Electroactive mediators

In initial ET rate measurements, both the NB and aqueous phases contained 0.1 M TEAP, enabling measurements to be made with a constant Galvani potential difference across the liquid junction. In these early studies, the concentration of Fc used in the organic phase (phase 2) was at least 50 times the concentration of the electroactive mediator in the aqueous phase which contained the probe UME (phase 1). This ensured that the interfacial process was not limited by mass transport in the organic phase, and that the simple constant-composition model, described briefly in Section IV, could be used. 

In an ideal case the electroactive mediator is attached in a monolayer coverage to a flat surface. The immobilized redox couple shows a significantly different electrochemical behaviour in comparison with that transported to the electrode by diffusion from the electrolyte. For instance, the reversible charge transfer reaction of an immobilized mediator is characterized by a symmetrical cyclic voltammogram ( pc - Epa = 0 jpa = —jpc= /p ) depicted in Fig. 5.31. The peak current density, p, is directly proportional to the potential sweep rate, v ... 

Figure 4-13 Scheme showing the use of electroactive mediator in the design of an amperometric enz/me electrode.The mediator accepts electi ons directly from the enzyme, and is oxidized at the surface of the working electrode, creating more oxidized mediator to continue this process. (From D Orazio P. It) Lewendrowski, K, ed. Oinica chemistry laboratory management and clinical correlations, Philadelphia Lippincott, Williams and Wilkins, 2002 464.)... 

The measurement of oxygen evolution using a Clark-type oxygen electrode is a standard procedure in the field of photosynthesis research. The measure is simple and the oxygen electrode constitutes an interesting method to evaluate the photosynthetic activity. Several types of photosystem II specific artificial electron acceptors can be used as electroactive mediators to maximize the photosynthetic activity. The more used mediator is potassium ferricyanide " but this one... 

Electrochemical DNA biosensors offer sensitivity, selectivity, and low-cost detection in this field therefore, numerous voltammetric approaches have been developed containing direct electrochemistry of DNA bases and electrochemistry of DNA-specific electroactive mediators (reporters) [24,25]. 

In this report, we demonstrate that oxygen can serve as an electroactive mediator through a Mehler type reaction. It is shown that the photocurrent is produced by the oxidation of H2O2 at the platinum electrode. 

SECM is a technique utilized to measure localized electroactive analytes and the topography of a surface by applying the measured current to the feedback system. A typical SECM setup utilizes an ultramicroelectrode (UME) to measure the faradaic current produced from the reduction/oxidation of an electroactive mediator within the solution surrounding the sample of interest. For a more in-depth discussion on SECM details and studies, please refer to Amemiya and coworkers review in Chapter 18 this review will focus only on the application of nanopores to SECM studies. 

FIGURE 13.9 Schematic illustrating SECMIT Species A is the common electroactive mediator in the two phases while B denotes the product of the electrode reaction. Electrochemical removal of A in phase 1 induces transfer of A from phase 2 to 1. Z) denotes diffusion coefficient. (Adapted from Gonsalves, M. et al., Biophys. J., 78, 1578, 2000.)... 

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