Use of polymeric indicator for electrochemical DNA sensors: Poly(4-vinylpyridine) derivative bearing [Os(5,6-dimethyl-1,10-phenanthroline)₂Cl]²⁺

A poly(4-vinylpyridine) (PVP) derivative bearing redoxactive osmium complexes, PVP-[Os(5,6-dmphen)₂Cl]²⁺ (5,6-dmphen = 5,6-dimethyl-1,10-phenanthroline), was employed as a hybridization indicator for electrochemical DNA sensors. PVP-[Os(5,6-dmphen)₂Cl] ²⁺ exhibited ∼1000 times higher sensitivity than the corresponding monomeric analogue, [Os(5,6-dmphen)₃]²⁺, in DNA determination due to polymeric effects. The detection limit of the present sensor was ∼0.5 amol. Another merit of the polymeric indicator is that the redox potential was found to be +360 mV (vs Ag/AgCl), which is significantly lower than that reported for the monomeric analogue (+672 mV). The polymeric indicator was applicable to the discrimination of single- and double-base-mismatched DNAs from fully matched target DNA. The polymeric indicator can be removed from the electrode surface by rinsing the electrode in a high-temperature buffer for 6 min, and thus, the polymeric indicator-based DNA sensor can be used repeatedly.