Electrochemical methods to detect specific nucleic acid sequences of hereditary diseases, genetic abnormalities, and viral or bacterial pathogens, are of widespread importance to providing correct medical diagnosis and treatment. We have recently reported two new electrochemical DNA assays. The first exploits a hairpin to duplex transition on a gold electrode. When a complementary DNA target strand binds to the hairpin, the hairpin opens, and the ferrocene redox probe is separated from the electrode affording a decrease in the observed current. Specifically, a 26 base DNA hairpin, containing both a redox active reporter (ferrocene) and terminal thiol functionality for electrochemical gene detection is described. This electrochemical DNA sensor exploits electron-transfer dynamics that alter as a consequence of a large structural rearrangement (hairpin-to-duplex) induced by hybridization of the target DNA sequence.
In the second approach, a simplified “2-piece” reagentless electrochemical assay for DNA detection was constructed. In this design, a conformational change occurs when a surface-immobilized, ferrocene-labeled oligodeoxynucleotide-poly(ethylene glycol) triblock macromolecule binds a target DNA strand. Specifically, the DNA-PEG-DNA macromolecule folds or wraps around the target DNA bringing the ferrocene probe in close proximity to the electrode surface affording an electrochemical response (see figure). These two electrochemical DNA sensors monitor electron-transfer dynamics which are altered as a consequence of a large structural rearrangement induced by hybridization..