Electrochemical probing of DNA based on oligonucleotide-functionalized polypyrrole

We have developed a new type of electrochemical biosensor based on oligonuc leotide-functionalized polypyrrole. At first, we analyzed the experimental conditions necessary for building such modified electrodes that show a high electroactivity in aqueous media. We developed a precursor polymer bearing an easy leaving ester group on which amino-labeled oligonucleotides with v arious sequence lengths were directly substituted. The electrochemical resp onse of the modified electrode was analyzed in various aqueous media contai ning either complementary or noncomplementary oligonucleotides. Results sho w that the cyclic voltammogram of oligonucleotide-functionalized polypyrrol e is not modified when in the presence of a noncomplementary oligonucleotid e in solution. On the other hand, a significant modification of the voltamm ogram is observed upon addition of a complementary oligonucleotide "target" to the electrolytic medium, which can be quantitatively determined by ampe rometric methods. The detection limit of this electrochemical biosensor is about 10(-11) mol, without any signal processing.