Electrochemical detection of a one-base mismatch in an oligonucleotide using ion-channel sensors with self-assembled PNA monolayers

Mixed monolayers of peptide nucleic acid (PNA) and 6-mercapto-1-hexanol on gold disk electrodes were used to detect complementary oligonucleotides at a micromolar level with the ion-channel sensor technique. In contrast, no responses to 100 times more concentrated (i.e., 100 μM) solutions of a one-base mismatch oligonucleotide were observed. Measurements for the mismatch oligonucleotides (dA)₁₀ and (dT)₁₀ provided no responses either. Binding of the complementary oligonucleotide to the PNA probe monolayer increases the negative charge at the surface of the electrode, which results in electrostatic repulsion between the redox marker [Fe(CN)₆](4-/3-) in the solution and the monolayer, thereby hindering the redox reaction of the marker. This allows the indirect detection of the complementary oligonucleotide.