Flow detection of nucleic acids at a conducting polymer-modified electrode

A new protocol for electrochemical detection of nucleic acids, based on polypyrrole (PPy)-coated electrodes, is demonstrated using flow injection analysis. The conducting polymer detection scheme offers a fast, sensitive, universal detection of oligonucleotides, DNA, and RNA. The response is attributed to the adsorption/desorption of the nucleic acids onto the Pgi film during the passage of the sample plug over the coated electrode. The influence of various experimental parameters of the film preparation and the electrochemical detection has been investigated. Optimal performance has been achieved using the nitrate film dopant, a detection potential of -0.15 V (vs Ag/AgCl), and a flow rate of 0.6 mL/min. Good linearity and reproducibility (RSD = 2.1%) are observed, along with very low detection limits (e.g., 6.1 x 10(-16) mol of dsDNA in the 20-mu L samples). Compared to common detectors based on the electroactivity of DNA, the conducting polymer detection scheme is not limited to purine-containing nucleic acids or to a strongly alkaline media and is less susceptible to interferences from easily oxidizable species (e.g., ascorbic acid). The attractive behavior of the PPy now detector holds great promise for monitoring nucleic acids in other now systems, microscale separations, and on-chip platforms.