A competitor-switched electrochemical sensor for detection of DNA

A competitor-switched electrochemical sensor based on a generic displacement strategy was designed for DNA detection. In this strategy, an unmodified single-stranded DNA (cDNA) completely complementary to the target DNA served as the molecular recognition element, while a hairpin DNA (hDNA) labeled with a ferrocene (Fc) and a thiol group at its terminals served as both the competitor element and the probe. This electrochemical sensor was fabricated by self-assembling a dsDNA onto a gold electrode surface. The dsDNA was pre-formed through the hybridization of Fc-labeled hDNA and cDNA with their part complementary sequences. Initially, the labeled ferrocene in the dsDNA was far from surface of the electrode, the electrochemical sensor exhibited a "switch-off" mode due to unfavorable electron transfer of Fc label. However, in the presence of target DNA, cDNA was released from hDNA by target DNA, the hairpin-open hDNA restored its original hairpin structure and the ferrocene approached onto the electrode surface, thus the electrochemical sensor exhibited a "switch-on" mode accompanying with a change in the current response. The experimental results showed that as low as 4.4×10^-10 mol/L target DNA could be distinguishingly detected, and this method had obvious advantages such as facile operation, low cost and reagentless procedure.