in charge-discharge kinetics and practical charge capacity compared to polypyrrole/poly(styrenesulfonate) films.

Improvement of the properties of pyrrole intrinsically conducting polymers (ICP) with polyelectrolytes

Abstract Sulfated poly (β-hydroxyethers) (S-PHE) used as dopants in the polypyrrole (PPY) synthesis improve the mechanical properties like stretchability and flexibility of electrically conducting films. The influence of the molecular weight and the content of sulface groups of S-PHE-based polyelectrolytes used as dopants on the properties of the materials is shown. A possible application as cathodes in secondary batteries will be discussed.