Monitoring the activity of glucose oxidase during the cultivation of Aspergillus niger using novel amperometric sensor with 1, 1′-dimethylferricinium as a mediator

1, 1′-dimethylferricinium (DMF +), a deep blue, and stable mediator, was prepared from a water-soluble 1, 1′-dimethylferrocene(DMF):2-hydroxypropyl-β-cyclodextrin complex via enzymatic oxidation using immobilised bilirubin oxidase. This mediator was superior to other soluble ferrocenes, notably carboxyferrocene, in terms of both solubility (110 mM vs 0·5 mM) and oxidation potential (150 mV vs 300 mV against Ag/AgCl). Although the cyclic voltammogram of DMF + was electrochemically equivalent to DMF, the use of the former resulted in a significantly lower background current (