Ion-channel sensors for electrochemical detection of DNA based on self-assembled PNA monolayers

The gold electrodes modified with self-assembled monolayers composed of a 10-mer peptide nucleic acid (PNA) probe and 8-amino-1-octanethiol were used for the detection of the complementary oligonucleotide with a detection limit of 5.1 x 10(-10) M in a pH 7.0 phosphate buffer solution. In contrast, no response to a non-complementary oligonucleotide was observed. The electrode surface was positively charged in the phosphate buffer solution due to the protonated amine group of the thiol, where the electron transfer reaction between the electroactive marker [Ru(NH3)6]3+ and the electrode was hindered because of the electrostatic repulsion between them. Binding of the complementary oligonucleotide to the PNA probe monolayer cancels the positive charge at the electrode surface, and provides an excess negative charge at the surface, thereby facilitating the access of [Ru(NH3)6]3+ to the electrode surface and its redox reaction.