Abstract: An analytical device for use in determining the presence of an analyte species of interest in a liquid state includes a chromatographic membrane support along which the liquid may travel, a plurality of first detectable particles associated with a sampling region of the device at which the liquid is to be applied, the particles being capable of being moved along the support by the liquid travel and having immobilised thereon a first binding agent capable of forming a first complex with the analyte species, a threshold region provided downstream of the sampling region in the direction of liquid travel, the threshold region being provided with a second binding agent which is capable of binding to non-complexed first binding agent on the particles, and which is present in an amount, such that a detectable number of the particles only pass the threshold region if the amount of analyte species in the sample is above a predetermined level, and a detection region downstream of the threshold region in the direction o