Pyrolytic graphite electrodes

FIG. 16 Current versus bias voltage for a CdS nanoparticle on the end of an STM tip. The CdS particles were formed by exposing a bilayer of cadmium arachidate on the STM tip to H2S gas. The other conducting surface is a highly oriented pyrolytic graphite electrode. The inset is a plot of differential conductance versus the bias voltage. (Reproduced with permission from Ref. 202. Copyright 1996 National Academy of Sciences, U. S. A.)... 

Table 1. Linear Ep vs. pH relationships for oxidation of some purines at the stationary pyrolytic graphite electrode...

It has been recently demonstrated that the simplest of the cobalt porphyrins (Co porphine) adsorbed on a pyrolytic graphite electrode is also an efficient electrocatalyst for reduction of 02 into 1120.376 The catalytic activity was attributed to the spontaneous aggregation of the complex on the electrode surface to produce a structure in which the cobalt-cobalt separation is small enough to bridge and activate 02 molecules. The stability of the catalyst is quite poor and largely improved by using porphyrin rings with mew-substitu-tion.377-380 Flowever, as the size of the mew-substituents increases the four-electron reduction efficiency decreases. 

A. Salimi, R.G. Compton, and R. Hallaj, Glucose biosensor prepared by glucose oxidase encapsulated sol-gel and carbon-nanotube-modified basal plane pyrolytic graphite electrode. Anal. Biochem. 333, 49— 56 (2004). 

Biocompatible nanosized polyamidoamine (PAMAM) dendrimer films provided a suitable microenvironment for heme proteins to transfer electron directly with underlying pyrolytic graphite electrodes. The Mb-PAMAM film can catalytically reduced oxygen, hydrogen peroxide, and nitrite, indicating that the potential applicability of the film can be used to fabricate a new type of biosensor or bioreactor based on the direct electron transfer of Mb [234],... 

X.H. Chen, C.M. Ruan, J.L. Kong, and J.Q. Deng, Characterization of the direct electron transfer and bioelectrocatalysis of horseradish peroxidase in DNA film at pyrolytic graphite electrode. Anal. Chim. 

P. Bianco, A. Taye, and J. Haladjian, Incorporation of cytochrome c and cytochrome c3 within poly(ester-sulfonic acid) films cast on pyrolytic graphite electrodes. J. Electroanal. Chem. 377, 299-303 (1994). 

Y. Zhang, P.L. He, and N.F. Hu, Horseradish peroxidase immobilized in Ti02 nanoparticle films on pyrolytic graphite electrodes direct electrochemistry and bioelectrocatalysis. Electrochim. Acta 49, 1981-1988 (2004). 

Dryhurst, G. Electrochemical Oxidation of Biologically-Important Purines at the Pyrolytic Graphite Electrode. Relationship to the Biological Oxidation of Purines. 34, 47-85 (1972). Durr, H. Reactivity of Cycloaikene-carbenes. 40, 103-142 (1973). 

Carbon electrodes can be made from a number of various crystalline forms of carbon. The two most common versions are the carbon paste electrode and the glassy carbon electrode. In Chapter 11, devoted to the electrochemistry of biological functions, it will be seen that pyrolytic graphite electrodes have also found wide application. Recently, attempts to use carbon-nanotube electrodes have been also proposed.9... 

An example is represented by the reduction of cytochrome c using a pyrolytic graphite electrode suitably prepared. In fact, as schematised in Figure 6, this type of carbon material (briefly alluded to in Chapter 3, Section 1.1) has a solid state structure fairly close to the ideal structure of graphite. 

Figure 7 shows the cyclic voltammetric responses of cytochrome c obtained at pyrolytic graphite electrodes treated in various ways. 

It is noted that the glassy carbon electrode behaves as the perpendicularly cut pyrolytic graphite electrode. 

These proteins (FW 11 000) bear a strongly negative charge (-18 in the oxidised state -19 in the reduced state). It is therefore expected that treating a perpendicular pyrolytic graphite electrode with positive additives will afford good results. In effect, under those conditions... 

Figure 24 Square wave voltammograms recorded at an edge-oriented pyrolytic graphite electrode in buffered aqueous solutions of [3Fe-4S] aconitase. (a) pH 6.2 (b) pH 7.5 (c) pH 8.2. Scan rate 0.1 V s ...

It is interesting to note that the plastocyanin from the alga Anabaena variabilis has a similar structure to that isolated from poplar, while having a different amino acid sequence.58 This results in an overall positive charge of +2. Thus, as shown in Figure 32a, it affords a wellshaped response for the Cu(II)/Cu(I) reduction E° = + 0.32 V vs. NHE) using a perpendicular pyrolytic graphite electrode, without the presence of additives. 

Fig. 2.52 Raw square-wave voltammetry data of azurin immobilized on edge plane pyrolytic graphite electrode (PGE) (pH 4.0, 2.0 mol/L NaCl) at different frequencies with = 0.15 V. Dashed line, forward current. Dotted line, backward current. Solid thick line, net current solid thin line, blank net current (reprinted from [101] with permission)...

Fig. 2.63 Voltammetric response of [Ru(bpy)2-PVP] film on pyrolytic graphite electrode recorded at / 5 Hz in 20 mmol/L acetate buffer at pH 5.5 (reprinted from [109] with permission)...

An important example for the snrface catalytic mechanism is the catalytic 0-xidation of DNA at pyrolytic graphite electrode modified with adsorbed poly(4-vinilpyridine) (PVP) with attached Rn(bpy)2 (bpy = 2,2 -bipyridyl) [109]. At low... 

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