A method of analysing for a single stranded nucleic acid present, or potentially present, in a sample comprises a step in which the target nucleic acid (if present in the sample) displaces—and hybridises to—a reporter strand originally present in an interrogating duplex structure comprised of the reporter strand and a displaceable shorter strand. The reporter strand is tagged at or adjacent one end thereof with a reporter moiety capable of providing a detectable signal. The reporter/target duplex structure is such that the reporter strand may be selectively enzymatically digested (e.g. by means of λ-exonuclease) from its end opposite the reporter moiety to release that moiety for direct or indirect detection and regenerate single stranded target, which may then cycle through a plurality of the displacement and digestion steps to result in amplification of signal.