TAML Activator-Based Amperometric Analytical Devices as Alternatives to Peroxidase Biosensors

The ferric TAML catalysts [Fe{C6H2-1,2-(NCOCMe2 NCO)2CMe2}(OH2)]− (1) with counterions Na+ (a) and PPh4 + (b) function similar to horseradish peroxidase in the mediated electron transfer relays, which constitute a basis for amperometric biosensors. The mediators are mono- and bis-cyclometalated Ru and Os compounds of the type of [M(C∼N) x (N∼N)3‑x ] m+ with x = 1 and 2 (N∼N = 2,2′-bipyridine, –C∼N = 2-phenylpyridinato). Cyclic voltammograms of the Ru and Os compounds are not affected by 1a though cathodic currents increase drastically in the presence of hydrogen peroxide. The reduction potentials of [M(C∼N) x (N∼N)3‑x ] m+ complexes vary with both the nature of metal (Ru or Os) and the number of cyclometalated ligands x (1 or 2) and therefore the potential of working electrode can be set in the range of from −0.1 to +0.6 V versus the normal hydrogen electrode (NHE). A prototype of a biosensor for H2O2 is described, in which the 1b catalyst and [Os(C∼N)2(N∼N)]+ mediator were coimmobilized on the surface of the glassy carbon electrode using a polymeric coating.