Rigid carbon composites

Besides thick-layer DNA/GEC surface, a thin-layer DNA/GEC could be achieved by wet-adsorption of ss- and dsDNA and ODN onto a GEC transducer under static conditions [99,100]. In this case, the hydrated B-DNA form was stabilized over the GEC surface by weaker forces. Unlike the GEC surface modified by the thick DNA layer —produced in dry conditions—the thin-layer DNA/GEC surface required blocking treatment to avoid nonspecific 

Although DNA can be firmly adsorbed on GEC, it retains its unique hybridization properties, which can be monitored using various strategies [99, too], suggesting that the DNA bases are not fully committed in the adsorption mechanism. 

Moreover, the unique adsorption properties of GEC allowed the very sensitive electrochemical detection of DNA based on its intrinsic oxidation signal that was shown to be strongly dependent of the multi-site attachment of DNA and the proximity of G residues to GEC [100]. The thick layer of DNA adsorbed on GEC was more accessible for hybridization than those in nylon membranes obtained with genosensors based on nylon/GEC with a changeable membrane [99,101,102]. Allhough GEC has a rough surface, it is impermeable, while nylon is more porous and permeable. DNA assays made on an impermeable support are less complex from a theoretical standpoint [7] the kinetics of the interactions are not compUcated by the diffusion of solvent and solutes into and out of pores or by multiple interactions that can occur once the DNA has entered a pore. This explained the lower hybridization time, the low nonspecific adsorplion and the low quantity of DNA adsorbed onto GEC compared to nylon membranes. 

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M.I. Pividori and S. Alegret, Electrochemical genosensing based on rigid carbon composites. A review, Anal. Lett., 38 (2005) 2541-2565. 

A. Erdem, M.I. Pividori, M. Del Valle and S. Alegret, Rigid carbon composites a new transducing material for label-free electrochemical genosensing, J. Electroanal. Chem., 567 (2004) 29-37. 

Stable cycling was achieved in the fall 7Ah cells with a composite of spherical natural graphite coated with A1 and then stabilized with a rigid carbon coating of the disordered nature. Further investigation is needed to fally understand the effect of rigid carbon shell on the electrochemical performance of graphite-based composite materials. 

Regarding their mechanical properties carbon composites can thus be classified as rigid composites [18,19] or soft composites—the carbon pastes - [20]. The composites are also classified by the arrangement of their... 

Figure 34. Comparison of the flexural strengths of unidirectional carbon/carbon composites (left-hand side) with those of hybrid composites in which the final impregnation is made with an epoxy resin (34) The composites were fabricated with high-modulus fibers rigidized with phenolic resin, and subjected to four densification cycles with coal-tar pitch plus sulfur.

Activated carbon fibers (ACFs) offer a choice of other carbon forms for VOC removal. As discussed earlier, the narrow diameter of the fibers provides ready access of adsorptive species to the adsorbent surface. The incorporation of ACF into permeable forms such as felt, paper, and rigid monoliths helps to surmount the disadvantages of using loose fibers. Rigid ACF composites have been prepared at the University of Kentucky and examined for their potential for the removal of low concentrations of VOCs [31]. 

This chapter reports the main features of rigid carbon-polymer composite materials for electrochemical DNA biosensing. Novel approaches based on composites modified with biomolecules (biocomposites) and nanostructured materials (nanocomposites) for the improved biosensing of DNA are also discussed. 

Rigid carbon-polymer composites are obtained by mixing a carbon filler (such as graphite or CNT) with nonconducting polymeric binders (epoxy, methacrylate, silicone, araldite), obtaining a soft paste that becomes rigid after a curing step. 

Pacios, M, de Valle, M., Bartroli,)., and Esplandiu, M.J. (2008) Electrochemical behavior of rigid carbon nanotube composite electrodes. J. Electroanal. Chem., 619-620, 117-124. 

Mendes, R.K., S. Claro-Neto, and E.T.G. Cavalheiro, Evaluation of a new rigid carbon-castor oil polyurethane composite as an electrode material. Talanta, 2002. 57 p. 909-917. 

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