Detection of interleukin-8 mRNA using a gold nanowire-based biosensor with a stem-loop probe

We report a signal–off, electrochemical DNA (E–DNA) sensor for detection of salivary mRNA employing a stem–loop probe. One end of a stem–loop DNA is immobilised onto a gold electrode via a terminal thiol modification (forming a self assembled monolayer) with the other end bearing a redox–reporting methylene blue to create an E–DNA sensor. In the absence of target, the stem structure of the probe DNA holds the redox tag in proximity to the electrode, producing a large faradaic current. Hybridisation to a complementary oligonucleotide removes the redox tag from the electrode, significantly decreasing this current and supporting the ready detection of specific DNA sequences. The observed signal gain is sufficient to achieve a demonstrated detection limit of 200 pM, which is among the best reported for signal–off electrochemical DNA detection. This suggests that E–DNA signalling arises from binding–linked changes.