Abstract: An assay device configured to separate a suspension into a filtrate and a residue for testing at least one of the filtrate and the residue. The device comprises a filter aperture for a filter membrane for receiving the suspension and separating the suspension into the filtrate and the residue. The device further comprises a filtrate receiving portion; a residue receiving portion; a first buffer container; a liquid release member configured to create an outlet of the first buffer container; a filter arm comprising the filter aperture; and a user actuated switch comprising a transition structure configured to guide the filter arm. During a transition from a first set position to a second set position of the user actuated switch, the filter arm is moved such that the filter aperture is aligned with the residue receiving portion; and the liquid release member and the first buffer container are brought together.