Electrochemical probing of DNA based on oligonucleotide-functionalized polypyrrole

We have developed a new type of electrochemical biosensor based on oligonucleotide-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 various sequence lengths were directly substituted. The electrochemical response of the modified electrode was analyzed in various aqueous media containing either complementary or noncomplementary oligonucleotides. Results show that the cyclic voltammogram of oligonucleotide-functionalized polypyrrole is not modified when in the presence of a noncomplementary oligonucleotide in solution. On the other hand, a significant modification of the voltammogram is observed upon addition of a complementary oligonucleotide "target" to the electrolytic medium, which can be quantitatively determined by amperometric methods. The detection limit of this electrochemical biosensor is about 10(-11) mol, without any signal processing.