A digital microfluidics system for manipulating samples in liquid droplets within a gap between a first hydrophobic surface of a bottom layer and a second hydrophobic surface of at least one disposable cartridge. Disposable cartridges comprise a body and/or a rigid cover plate. The bottom layer of each disposable cartridge is a flexible film that is sealingly attached to the body or plate. The cartridge has no spacer between the first and second hydrophobic surfaces. When using these cartridges, the bottom layers configured as a working film for manipulating samples in liquid droplets thereon, is placed on an electrode array of a digital microfluidics system. The array has individual electrodes. The digital microfluidics system also comprises a central control unit for controlling the selection of the individual electrodes of the electrode array and for providing these electrodes with individual voltage pulses for manipulating liquid droplets by electrowetting.