Direct electron transfer of HRP

CV measurements of the modified brushes showed the typical electrochemical response corresponding to a surface-confined electroactive species and the redox counterions, as ferriq anide species form stable ion pairs with the quaternary ammonium groups of the brush (Fig. 4.6] [47]. In a noncovalent way, Mao et al. have reported that ILs could be directly immobilized on the glassy carbon electrode (GC] by casting and observed the electrocatalytic activity toward ascorbic acid (AA] and the capability to facilitate direct electron transfer of horseradish peroxidase (HRP] (Fig. 4.7]... 

First examples of the amperometric detection of H202 accomplished in such a range were based on the use of an enzyme, namely horseradish peroxidase (HRP), a prototypical hemeprotein peroxidase, which catalyses the reduction of H202 and due to its peculiar structure, allows direct electron transfer between its active site and the electrode surface at low applied potential [14 17]. This approach, although it shows good sensitivity and accuracy, suffers from some important shortcomings such as low stability and the limited binding of HRP to solid surfaces. 

Gold nanoparticles have been used to immobilize micro-peroxidase 11,46 tyrosinase,47 and hemoglobin48 to construct amperometric sensors, while silver nanoparticles have been used to enhance electron transfer of cytochrome c and myoglobin onto pyrolitic graphite electrodes.49 The use of semiconductor and oxide nanoparticles has also been reported, such as horseradish peroxidase (HRP) on TiC>2 nanoparticles,50 as well as Fe304 and MnC>4 nanoparticles to immobilize and facilitate direct electron transfer.51... 

Immobilization of nanoparticles and enzymes onto electrode surfaces using various entrapment chemistries, that is, sol-gels, layered polyions, and hydrogels, has allowed for greater functionality and improved stability. Crumbliss and coworkers demonstrated the direct electron transfer between the redox center of HRP by evaporation... 

Figure 1. The direct, non-mediated electrical contacting of enzymes (A) direct electron transfer between an electrode and an enzyme molecule located in close vicinity to the surface (B) application of the direct electrical wiring of HRP for the detection of H2O2 produced by an oxidase in response to a primary substrate.

The direct electron-transfer communication between HRP and electrodes allows the electroreduction of H2O2 in the potential range —0.2 to 0 V (vs. SCE) and its coupling to these oxidases can thus yield amperometric biosensors (Figure 1B). The... 

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