A microfluidic device and method is provided for handheld diagnostics and assays. A first substance is frozen in a cryopreservation fluid in a first well of a lid. The lid includes a first surface communicating with a first port of the first well and a second surface communicating with a second port of the first well. A porous membrane is affixed to the first surface so as to overlap the first port and a non-porous membrane is affixed to the second surface so as to overlap the second port. The first substance may be dialytically freed from the cryopreservation fluid at a user desired time. Thereafter, the lid may be moved from a first position wherein the lid is spaced from a base to a second position wherein the lid is adjacent the channel in the base such that the first substance communicates with the input of the channel.