A cartridge manipulates samples in liquid droplets with an electrode array when a working film is placed on the array. The cartridge has a body with lower surface and wells to hold samples, each with a bottom opening to release liquid. A piercable bottom structure seals the bottom openings. A working film below the body has a hydrophobic upper surface. A peripheral spacer connects the working film to the body and forms a gap is between the body and surface. A top piercing system located in at least one of the wells has a piston and a piercing element, the piston being movable in the well and the piercing element piercing the piercable bottom structure for releasing a sample from a well into the gap.