Generation/collection mode immobilized enzymes

A feature of SECM is the quantitative theory available based on reaction-diffusion models (Chapter 5). The SECM may be used for kinetic studies in either the feedback or generation-collection modes. These two possibilities are described below from the point of view of studying immobilized enzyme kinetics. 

Zhao and Wittstock [19] conducted a comparative investigation of the kinetics of PQQ-dependent glucose dehydrogenase in the feedback and the generation-collection mode. The experiment was performed under conditions such that zero-order kinetics with respect to glucose and first-order kinetics with respect to the different mediators were maintained. This enzyme showed much faster kinetics than GOx despite some activity loss during immobilization. 

GC mode experiments have been applied to the study of immobilized oxi-doreductases such as diaphorase and the glucose oxidase/glucose system (15,21), which has also been investigated by feedback with ferrocenyl mediators (10). In the feedback experiment, the catalytic cycle of the enzyme is dependent on ferrocenium species generated at the tip, as described in Sec. I.C. A generation-collection experiment utilizes a bulk solution concentration of the oxidized mediator, and the tip is poised at a potential sufficiently positive to detect ferrocene, or another reaction product such as H202, present near the interface (Fig. 6). The enzymatic reaction therefore occurs over the whole specimen, wherever there is active enzyme and a supply of substrate. In the feedback experiment, the tip current includes the flux of mediator from bulk solution as well as the flux of reduced mediator due to... 

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