Electrode CPE

CNT randomly dispersed composites Many soft and rigid composites of carbon nanotubes have been reported [17]. The first carbon-nanotube-modified electrode was made from a carbon-nanotube paste using bromoform as an organic binder (though other binders are currently used for the paste formation, i.e. mineral oil) [105]. In this first application, the electrochemistry of dopamine was proved and a reversible behavior was found to occur at low potentials with rates of electron transfer much faster than those observed for graphite electrodes. Carbon-nanotube paste electrodes share the advantages of the classical carbon paste electrode (CPE) such as the feasibility to incorporate different substances, low background current, chemical inertness and an easy renewal nature [106,107]. The added value with CNTs comes from the enhancement of the electron-transfer reactions due to the already discussed mechanisms. 

Electrode materials Pt. platinum PG. pyrographite AC, active carbon GC. glasslike carbon CF. carbon fiber. CCEs, ceramic carbon electrodes CPE. carbon (graphite) paste electrode Soim e-. Refs. 12, 201. and 206-221... 

The use of a carbon paste electrode (CPE) incorporating tyrosinase (see Section VI.A.2) as ELD for LC determination of phenols was investigated. The enzyme-modified electrode showed higher stability than the unmodified one °. ... 

A PCR sequence was used related to Hepatitis B (HBV) virus genome. Optimization of hybridization detection was performed with 17-mer short oligonucleotides. Carbon paste electrodes (CPE) and hanging mercury drop electrodes (HMDE) were used as sensor surface, CV and DPV transduction of MDB accumulated after hybridization between 23-mer capture probe and HBV-PCR amplicon was monitored for the detection. By using MDB indicator. Herpes simplex (HSV) virus genome detection and discrimination of HSV type I and type II viruses were performed in PCR amplicon... 

Liu and coworkers utilized Hb adsorbed on colloidal gold nanoparticles in carbon paste electrode (CPE) to investigate the reduction of nitrite at pH 4. (One criticism of this work is that, at this low pH, aqueous Hb is denatured. 

When going back to the classification of carbon pastes and the respective electrodes, the term carbon paste electrode (CPE) means a setup of carbon paste fixed in a suitable body, which may be of quite different construction (see, e.g., [1, 2, 26, 46-49] and many others in [5]) nevertheless, only exceptionally being reflected In naming of the electrode Itself. Historically, some of the first definitions had classified CPEs as a special type of solid carbon electrode [2, 7], later taxonomy preferred the classification among heterogeneous carbon electrodes [4, 8, 9]. Finally, there were also other ways to classify or sort carbon pastes and the... 

At carbon electrodes, purine bases produce well-defined oxidation peaks within a wide pH range (0-12.5) [142,143]. Purine nucleosides and nucleotides are oxidized at potentials more positive than the parent bases [144]. Signals corresponding to the oxidation of purine bases, nucleotides, and nucleotides have also been obtained using chemically modified carbon electrodes [145,146] (for more details see Sect. 12.4.3). Recently, Cai and coworkers [147] proposed a method for trace A determination using an electrochemically/chemically modified (in alkahne sodium nitrate solution) carbon paste electrode (CPE). Pyrimidines are considered to be electroinactive on carbon electrodes however, Oliveira-Brett and Matysik recently reported [148] specific anodic peaks observed in solutions of T and C bases (but not their nucleosides). Sugar components of nucleotides can be oxidized at copper electrodes [149]. 

A more relevant example is related to the charge transfer at an electrode, which is in contact with a liquid solution. This situation is best described by a parallel combination of a resistance and a capacitance (circuit 2), where the resistance conveys the charge transfer kinetics at the electrode/liquid interface and the capacitance reflects the accumulation of charge at the Helmholtz layer (Helmholtz capacitance). A series resistance (denoted here by R2) associated to this RC combination reflects the Ohmic losses. This equivalent circuit is called a Randles circuit. On the other hand, if the relevant capacitive processes identifled in the electrochemical response of the system are not ideal, which is often the case for porous electrodes, CPEs (Q) can replace the capacitances (circuit 3). The parameter accounting for the nonideality of the system (n) must be comprised between 0.8 and 1 (to model a nonideal capacitance). Otherwise, for < 0.8, the CPE can be related to a different process, which is not essentially capacitive. It is this circuit that is most commonly used to describe charge transfer... 

A modified carbon paste electrode (CPE) using asolectin, cytochrome c, and cytochrome oxidase were applied for amperometric determination of cyanide [56]. The modified CP matrix mimics a biological membrane environment. The sensor, polarized at —0.15 V versus Ag/AgCl, generates the reduced form of cytochrome c, which in turn is oxidized by the enzyme cytochrome oxidase. The resulting current is related to the enzyme activity and is depressed by inhibitors of cytochrome oxidase such as cyanide. Concentrations of cyanide as low as 0.5 pM can be measured with half-maximal response at about 12 pM. The inhibition is reversible and reproducible (RSD = 4%), allowing cyanide determination for more than 2 months using the same probe. Possible use of this biosensor in flow systems was illustrated. 

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