Detection of DNA via an ion channel switch biosensor

Detection of DNA by an ion channel switch biosensor has been demonstrated i n a model system, using single-stranded oligonucleotide sequences of 52-84 bases in length. Two different biotinylated probes are bound, via streptavi din, either to the outer region of a gramicidin ion channel dimer or to an immobilized membrane component. The ion channels are switched off upon dete ction of DNA containing complementary epitopes to these probes, separated b y a nonbinding region, at nanomolar levels. The DNA cross-links the ion cha nnel to the immobilized species, preventing ions passing through the channe l. 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 su rface plasmon resonance (BLAcore 2000), and with free energies of dimer for mation for the probes. (C) 2000 Academic Press.