Advances on rigid conducting composites for electroanalytical applications

The development of composites based on conductive phases dispersed in polymeric matrices has led to important advances in analytical electrochemistry. Composite materials based on different forms of carbon as conductive phase have played a leading role in the analytical electrochemistry field, particularly in sensor devices. These materials combine the electrical properties of graphite and carbon nanotubes with the ease of processing of plastics (epoxy, methacrylate, Teflon, etc.). They show attractive electrochemical, physical, mechanical and economical features compared to the classic conductors (gold, platinum, graphite, etc.). Considering carbon composite in generally, their electrochemical properties present improvements over conventional solid carbon electrode, such as glassy carbon. The properties of these composites based are described, along with their application to the construction of electrochemical sensors. The carbon-based composites exhibit interesting advantages, such as easy surface renewal, as well as low background current. Depending also on the conductive load, composites can behave as microelectrode arrays which are known to provide efficient mass transport of the electroactive species due to radial diffusion on the spaced carbon particles. Such improved mass transport favors the sensitive electroanalysis of a variety of reagents, including electrocatalysts, enzymes and chemical recognition agents. Moreover, the carbon surface chemistry also influences significantly the electron transfer processes at these electrodes. During the past few decades, the electrochemical properties of different graphite powder composite materials based on different kinds of polymeric matrices were studied in detail. Nowadays, high interest is focused on composites based on carbon nanotubes (CNTs). They are attractive materials due to their remarkable mechanical and electrical properties. They have a highly accessible surface area, low resistance, high mechanical and chemical stability and their performance had been found to be superior to the other kinds of carbon material. The main drawback in CNT composite materials reside in the lack of homogeneity of the different commercial CNT lots due to different amount of impurities in the nanotubes, as well as dispersion in their diameter/length and state of aggregation (isolated, ropes, bundles). These variations are difficult to quantify and make mandatory a previous electrochemical characterization of the composite, before being used as a chemical sensor. Another important point of consideration is the optimization of the conducting material (graphite or CNTs) loading in the composite materials for improving their electrochemical properties and analytical applications. Therefore, in this chapter we will describe the strategy to find the optimum composite proportions for obtaining high electrode sensitivity, low limit of detection and fast response. Compositions of composites can be characterized by percolation theory, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, atomic force microscopy and chronoamperometry. Moreover, the optimized carbon-based composite electrodes can be integrated in a continuous flow analytical system, as a flow injection analysis (FIA) or a miniaturized device, to take advantage of all the benefits provided by these automatization techniques. © 2011 by Nova Science Publishers, Inc. All rights reserved.