Electroactive layers covalent attachment

Figure 4. Schematic representation of a polysiloxane sensing layer covalently attached to a polyHEMA layer, with all electroactive components covalently bound in the sensing membrane.

It is obvious that a PVC membrane can not fulfill the requirement of longterm stability because it can not be linked covalently to the polyHEMA layer and electroactive components or receptor molecules can not be covalently attached. From the work on Ion Selective Electrodes several general features for the design of membrane materials can be defined ... 

The electroactivity of the adsorbed states of this group of compounds is evidently associated with the presence on the adsorbed layer of a pendant functionality which is electroactive in the unadsorbed molecule and is attached to the surface in such a way that the pendant is virtually unperturbed structurally or electronically by the surface. In contrast, a molecule such as hydroquinone which is electroactive prior to adsorption but is strongly perturbed by adsorption (that is, by direct covalent attachment to the Pt surface) is not reversibly electroactive in the adsorbed state (Fig. 26). Accordingly, adsorbed DMBM is reversibly electroactive under almost all conditions, while adsorbed HQ is not reversibly electroactive under any conditions thus far studied. In between these two extremes is THBP, which is reversibly electroactive in one of its adsorbed states but not in the other two. 

A distinctive property of self-doped polymers is their water solubility in the neutral (insulating) and doped (conducting) states. This solubility is due to the covalently attached negatively charged groups on the polymer backbone. Solubility allows a deposition of conductive and electroactive layers onto any, even a nonconducting, surface by a simple casting of self-doped polymers. Such layers could find numerous applications... 

The concept of using the functional groups of electrode surfaces themselves to attach reagents by means of covalent bonding offers synthetic diversity and has been developed for mono- and multi-layer modifications. The electrode surface can be activated by reagents such as organosilanes [5] which can be used to covalently bond electroactive species to the activated electrode surface. Recently, thermally induced free-radical polymerization reactions at the surfaces of silica gel have been demonstrated [21]. This procedure has been applied to Pt and carbon electrode surfaces. These thermally initiated polymer macromolecules have the surface Of the electrode as one of their terminal groups. Preliminary studies indicate that the... 

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