This dissertation describes the hybridization assay on gold electrodes for electrochemical detection of DNA and polymerase chain reaction (PCR) products by means of the electrochemically active compound osmium tetroxide bipyridine. Single base mismatches can be discriminated for their different thermal behavior. We further optimized protective-strand design, surface-probe density, and hybridization temperature. Besides, we also investigated to obtain labeled single stranded DNA targets from asymmetric PCR after labeling forward primer with osmium tetroxide for electrochemical detection.