Evaluation of osmium(II) complexes as mediators accessible for biosensors

Tn order to lower the redox potentials of Os(III)/Os(II) complexes, the mixed ligand complexes of Os(II) were synthesized. The redox potentials of Os(III)/Os(II) complexes could be lowered by the use of 4,4'-dimethyl-2,2'-bipyridine, imidazoles and chloride ion as ligands, e.g., values of the redox potentials of 612 mV vs. Ag/AgCl for [Os(bpy)(3)](3+/2+) (bpy: 2,2'-bipyridine) and -6 mV for [OsCl(Him)(dmbpy)(2)](2+/+) (Him: imidazole, dmbpy: 4,4'-dimethyl-2,2'-bipyridine) were given in 0.1 mol dm(-3) phosphate buffer (pH 7.0). The evaluation of Os(II) complexes as mediators accessible for biosensors was examined according to the determinations of the redox potentials of Os(II) complexes and the second-order rate constants of the reactions as shown in Eqs. (1) and(2). The second-order rate constants for all Os(III) (1) GOx(red) + 2 Os(III) --> GOx(ox) + 2 Os(II) + 2 H+ (GOx: glucose oxidase) (2) HRPox + 2 Os(II) + 2 H+ --> HRPred + 2 Os(III) (HRP: horseradish peroxidase) complexes in Eq. (1) were greater than that for ferrocenecarboxylic acid(FcCOOH). It may be consequently concluded that the mixed ligand complexes of Os(II) were more efficient mediators than FcCOOH for the determination of glucose.