Abstract: The present invention relates to an assay apparatus for detecting a product in a sample. The assay apparatus comprises a fluid pathway with an input of the sample and an input for a reagent with a detectable moiety which transports the sample to a detecting means via a barrier arranged to prevent a product-reagent complex passage but allow passage of unbound reagent and sample. The apparatus also includes supply means for supplying a substance adapted to breakdown the complex into a detectable moiety which can flow through the barrier to the detecting means.