Redox enzymes, scanning electrochemical

Topics discussed above are some basic principles and techniques in voltammetry. Voltammetry in the frequency domain where i-E response is obtained at different frequencies from a single experiment known as AC voltammetry or impedance spectroscopy is well established. The use of ultramicroelectrodes in scanning electrochemical microscopy to scan surface redox sites is becoming useful in nanoresearch. There have been extensive efforts made to modify electrodes with enzymes for biosensor development. Wherever an analyte undergoes a redox reaction, voltammetry can be used as the primary sensing technique. Microsensor design and development has recently received... 

Effect of pH. It is expected that the pH of the solution will affect the electrochemical behavior of the PPy-GOD because both the activity and the structure of enzyme GOD are pH dependent. The cyclic voltammetric measurements of the PPy-GOD film electrode were carried out in phosphate buffer solutions of different pHs. The cathodic peak current of the PPy-GOD film was at approximately -380 mV (scan rate 100 mV/s) when pHs of the solution were between 6 and 11. When the pH decreased from 6 to 2, the peak currents of the PPy-GOD film shifted toward a more positive potential. Figure 4 shows the relationship between the cathodic peak potential of the PPy-GOD film and the pH of the solution (curve 1). Curve 2 in Figure 4 shows the relationship between the cathodic peak potential of the PPy-Cl film and the pH. Contrary to the behavior of the PPy-GOD film, the redox potential of the PPy-Cl film was constant in the pH ranging between 2 and 8. 

Figure 4-3. Electrochemical techniques and the redox-linked chemistries of an enzyme film on an electrode. Cyclic voltammetry provides an intuitive map of enzyme activities. A. The non-turnover signal at low scan rates (solid lines) provides thermodynamic information, while raising the scan rate leads to a peak separation (broken lines) the analysis of which gives the rate of interfacial electron exchange and additional information on how this is coupled to chemical reactions. B. Catalysis leads to a continual flow of electrons that amphfles the response and correlates activity with driving force under steady-state conditions here the catalytic current reports on the reduction of an enzyme substrate (sohd hne). Chronoamperometry ahows deconvolution of the potenhal and hme domains here an oxidoreductase is reversibly inactivated by apphcation of the most positive potential, an example is NiFe]-hydrogenase, and inhibition by agent X is shown to be essentially instantaneous.

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