Impedance analysis of the electrochemical doping of poly(3-methyl-thiophene) from aqueous nitrate solutions

Conduction and photoelectrochemical properties of monomeric and electropolymerized tetraruthenated porphyrin films

The influence of the preparation method on the structure, conduction and photoelectrochemical properties of monomeric and polymeric tetraruthenated porphyrin films on ITO glass and nanocrystalline TiO2 has been investigated. The films were characterized by STM, MAC mode SFM, cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and combined electro-/photoelectrochemical techniques. The electronic diffusion coefficient D(e)C(m)2 of the films differed by three to four orders of magnitude depending on the procedure employed for the deposition process. The photoelectrochemical properties were evaluated either: by depositing the films directly on transparent ITO electrodes, under an applied bias potential and presence of O2 as electron acceptor; or by depositing the porphyrin material on nanocrystalline TiO2 in a Grätzel-type cell. In the first case the porphyrin films exhibited a typical p-type semiconductor behavior described by a Schottky junction model, while in the second the films behaved as a sensitizer of an n-type semiconductor. The photoelectrochemical properties of the porphyrin films and their performance as sensitizer in Grätzel-type cells were found to be strongly dependent on the conductivity and packing characteristics of the material. Semi-empirical calculations were performed by modified MM2 and ZINDO/S methods, in order to simulate the packing and electronic structures of the tetraruthenated porphyrin.

Functional characterization of a conducting polymer-based immunoassay system

Experiments have been performed to characterize the electrical properties and functionality of a poly(3-hexylthiophene)-coated platinum electrode developed as a sensor for immunoassay read-out. Admittance measurements were performed on the coated electrodes as a function of frequency. The admittance spectra obtained show that the sensor is capacitive in nature. A circuit model is presented for comparison to other conducting polymer systems. Dynamic sensor response is characterized by oxidizing the polymer via a hydrogen peroxide-iodide pathway. Hydrogen peroxide is introduced either by direct injection or through a glucose-glucose oxidase reaction to determine electrode functionality and sensitivity. Sensor response to chemical oxidation is measured as a function of frequency and applied signal amplitude. System response is linear in frequency from 1 Hz to 70 Hz and in excitation amplitude up to approximately 600 mV. System sensitivity is analyzed based on oxidant generation from the enzyme-initiated pathway, sensor baseline drift, and the noise band on the quiescent sensor current.