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

Abstract

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 μM [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.

Electrochemical Impedimetric Real-Time Polymerase Chain Reactions Using Anomalous Charge Transfer Enhancement

“…We focused on this [Ru­(bpy) 2 DPPZ] 2+ and investigated its electrochemical properties using a three-electrode system (glassy carbon (GC) working electrode (WE), Pt wire counter electrode (CE), and Ag/AgCl reference electrode) in order to construct a new electrochemical detection system. During the course of the study, we found that a small amount of [Ru­(bpy) 2 DPPZ] 2+ greatly enhanced the charge transfer between a carbon electrode and hexacyanoferrate mediators (named, Ru effect) . Further detailed investigation revealed that this effect was caused by [Fe­(CN) 6 ] 3–/4– , [Ru­(bpy) 2 DPPZ] 2+ , and a carbon electrode, and it was independent of other agents in the solution.…”

“…Addition of 1.0 μM [Ru­(bpy) 2 DPPZ] 2+ made the Rct further decrease to 450 Ω, 1/6 of the original value (Figure iii). This Ru effect was observed from 1 nM to 1 mM [Ru­(bpy) 2 DPPZ] 2+ concentrations when 1 mM [Fe­(CN) 6 ] 3–/4– was used, and various kinds of carbonaceous electrodes showed this Ru effect …”

“…In this letter, we present a new electrochemical impedimetric PCR detection method based on our discovery that electrochemical charge transfer between [Fe(CN) 6 ] 3−/4− mediators and a carbon electrode is greatly enhanced by a small amount of [Ru(bpy) 2 DPPZ] 2+ intercalators. 40 The scheme of the proposed PCR method is shown in Figure 1. The carbon electrode is protected by a poly(vinyl alcohol) (PVA) layer.…”

“…During the course of the study, we found that a small amount of [Ru(bpy) 2 DPPZ] 2+ greatly enhanced the charge transfer between a carbon electrode and hexacyanoferrate mediators (named, Ru effect). 40 Further detailed investigation revealed that this effect was caused by [Fe(CN) 6 ] 3−/4− , [Ru-(bpy) 2 DPPZ] 2+ , and a carbon electrode, and it was independent of other agents in the solution.…”

“…This Ru effect was observed from 1 nM to 1 mM [Ru(bpy) 2 DPPZ] 2+ concentrations when 1 mM [Fe(CN) 6 ] 3−/4− was used, and various kinds of carbonaceous electrodes showed this Ru effect. 40 Furthermore, as ssDNA (17 nt) and dsDNA (60 bp) were added to the solution, the GC WE nonspecifically adsorbed these DNA molecules, resulting in an increase in Rct (Figure 2iv, v). The Rct transient response is shown in Figure S2.…”