Anomalous Enhancement of Electrochemical Charge Transfer by a Ru Complex Ion Intercalator

We have found that the DNA intercalator [Ru(bpy)(2)DPPZ](2+) (bpy = 2,2'-bipyridine; DPPZ = dipyrido[3,2-a:2',3'-c]phenazine) causes an anomalous increase in charge transfer in electrochemical impedance spectroscopy (EIS). With a carbonaceous electrode and a 1 mM hexacyanoferrate (1 mM [Fe(CN)(6)](3-) and 1 mM [Fe(CN)(6)](4-)) mediator, we found that adding only 1 mu M [Ru(bpy)(2)DPPZ](2+) greatly enhanced the charge transfer between the electrode and hexacyanoferrate mediator, independently of other electrolytes or buffer components. The effect started with a one millionth amount of hexacyanoferrate. Since [Ru(bpy)(2)DPPZ](2+) can intercalate with dsDNA, the effect is highly applicable for dsDNA detection or PCR monitoring. With further developments of this method, EIS sensors not requiring specific electrode modifications should be possible.