Modification of Carbon Electrode Surfaces

Muhammad Tanzirul Alam andJ. Justin Gooding 

Edited by Richard C. Alkire, Philip N. Bartlett and Jacek Lipkowski. 

Modification procedures for carbon electrodes are quite diverse. For convenience, in this chapter, they are broadly divided into two parts covalent and non-covalent modifications. It is worth mentioning that this chapter is not intended to cover the entire hterature on carbon modification, instead the focus is given on basic features of each process of modification and how it changes the nature of carbon electrode surfaces. From the wide variety of applications of modified electrodes, a few selected articles are discussed in short at the end of each modification process to demonstrate its utility. 

---

Although silane chemistry provides a very versatile method for modification of carbon electrode surfaces, it is difficult to obtain ordered layers with well-defined thickness (see Figure 8.10). Moreover, these layers show poor reproducibihty and stability, and thus far have mainly been used in fundamental studies (43). 

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. 

Another method for the modification of carbon electrodes with macrocycles towards the electroreduction of CO2 is to form chemical bonds between the electrode and the macrocycle. Several studies have shown that it is possible to attach small organic molecules, to the polished gassy carbon surface and then this attached molecule could be an anchor for another molecule, in this case Coporphyrins or Co-phthalocyanine ... 

Among the carbon-based electrodes, used to replace the mercury electrode, modification of the electrode surface to improve its performance was made by the addition of carbon nanotubes, magnetic or metallic nanoparticles, thin films, etc. The literature reports the use of biosensors incorporating tyrosinase (polyphenol oxidase) for the detection of phenols in aqueous and in organic medium. 

Electrode material and surface state have a considerable effect on the electrochemical reaction that could detect Sulfur Mustard hence, modification of the electrode surface is the only way to obtain the electrochemical activity from blister agents. By selecting a carbon material, selectivity and sensitivity of the gas are controlled using its surface properties. A compact type of electrochemical sensor to detect blister agents, such as Sulfur Mustard or Lewisite 1,... 

A. Vakurov, C.E. Simpson, C.L. Daly, T.D. Gibson, and P.A. Millner, Acetylcholinesterase-based biosensor electrodes for organophosphate pesticide detection I. Modification of carbon surface for immobilization of acetylcholinesterase. Biosens. Bioelectron. 20, 1118-1125 (2004). 

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. 

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... 

---