A disposable cartridge had body, bottom layer with first hydrophobic surface, top layer with a second hydrophobic surface, and gap between. The bottom layer is a flexible film sealingly attached at its circumference to the top layer. No spacer is between the layers. The top layer has loading sites for transferring processing liquids into the gap. In use, the bottom layer is a working film for manipulating samples in liquid droplets and is placed on an electrode array of a digital microfluidics system having base unit with cartridge accommodation site and electrode array at the site. The electrode array is supported by a bottom substrate that extends in a first plane and has individual electrodes. The system also includes a central control unit for controlling selection of the electrodes and for providing these electrodes with individual voltage pulses for manipulating liquid droplets within the gap by electrowetting.