Dipolar ruthenium-ammine complexes with 4,4′-bipyridinium ions accessible for both amperometric and colorimetric glucose sensors

Dipolar ruthenium-ammine complexes [Ru(NH3)5(L+)]4+/3+ (L+ = 4,4′-bipyridinium ions) possess the low redox potentials of 0.15–0.18 V vs. Ag/AgCl and the great rate constants of 5.7 × 106–1.7 × 107 M−1 s−1 for the electron-transfer reactions between the reduced form of glucose oxidase and [Ru(NH3)5(L+)]4+. The color immediately changes from colorless to blue when glucose is added to an aqueous mixture containing [Ru(NH3)5(L+)]4+ and the oxidized form of glucose oxidase. These dipolar ruthenium-ammine complexes are concluded to be useful for both amperometric and colorimetric glucose sensors.