Apparatus for performing an assay to detect the presence of an analyte in a test sample. A housing defines a slot for receiving a sample collector, and a capsule contains a buffer liquid, the capsule being sealed by an openable lid, and being connected to the housing such that insertion of a sample collector into the slot causes the lid to open releasing the buffer liquid into the slot. The housing further defines an incubation chamber containing or configured to receive a reagent, and an aperture permitting liquid communication between the slot and the incubation chamber. The apparatus comprises one or more test elements, a substantially liquid tight sealing member separating the incubation chamber and the test element(s), and an activation mechanism operable to open the liquid tight sealing member thereby bringing at least a portion of the or each test element into liquid communication with the incubation chamber.