Ultra-Highly Sensitive DNA Detection with Conducting Polymer-Modified Electrodes: Mechanism, Manufacture and Prospects for Rapid e-PCR

Abstract

At low copy number, sequence detection by polymerase chain reaction (PCR) requires up to 30 cycles (amplification 109) to produce a reliably detectable concentration of fluorescently-labelled amplicons. The cycle number and hence detection time is determined by the analytical sensitivity of the detector. Hybridisation of complementary DNA strands to oligonucleotide-modified conducting polymer electrodes yields an increase in the charge transfer resistance for the ferri-ferrocyanide redox couple. We demonstrate sensors using screen-printed carbon electrodes modified with a conducting polymer formed from a monomer pre-functionalised with complementary oligonucleotide, with pM sensitivity for short sequences and aM for bacterial lysate, with a response time-scale of 5 min. The response is due to the variation of electrical resistance within the polymer film. We develop a mechanism based on repulsion from the solution interface of dopant anions by the charge associated with surface-bound DNA. With results for >160 single-use sensors, we formulate a response model based on percolation within a random resistor network and highlight challenges for large-scale manufacture of such sensors. Such sensors used for label-free electrochemical detection for PCR (e-PCR) would decrease the required cycle number from 30 to less than 10 and would offer a much simplified instrument construction.