Abstract: The present invention provides a method for detecting the presence or absence of a target analyte in a test sample, comprising the steps: i) providing a plurality of detector nanoparticles comprising a first detector nanoparticle functionalised with a first probe specific for a first region of a target analyte and a second detector nanoparticle functionalised with a second probe specific for a second region of said target analyte; and ii) contacting said detector nanoparticles with a test sample under conditions suitable for the binding of the specific probes to the target analyte, wherein target analyte-induced agglomeration of the detector nanoparticles permits the release of a detectable signal means from a signal reservoir. Also provided are related devices and systems for performing the method of the invention.