Indicator Free DNA Hybridization Detection by Impedance Measurement Based on the DNA‐Doped Conducting Polymer Film Formed on the Carbon Nanotube Modified Electrode

Abstract

A new biosensing strategy for direct electrochemical detection of DNA hybridization by AC impedance measurement is described. The indicator or label free approach was developed on the basis of the carbon nanotubes coupled with a conductive polymer polypyrrole (PPy). Multi-walled carbon nanotubes functionalized with carboxylic group (MWNTs-COOH) were modified on the glassy carbon electrode (GCE) and the oligonucleotide probes were doped within the electro-polymerized PPy films by serving as the sole counter anion during the growth of the conducting films. Before and after hybridization reaction with the complementary DNA sequences, a decrease of impedance values was observed as a result of the reduction of the electrode resistance. Hybridization amounts of the one-base, two-base and three-base mismatched sequences were obtained only in a 51%, 18% and 8.2% response when compared to that for the complementary matched sequence. Such unique response is attributed to the concomitant conductivity changes of the PPy-polymerized carbon nanotubes, and offers great promise for reagentless DNA hybridization analysis.

Configuration and capacitance properties of polypyrrole/aligned carbon nanotubes synthesized by electropolymerization

“…During the electropolymerization process, individual nanotubes in the ACNTs acted as electronic wires, transferring electrons from the bottom of the electrode to the outmost end of the ACNTs, displaying similar polymerization behavior to that of a GCE modified with entangled MWCNTs [33]. Because of the catalyzing properties of CNTs, the observed oxidization potential of pyrrole was lower than that on GCE (0.65 V), and was similar to that found on a GCE modified with entangled MWCNTs (0.5 V) [34]. Therefore, the polymerization of pyrrole on ACNTs can be described as follows: when the potential reached 0.5 V (vs. Ag/AgCl), pyrrole monomers surrounding the walls of the ACNTs were oxidized into free radicals.…”

“…The already formed PPy-coated ACNTs would self-catalyze electropolymerization, thus explaining the observed increase in the electropolymerization current during polymerization. The phenomenon of PPy-coated CNTs self-catalyzing PPy electropolymerization was also observed for electropolymerization of PPy onto MWCNTs [34,35]. In addition, because ACNTs provide a large specific surface area for PPy to cover, a large electropolymerization current is generated and the polymerization of PPy onto the ACNT electrode is continuous.…”

“…In addition, because ACNTs provide a large specific surface area for PPy to cover, a large electropolymerization current is generated and the polymerization of PPy onto the ACNT electrode is continuous. In the experiments, the electropolymerization current generated on the ACNTmodified electrode was 17 times that on a bare GCE for the same polymerization cycle [34], and electropolymerization of PPy occurred even after 100 cycles. In contrast, on a traditional GCE electrode, electropolymerization only occurred for around 5 cycles, and then the electropolymerization current stopped increasing [35].…”

Biosensors and Their Principles

“…[26,54] DNA detection sensitivity of biosensor which is modified with CNT is much higher than conventional DNA sensors [26,55].…”

Detection of Sequence-Specific Gene by Multi-Channel Electrochemical DNA Chips

“…From this curve a much larger R et value than that from curve a is obtained owing to much more negative charges of the backbone of pDNA, which blocks the interfacial electron transfer of [Fe(CN) 6 ] 3−/4− . 10,14,31 After the pDNA1/Au was treated with MCH, the Nyquist diagram is shown as curve c. The R et value from this curve decreases dramatically compared with that from curve b, indicating that negative charges of the MCH monolayer are less than that compact DNA layer. The Nyquist diagram of MCH+ dsDNA/Au is shown as curve d. It can be seen that the R et value increases obviously compared with that from curve c, suggesting the increase of DNA by hybridization.…”