Electrochemical sensors conductive polymeric films

Among the conjugated polymers, polypyrrole (PPy) is the most representative one for its easy polymerization and wide application in gas sensors, electrochromic devices and batteries. Polypyrrole can be produced in the form of powders, coatings, or films. It is intrinsically conductive, stable and can be quite easily produced also continuously. The preparation of polypyrrole by oxidation of pyrrole dates back to 1888 and by electrochemical polymerization to 1957. However, this organic p>-system attracted general interest and was foimd to be electrically conductive in 1963. Polypyrrole has a high mechanical and chemical stability and can be produced continuously as flexible film (thickness 80 mm trade name Lutamer, BASF) by electrochemical techniques. Conductive polypyrrole films are obtained directly by anodic polymerization of pyrrole in aqueous or organic electrolytes. 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

For electrochemical sensors, the ECP-CNT/GO composites can be deposited either as thin films on solid substrates or incorporated in conventional host polymeric materials. To further increase the electrical conductivity of the ECP-GO composites, the electrically non-conducting GO in the composites matrix can be converted chemically or electrochemically to reduced GO (RGO], which is electrically conducting [15]. During the reduction, most of the oxygen-containing groups are removed from the GO surface, which partially restores the sp hybridization of the carbon atoms and increases the electrical conductivity of the material. 

Nanocable chemosensors have been formed in which an inner core fiber filament is further modified by polymerization of the conducting polymer on its surface. This was first described for sensing by Zhang et al. in which a carbon fiber was used as the template for the electrochemical polymerization of a thin film of PANI [27]. The resulting nanoelectrode sensor was used to detect changes in pH resulting from the level of protonation in the polymer backbone. PPy nanofibers have been formed by the electrospinning of nylon fibers. 

Currently available amperometric and voltammetric porphyrinic sensors for detection of electroactive analytes are based on their electrochemical oxidation or reduction on polymeric conductive films of metalloporphyrins. If the current generated during the process is linearly proportional to the concentration of an andyte, the current can be used as an analytic signal. This current can be measured in either the... 

This report describes some of the recent work on the electrochemical and electrode applications of polymers which are electroactive and can be switched to an electrically conductive state, as well as the inherently conductive (SN. The materials fall into two general categories. There are the polymer tllms which can be prepared in situ by the electrochemical polymerization of aromatic compounds, and there are the polyenes such as polyacetylene and polythiazyl. Many of the electrode applications being considered are based on the. electroactive/conductive properties of the films such as display devices, and storage batteries. Some applications make use of the conductive property of the materials such as protective coatings against corrosion, and other applications make use of the possibility for molecular selectivity such as chemically selective electrodes and sensors. 

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