Splitting and switching of microfluid segments in closed channels for chemical operations in the segment-on-demand technology

Abstract Basic functional units and a preparation technology have been developed for the investigation of segment operations in larger sequences of droplets. A high reproducibility of segment operations with branched microchannel structures (0.3 mm) even up to high flow rates was achieved. A switching of segments was realized by an electrical actuation without galvanic contact. The applied voltages has been in the range between 0.1 and 1.2 kV at distances between electrodes and the fluid channel of about 100 μm resulting in electrical fields in the range of about 0.2–2.4 MV/m. The switching effect cannot be explained by a poor electrowetting or a pure electrostatic effect on the fluid segments, but is caused obviously by a combination of them. A controlled switching with frequencies up to about 5 Hz was realized by a fast optical in situ measurement and a feed-back loop between the optical measurement channel and the electro actuator. After optical detection, segments can be directed individually to one of two outlet ports. The distance between segments in the both outlet channels is directly determined by the order of switching pulses. So, it is possible to realize an automated sorting of microfluid segments and to generate arbitrarily defined microfluid segment patterns. The technique will be applied for the handling of small cell ensembles and single cells for bioassays in screenings at the nanoliter level and for combinatorial screenings in chemistry.