Detection of DNA via an ion channel switch biosensor

Detection of DNA by an ion channel switch biosensor has been demonstrated in a model system, using single-stranded oligonucleotide sequences of 52-84 bases in length. Two different biotinylated probes are bound, via streptavidin, either to the outer region of a gramicidin ion channel dimer or to an immobilized membrane component. The ion channels are switched off upon detection of DNA containing complementary epitopes to these probes, separated by a nonbinding region, at nanomolar levels. The DNA cross-links the ion channel to the immobilized species, preventing ions passing through the channel. Addition of DNase I after the target DNA has been added switches the ion channels on. The DNA response is dependent on the rate of hybridization of the individual probes to their complementary epitopes, as shown by using a single probe against DNA containing a repeat of the complementary epitope. These results were correlated with hybridization rates determined using surface plasmon resonance (BIAcore 2000), and with free energies of dimer formation for the probes.