Abstract
A novel method for the sensitive and specific electrochemical analysis of DNA is described using Faradaic impedance spectroscopy. A thiol−thymine-tagged oligonucleotide (1) capable of forming only one double-stranded turn with the target DNA analyte (2) is assembled on a Au electrode and acts as the sensing interface. The resulting functionalized electrode is reacted with a complex between the target DNA (2) and a biotinylated oligonucleotide (3) to yield a bifunctional double-stranded assembly on the electrode support. The Faradaic impedance spectra, using Fe(CN)63- as redox probe, reveal an increase in the electron-transfer resistance at the electrode surface upon the construction of the double-stranded assembly. This is attributed to the electrostatic repulsion of Fe(CN)63- upon formation of the negatively charged double-stranded superstructure. Binding of an avidin−HRP conjugate to the oligonucleotide−DNA assembly further insulates the electrode and increases the interfacial electron-transfer resistan...
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