Chemical control of electrode functionalization for detection of DNA hybridization by electrochemical impedance spectroscopy.

We report sensitive label-free detection of DNA oligonucleotide sequences using ac impedance measurements. The surface attachment chemistry is critical, and using mixed self-assembled monolayers on a gold electrode results in much better performance than homogeneous self-assembled monolayers. Contrary to expectations, binding of the target sequence reduces rather than increases the charge transfer resistance. Similar behavior is observed on indium tin oxide electrodes, and we ascribe it to the hydrophilicity and rigidity of the DNA duplex that cause it to reside further from the electrode surface and facilitate the approach of negatively charged redox moieties to the interface.