Ligand-modified electrode

Electropolymerization is also an attractive method for the preparation of modified electrodes. In this case it is necessary that the forming film is conductive or permeable for supporting electrolyte and substrates. Film formation of nonelectroactive polymers can proceed until diffusion of electroactive species to the electrode surface becomes negligible. Thus, a variety of nonconducting thin films have been obtained by electrochemical oxidation of aromatic phenols and amines Some of these polymers have ligand properties and can be made electroactive by subsequent inincorporation of transition metal ions... 

Techniques for attaching such ruthenium electrocatalysts to the electrode surface, and thereby realizing some of the advantages of the modified electrode devices, have been developed.512-521 The electrocatalytic activity of these films have been evaluated and some preparative scale experiments performed. The modified electrodes are active and selective catalysts for oxidation of alcohols.5 6-521 However, the kinetics of the catalysis is markedly slower with films compared to bulk solution. This is a consequence of the slowness of the access to highest oxidation states of the complex and of the chemical reactions coupled with the electron transfer in films. In compensation, the stability of catalysts is dramatically improved in films, especially with complexes sensitive to bpy ligand loss like [Ru(bpy)2(0)2]2 + 51, 519 521... 

It would appear certain that the most important need in LCEC is the development of improved electrode materials. It may be possible in the near future to design an electrode that will give superior performance for certain classes of compounds. Modifying electrode surfaces by covalent attachment of various ligands or electron-transfer catalysts (including enzymes) can provide the key to better amperometric devices for all sorts of analytical purposes. Research in the area of chemically modified electrodes (CMEs) has been reviewed (see Chap. 13) [6,11]. Those interested in improving the performance of electrochemical detectors would do well to study these developments in detail. 

Surface complexation — is complexation of metal ions by ligands immobilized on the electrode surface (-> electrode surface area). The ligands may be incorporated in the structure of a -> carbon paste electrode, covalently bound to the surface of a chemically modified electrode (-> surface-modified electrodes), or adsorbed (-> adsorption) on the electrode surface etc. Surface complexation is not confined to electrodes. It can occur on many surfaces, e.g., minerals, when in contact with metal ion solutions or solutions containing complexing ions (in the first case, the surface provides the ligand and the solution the metal ion, whereas in the second case, the surface provides the metal ion and the solution the ligand). Surface complexation can be an important step in the dissolution of solid phases [ii]. 

The preparation of dendrimer biocomposite-modified electrode is the primary step in the development of biosensors. Appropriate strategies have been formulated to prepare stable and highly reproducible dendrimer-modified surfaces. Immobilization of biomolecules like enzymes, proteins and other suitable ligands on the dendrimer-modified electrode with extended lifetime is very important. Some general procedures adopted for the preparation of dendrimer biocomposite-modified surfaces for electrochemical biosensing are described below. Some of the unique procedures developed by various authors are elaborated later during the discussion of the performance of biosensors. 

Takenaka S, Yamashita K, Takagi M, Uto Y, Kondo H (2000) DNA sensing on a DNA probe-modified electrode using ferrocenylnaphthalene diimide as the electrochemically active ligand. Anal Chem 72 1334-1341... 

Electrodes modified by ferrocenyl polymers have been known for a long time.54,61,62 More recently, the Madrid group has extensively studied the derivatization of silylferrocenyl dendrimers.63 Nishihara s group has reported the first example of modified electrodes with AuNPs containing ferrocenyl thiol ligands, in which the stabilization of the modified electrodes is... 

Hydrophobic organic ligands added to a carbon-paste electrode, or immobilized on a chemically modified electrode, can be used for the accumulation of metal ions by the surface-complexation mechanism [89-91], The same goal can be achieved by immobilized ion exchangers such as natural or synthetic zeolites [89], clay minerals [92], silica [93], and ion exchange resins [94] ... 

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