We present a new approach for the manipulation of small liquid samples for the miniaturization of bioanalytical systems. In our system, minute liquid volumes are manipulated via the interaction of a changeable magnetic field and magnetic microparticles contained within aqueous droplets. Our setup enables the easy conversion of macroscopic bioanalytical protocols into the lab-on-a-chip format. Here we present the implementation of a DNA extraction and purification protocol as well as the onchip optical detection of bioactive molecules. In both cases the miniaturization results in a decrease of the reaction and detection time as well as an increase in sensitivity.