We describe a platform for sequence-specific nucleic acid (NA) detection utilizing a micropipet tapered to a 2 mu m diameter pore and 3 mu m diameter polystyrene beads to which uncharged peptide nucleic acid (PNA) probe molecules have been conjugated. As the target NAs hybridize to the complementary PNA-beads, the beads acquire negative charge and become electrophoretically mobile. An applied electric field guides these NA-PNA-beads toward the pipet tip, which they obstruct, leading to an indefinite, electrically detectable, partial blockade of the pore. In the presence of noncomplementary NA, even to the level of single base mismatch, permanent pore blockade is not seen. We show application of this platform to detection of the anthrax lethal factor sequence.