Electrochemical impedance detection of DNA hybridization based on the formation of M-DNA on polypyrrole/carbon nanotube modified electrode

A new selective and sensitive biosensing strategy for electrochemical impedance spectroscopy (EIS) measurement of DNA hybridization is described. The detection approach relied on the doping of nucleic acid probes within electropolymerized polypyrrole (PPy) film onto a carboxylic group-functionalized multi-walled carbon nanotubes (MWNTs-COOH) modified electrode and monitoring the impedance changes provoked by the metallation of helix DNA after hybridization. Oligonucleotide probes served as the solo counter anions during the growth of conducting PPy film on the carbon nanotube modified electrode. As a consequence of hybridization and the formation of metallized double-stranded DNA (M-DNA), significant changes in electrochemical impedance values (both in real component Zre and imaginary component Zim) coming from the change of electronic transport resistance of the modified electrode were observed, especially a visible decrease in the Zre. Based on the unique response (delta)Zre after hybridization and metallation at 5469 Hz, only the complementary DNA sequence had an obvious signal of the impedance decrease when compared with 1-base, 3-base mismatched and non-complementary sequences; hybridization amounts of 1-base, 3-base mismatched sequences were obtained only 35.7 and -5.8% responses. The protocol also offered high sensitivity with the detection limitation was 5 ×10^-11 M using 3 S.D., n=11. Results showed that Zn2+-DNA had the best ability to transport electrons in M-DNA double-stranded chains when compared with Co2+-DNA and Ni2+-DNA on the same condition.