Chiara Zanardi

Electrochemical preparation and characterisation of bilayer films composed by Prussian Blue and conducting polymer

Abstract Preparation and electrochemical behaviour of bilayer films consisting of iron(III) hexacyanoferrate, well known as Prussian Blue, and of poly[4,4 ′ -bis(butylsulphanyl)-2,2 ′ -bithiophene], on a platinum electrode, are reported. The electrochemical features of the Prussian Blue/conducting polymer bilayer system are examined in aqueous and acetonitrile solutions. Cyclic voltammetric studies show that, in acetonitrile solvent, the inner layer Prussian Blue is electroactive to some extent, though the electrochemical response of the system is mainly accounted for by poly[4,4 ′ -bis(butylsulphanyl)-2,2 ′ -bithiophene] outer layer. On the other hand, in aqueous solution Prussian Blue exhibits good electroactivity. Under specific experimental conditions, the individual redox behaviour of each constituent of the bilayer is evidenced in the two solvents separately, i.e., that of PB and that of poly[4,4 ′ -bis(butylsulphanyl)-2,2 ′ -bithiophene] in aqueous and in organic solvent, respectively. However, interesting reciprocal influences are evident in the current/potential curves recorded under conditions which are discussed.

Polythiophenes and polythiophene-based composites in amperometric sensing

AbstractThis overview of polythiophene-based materials provides a critical examination of meaningful examples of applications of similar electrode materials in electroanalysis. The advantages arising from the use of polythiophene derivatives in such an applicative context is discussed by considering the organic conductive material as such, and as one of the components of hybrid materials. The rationale at the basis of the combination of two or even more individual components into a hybrid material is discussed with reference to the active electrode processes and the consequent possible improvements of the electroanalytical performance. In this respect, study cases are presented considering different analytes chosen among those that are most frequently reported within the classes of organics and inorganics. The use of a polythiophene matrix to stably fix biological elements at the electrode surface for the development of catalytic biosensors and genosensors is also discussed. Finally, a few possible lines along which the next research in the field could be fruitfully pursued are outlined. Furthermore, the work still to be done to exploit the possibilities offered by novel products of organic synthesis, even along paths already traced in other fields of electrochemistry, is discussed. Prototypical voltammetric responses obtained in a solution of two analytes on: bare electrode (left); polythiophine-based coated electrode (right).

Polythiophene Derivative Conducting Polymer Modified Electrodes and Microelectrodes for Determination of Ascorbic Acid. Effect of Possible Interferents

Conventional-size electrodes and microelectrodes coated by electrogenerated poly[4,4′-bis(butylsulfanyl)-2,2′-bithiophene] have been tested with respect to the electrocatalytic oxidation of a particularly interesting analyte, i.e., ascorbic acid, in different concentrations of phosphate buffer, aqueous solution. Linear sweep and cyclic voltammetry have been used and the quantities related to the analyte concentration were the peak current and the diffusion (t−1/2) deconvoluted peak current in the case of conventional-size and of microelectrode, respectively. Fairly good linear correlation could be found; a particularly wide linearity range was obtained by working with the microelectrode. It showed to give good results also at a very low (10−4 M) phosphate buffer-supporting electrolyte concentration. The actual interference on the analysis of compounds often coupled with ascorbic acid in natural or pharmaceutical products has been studied.

Amperometric sensors based on poly (3,4-ethylenedioxythiophene)-modified electrodes: Discrimination of white wines

The voltammetric responses on selected white wines of different vintages and origins have been systematically collected by three different modified electrodes, in order to check their effectiveness in performing blind analysis of similar matrices. The electrode modifiers consist of a conducting polymer, namely poly(3,4-ethylenedioxythiophene) (PEDOT) and of composite materials of Au and Pt nanoparticles embedded in a PEDOT layer. Wine samples have been tested, without any prior treatments, with differential pulse voltammetry technique. The subsequent chemometric analysis has been carried out both separately on the signals of each sensor, and on the signals of two or even three sensors as a unique set of data, in order to check the possible complementarity of the information brought by the different electrodes. After a preliminary inspection by principal component analysis, classification models have been built and validated by partial least squares-discriminant analysis. The discriminant capability has been evaluated in terms of sensitivity and specificity of classification; in all cases quite good results have been obtained.

Classification of red wines by chemometric analysis of voltammetric signals from PEDOT-modified electrodes

Nine different types of Italian red wines of four different varieties were analysed, without any sample pre-treatments, by voltammetric techniques using a poly(3,4-ethylenedioxythiophene)-modified electrode. The data matrices consisting of the currents measured at different potentials, by repeated Cyclic Voltammetry or Differential Pulse Voltammetry, are submitted to chemometric analysis. After explorative tests based on Principal Component Analysis, Partial Least Squares-Discriminant Analysis classification models are built both for the training and for the test sets. To this aim, different classification strategies are adopted, considering the responses from the two techniques either separately or joined together to form a data matrix including the whole voltammetric information.

p- and n-doping processes in polythiophene with reduced bandgap. An electrochemical impedance spectroscopy study

Abstract Electrochemical impedance spectroscopy has been used for the characterisation of electrodes modified with different polythiophenes, namely poly[4,4′-bis(butylsulfanyl)-2,2′-bithiophene], poly[4,4′-bis(methylsulfanyl)-2,2′-bithiophene] and poly(3-methylthiophene), at different applied potentials, using different supporting electrolytes. By comparison of the results obtained under experimental conditions in which n-doping is prevented and those obtained from tests where it does occur, some general features have been deduced, all of them being coherently described by a recently proposed ‘generalised transmission line circuit’ model: impedance plots at different applied potentials exhibit progressive changes which are well accounted for by the ‘evolving’ model. The results obtained on the n-doping process of S -alkyl substituted polymers suggest a behaviour interestingly similar to that exhibited in the p-doping; this supports a symmetry that was also found by us in a previous work, with respect to the incorporation and release of counterions during the n- and p-charge–discharge processes.

Density and volumetric properties of ethane-1,2-diol + di-ethylen-glycol mixtures at different temperatures

Abstract The density of the ethane-1,2-diol (ED)+di-ethylen-glycol (DEG) binary mixtures has been measured at different temperatures over the complete composition range. The experimental measurements have been used to check the validity of relationships accounting for the dependence of the density on temperature and composition, useful to obtain interpolated values in the correspondence of the experimental data gaps. Starting from the primary data, some derived quantities, such as partial molar volumes, excess and partial excess molar volumes, have been obtained. In these mixtures, VE presents an S-shaped dependence on composition at each temperature, showing negative values in the ED rich-region and positive values at the opposite extreme. The results are compared and discussed to get light to the changes in molecular association and structural effects in this solvent system.

Isolated single-molecule magnets on native gold

The incorporation of thioether groups in the structure of a Mn12 single-molecule magnet, [Mn12(O12)(L)16(H2O)4] with L = 4-(methylthio)benzoate, is a successful route to the deposition of well-separated clusters on native gold surfaces and to the addressing of individual molecules by scanning tunnelling microscopy.

Synthesis and electrochemical characterisation of novel sonogel–carbon–polythiophene microstructured electrodes

Abstract A sonogel–carbon–polythiophene microstructured electrode has been synthesised via sonocatalytic procedure. The composite material was characterised by cyclic voltammetry, atomic force microscopy and optical microscopy. A comparison with a similar polythiophene directly cast on a platinum electrode has been made. In contrast with the degrading behaviour (overoxidation) observed at sufficiently positive potentials for alkylsulphanyl substituted polythiophenes cast on the electrode surface, the entrapment of the polymer inside a composite material drastically enhances the stability of the redox-active phase towards irreversible oxidation. In addition, the sonogel–carbon–polythiophene composite represents a good approach to test and, possibly, exploit the electrochemical properties of the polymer which, due to its complete insolubility in the common organic solvents, cannot be adequately cast on an electrode surface or electrosynthesised.

Electropolymerisation and characterisation of poly[4,4′-bis(butylsulphanil)-2,2′-bithiophene]

Abstract Electrochemical properties of electrogenerated poly[4,4′-bis(butylsulphanil)-2,2′-bithiophene] have been studied, with particular attention to the charge-discharge processes. The possibility of both p- and n-doping is indicated. Doping and relevant de-doping processes of the specific polymer have also been considered in the context of the more general, still un-solved problem of the analysis of the mechanisms that are operative in the case of simple polythiophenes. In situ spectroelectrochemical measurements have been used to support the electrochemical results and both in situ UV–visible–NIR spectroscopy on neutral, p- and n-doped forms of the polymer, and ex situ IR measurements have been performed.