Figure 6 An ion-channel sensor based on a PNA probe immobilized on gold electrode, and detection of the hybridization based on the electrostatic repulsion of a negatively charged redox marker (shown as an octahedron). (From Ref. 32.)

Over the past 10 years, we have witnessed a tremendous progress toward the development of electrochemical DNA biosensors. Such devices are of considerable recent interest due to their extraordinary promise for obtaining sequence-specific information in a faster, simpler, and cheaper manner compared to traditional hybridization assays. In addition to excellent economic prospects, such devices offer innovative routes for interfacing (at the molecular level) the DNA-recognition and signaltransduction elements, i.e., an exciting opportunity for basic research. The realization of instant on-site (clinical, forensic, or environmental) DNA testing would require additional developmental work. Particular attention should be given to the integration of various processes, including sample collection, DNA extraction and amplification, with the actual hybridization detection, on a single microfabricated chip. By performing all the steps of the biological assay on a microchip platform, we expect significant advantages in terms of cost, speed, simplicity, and automation. The integration of multiple biosensors in connection to DNA microarrays should lead to the simultaneous analysis of multiple DNA sequences, and hence to the generation of characteristic hybridization patterns and acquisition of expression information. Screening of DNA-protein or DNA-drug interactions would also benefit from such DNA microarrays. New DNA biosensor technologies are anticipated in the near future in response to the above opportunities.