Using the redox-active DNA conjugate (ferrocene-modified oligonucleotide 12 mer) as a probe, the novel electrochemical gene sensor, which is sensitive, convenient, and not relying on radio isotope, has been developed. Oligonucleotide (16 met) complementary to the target (19 met) was immobilized onto gold electrode through the specific chemisorption of successive phosphorothioates which were introduced into 5′-end of the oligonucleotide. The sequence of the conjugate was designed to be also complementary to another site of the target. Therefore, the conjugate and the oligonucleotide anchoring on the electrode formed a sandwich-type ternary complex with a target DNA to give electric currents based on the ferrocene oxidation. By using this system, we have distinguished the mutant that has one base substitution from the fully complementary target.
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