Electrocatalytic detection, analytes

Selected PMEs shown to be useful in the electrocatalytically detecting analytes are discussed in the following paragraphs. 

Figure 26.8 shows the scheme of the genosensor device and the analytical signals obtained with electrocatalytic detection (Fig. 26.8A) and enzymatic detection (Fig. 26.8B). 

Coupled reactions of two or more enzymes can also be used to minimize interference, as well as to amplify the response and extend the scope of the enzyme electrode towards additional analytes. For example, peroxidases can be coupled with oxidases to allow low-potential detection of the liberated peroxide. Electrocatalytic surfaces, particularly those based on metallized carbon, represent a new and effective approach for minimizing electroactive interference [9]. Such strategy relies on the preferential electrocatalytic detection of the liberated peroxide or NADH species at rhodium or ruthenium dispersed carbon bioelectrodes. 

Electrochemical sensor fabrication has dominated the analytical application of polymers. In some sensors the polymer film acts as a membrane for the preconcentration of ions or elements before electrochemical detection. Polymers also serve as materials for electrode modification that lower the potential for detecting analytes. In addition, some polymer films function as electrocatalytic surfaces. Using a polymer in biosensors is a very rapidly developing area of electroanalytical chemistry. Polymeric matrix modifiers have been applied as diffusional barriers in constructing not only sensitive amperometric biosensors, but also electrochemical sensors that apply potentiometric, conductimetric, optical, and gas-sensing transducer systems. The principles, operations, and application of potentiometric, conductimetric, optical and gas sensors are described in Refs. 13, 39-41. In this chapter, we focus mainly on amperometric biosensors based on redox enzymes. 

Table 5.4 Nonexhaustive list of different metal NPs deposited on BDD electrodes for the electrocatalytic detection of a range of different analytes.

The following brief review of electrocatalytic detection mechanisms at noble metal electrodes and fundamental theory of PED has been designed to help the reader understand and explore the breadth and analytical utility of PED techniques for carbohydrates in food and beverage analysis. 

The three steps (1) electrocatalytic oxidation for detection, (2) oxide formation to clean the electrode surface, and (3) oxide removal to reactivate the electrode and preadsorb analyte for the next cycle form the basis of all PED techniques. Three modes of anodic electrocatalytic detection can occur at noble metal electrodes. 

Fig. 26.8. Schematic representation of the analytical procedure followed for the construction of the genosensor and the detection of a complementary target and a single-base mismatch target. (A) Electrocatalytic and (B) enzymatic detection.

Casclla, LG., Cataldi, T.R.L, Salvi, A.M., and Desimoni, E. 1993. Electrocatalytic oxidation and liquid chromatographic detection of aliphatic alcohols at a nickel-based glassy carbon modified electrode. Analytical Chemistry 65, 3143-3150. 

Domenech, A., and Alarcon, J. 2007. Microheterogeneous electrocatalytic chiral recognition at monoclinic vanadium-doped zirconias Enantioselective detection of glucose. Analytical Chemistry 79, 6742-6751. 

Several metal oxides (platinum, gold," nickel, copper, ) and cobalt phtalo-cyanine have been employed as surface bound mediators for carbohydrate detection. In a dc amperometric mode of operation detectors based on these mediators exhibit a significant loss of response with time and/or exposure to analyte. Various potential pulse programs have circumvented this stability problem, but at the expense of sensitivity and complexity of the instrumentation. Silver electrodes coated with electrogenerated silver oxide exhibit electrocatalytic activity with respect to carbohydrate oxidation. This paper describes our efforts to utilize an electrode as a carbohydrate detector in a dc amperometric mode. 

The analytical application of particle-dispersed-modified electrodes to the selective detection of a single analyte is limited because of broad catalytic activities thus their use as electrochemical detectors following chromatographic separation of carbohydrates is often suggested. Similar nonspecific catalytic PMEs consisting of electrocatalytic RUO2 particles and Ru(OH2)6 in Nafion have been shown to catalyze the oxidation of catechol and of alcohols, respectively these could presumably be used in place of the carbon paste Ru02-modified electrode developed for postseparation detection of carbohydrates and alcohols. Other electrocatalytic particle electrodes were prepared from lead dioxide in polypyrrole and CoPc entrapped behind a permselective cellulose acetate film. ... 

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