A membrane-based device for multi-step assays including one or more reagents pre-dried on the device, and one or more one fluid storage zones intended to enable the automated sequential delivery of the reagents to a test zone from addition of a fluid to the device. Addition of the fluid to the device may include a single addition of the fluid to the device. The fluid storage zones may fill with the fluid when the fluid with a sample is added to the device, and then the fluid may be released to the device at a later time. In some cases, the fluid from the sample zone is wicked into both the test zone and the fluid storage zones. Preferably, the device includes multiple layers. At least one porous membrane may be disposed between at least two of the layers. Also, associated methods are disclosed.