Chemically modified electrodes for NADH oxidation

Gorton and coworkers have been particularly active in this field and produced an excellent review of the methods and approaches used for the successful chemical modification of electrodes for NADH oxidation [33]. They concentrated mainly on the adsorption onto electrode surfaces of mediators which are known to oxidise NADH in solution. The resulting systems were based on phenazines [34], phenoxazines [35, 36] and pheno-thiazines [32]. To date, this approach has produced some of the most successful electrodes for NADH oxidation. However, attempts to use similar mediators attached to poly(siloxane) films at electrode surfaces have proved less successful. Kinetic analysis of the results indicates that this is because of the slow charge transfer between the redox centres within the film so that the catalytic oxidation of NADH is restricted to a thin layer nearest the electrode surface [37, 38]. This illustrates the importance of a charge transfer between mediator groups in polymer modified electrodes. 

Analytical models of modified electrodes for NADH oxidation 

Adsorption onto electrode surface Mediator desorbs from electrode surface with time [35, 36] 

Activate glassy carbon by potential cycling The carbonyl moieties on the electrode surface do not carry out selective oxidation. Intermediates from the oxidation reaction irreversibly inhibit the reaction [19] 

Electrode surface modified by the addition of a polymer containing mediating groups The polymers used are non-conducting, hence, devices suffer from poor charge transport [56] 

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