Carbon electrodes modification

Many applications of modified electrodes with [Ni (cyclam)] + or derivatives have been reported in the past years either on mercury or glassy carbon electrodes Modifications include cubic phases, Langmuir-blodget films, ... 

Figure 10.4 Fabrication and measurements of molecular junction formed on PPF using diazonium chemistry, (a) Cyclic voltammo-gram measured at a PPF electrode featuring an irreversible reduction peak at approximately -0.8V that corresponds to the reduction of diazonium ions with subsequent formation of a C-C with PPF. Growth of the molecular layer results in the increased blocking of electron transfer from the electrode and gradual decrease of the peak intensity (see also Chapter 6 on carbon electrode modification), (b) AFM image of the molecular layer obtained in (a), showing that film is homogeneous, and that the thickness...

Electrochemically assisted modification of carbon electrodes has been accomplished by oxidation of amines (80, 81) and arylacetates (82), reduction of aryl diazonium salts (83), and anodization (oxidation) in a solution with alcohols (75). Of these schemes, reduction of diazonium salts, shown in Figure 8.11, provides a particularly convenient pathway for carbon electrode modification. 

While most amino acids are not electroactive at analytically usable potentials at carbon electrodes, much work is currently directed at general methods of LCEC amino acid detection by electrode surface modification or derivatization of the amino acid. Kok et al. have directly detected amino acids at a copper electrode. Several derivatization methods for amino acids have also been reported 227.228)... 

A qualitatively new approach to the surface pretreatment of solid electrodes is their chemical modification, which means a controlled attachment of suitable redox-active molecules to the electrode surface. The anchored surface molecules act as charge mediators between the elctrode and a substance in the electrolyte. A great effort in this respect was triggered in 1975 when Miller et al. attached the optically active methylester of phenylalanine by covalent bonding to a carbon electrode via the surface oxygen functionalities (cf. Fig. 5.27). Thus prepared, so-called chiral electrode showed stereospecific reduction of 4-acetylpyridine and ethylph-enylglyoxylate (but the product actually contained only a slight excess of one enantiomer). 

SCHEME 4 (a) Carbon fiber microelectrode, and (b) the process of electrode modification. (Reprinted from [158], with permission from Elsevier.)... 

As schematically depicted in Figure 5, two different routes are available for immobilizing biotin-labeled enzymes on the support through avidin-biotin complexation. The first procedure employs the biotin-modified surface on which biotin-labeled enzymes are immobilized through avidin as binder protein. For this procedure, the covalent linkage of biotin onto the surface of a carbon electrode and the preparation of biotin-labeled lipid bilayer on electrode have been studied. An alternative way involves the direct modification of an electrode surface with avidin. If avidin could be immobilized directly without loss of the binding activity to biotin, biotin-labeled enzymes could be loaded more easily on the electrode surface. 

The surface of a carbon electrode was at first coated with a thin film of an anionic polymer such as sodium poly(styrene-sulfonate) 95) or nafion 96) (thickness thousand A) then the cationic Ru(bpy)2+ was adsorbed in the anionic layer electrostatically. The modification was also made by coating water insoluble polymer pendant Ru(bpy)2 + ( ) from its DMF solution 97). These Ru(bpy) +/polymer modified electrode gave a photoresponse in the MV2+ solution with the Pt counter electrode 95-97) The time-current behaviours induced by irradiation and cutoff of the light under argon are shown in Fig. 28. It is interesting to see that the direction of the photocurrent reversed at the electrode potential of ca. 0.4 V (vs. Ag—AgCl) under... 

If the surface of a metal or carbon electrode is covered with a layer of some functional material, the electrode often shows characteristics that are completely different from those of the bare electrode. Electrodes of this sort are generally called modified electrodes [9] and various types have been developed. Some have a mono-molecular layer that is prepared by chemical bonding (chemical modification). Some have a polymer coat that is prepared either by dipping the bare electrode in a solution of the polymer, by evaporating the solvent (ethanol, acetone, etc.) of the polymer solution placed on the electrode surface, or by electrolytic polymerization of the monomer in solution. The polymers of the polymer-modified electrodes are either conducting polymers, redox polymers, or ion-exchange polymers, and can perform various functions. The applications of modified electrodes are really limit-... 

In the previous edition of this book, Dryhurst and McAllister described carbon electrodes in common use at the time, with particular emphasis on fabrication and potential limits [1]. There have been two extensive reviews since the previous edition, one emphasizing electrode kinetics at carbon [2] and one on more general physical and electrochemical properties [3]. In addition to greater popularity of carbon as an electrode, the major developments since 1984 have been an improved understanding of surface properties and structure, and extensive efforts on chemical modification. In the context of electroanalytical applications, the current chapter stresses the relationship between surface structure and reproducibility, plus the variety of carbon materials and pretreatments. Since the intent of the chapter is to guide the reader in using commonly available materials and procedures, many interesting but less common approaches from the literature are not addressed. A particularly active area that is not discussed is the wide variety of carbon electrodes with chemically modified surfaces. 

Electroanalytical sensors based on amperometric measurements at chemically modified electrodes are in the early stages of development. The modes of modification can take many forms, but the most common approach at the present time is the immobilization of ions and molecules in polymer films which are applied to bare metal, semiconductor, and carbon electrodes. Such surface-modified electrodes exhibit unique electrochemical behavior which has been exploited for a variety of 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... 

J. Razumiene, V. Gureviien, A. Vilkanauskyt, L. Marcinkeviien, I. Bach-matova, R. Mekys and V. Laurinaviius, Improvement of screen-printed carbon electrodes by modification with ferrocene derivative, Sens. Actuators B Chem., 95 (2003) 378-383. 

Vakurov et al. [46] evaluated a strategy to improve the covalent binding of AChE to screen-printed carbon electrodes modified with polyamines. To improve the extent of dialdehyde modification, electrodes were aminated. Initially, this was performed by electrochemical reduction of 4-nitrobenzenediazonium to a nitroaryl radical permitting attachment to the carbon surface subsequent reduction of the 4-nitrobenzene yielded a 4-aminobenzene-modified carbon surface. The obtained biosensors resulted in very sensitive devices measuring as low as 10 10 M of OPs. 

McCreery and co-workers have investigated the redox reactions for several redox analytes at glassy carbon electrodes, and have summarized the categorization of redox systems according to the effects of surface modification on electrode kinetics [1-3]. These redox analytes in the present study are known to be sensitive or insensitive to the electronic properties, surface microstructure, and surface termination of the carbon electrodes. 

Guo B, Anzai J, Osa T. Modification of a glassy carbon electrode with diols for the suppression of electrode fouling in biological fluids. Chemical and Pharmaceutical Bulletin (Tokyo) 1996, 44, 860-862. 

Fig. 3.S. Successive differential pulse voltammograms of the glassy carbon electrode with dsDNA adsorbed, immersed in the ssDNA solution during modification s.e. = supporting electrolyte pH 4.5 acetate buffer 0.1 M. Pulse amplitude 50 mV, pulse width 70 ms, scan...

Due to their simplicity of construction, ease of modification, electrical methods of detection, fast response time and the fact that they are the principal structural component of all biomembranes, conventional bilayer lipid membrane (BLM) arises as an ideal system for biosensor technology [88] and they have been studied regarding the possibility of developing DNA biosensors consisting of a glassy carbon electrode-modified by a BLM with incorporated ssDNA [89]. 

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