Echinomycin and cobalt-phenanthroline as redox indicators of DNA hybridization at gold electrodes.

A bis-intercalator echinomycin (ECHI) and a simple intercalator [Co(phen)3]3+ were used as a novel electrochemical redox indicators to detect DNA hybridization at gold electrodes (AuE). In order to minimize the nonspecific adsorption of oligonucleotides (ODN), the thiol-derivatized oligonucleotides were immobilized onto AuE in the first step, and the exposition of AuE to 6-mercapto-1-hexanol (MCH) followed in the second step of this procedure. In this arrangement good reproducibility and discrimination between single-stranded (ss) probe and double-stranded (ds) hybrid DNA were obtained. While both redox indicators showed a good ability to discriminate between the ss probe and ds hybrid DNA, the signals of ECHI were by an order of maginitude higher than those of [Co(phen)3]3+ in a good agreement with stronger DNA binding by the bis-intercalator as compared to the simple intercalator. In addition, DNA single-base mismatch (DNA point mutation) was easily detected by means of ECHI.