General digital microfluidic platform manipulating dielectric and conductive droplets by dielectrophoresis and electrowetting
A general digital (droplet-based) microfluidic platform based on the study of dielectric droplet manipulation by dielectrophoresis (DEP) and the integration of DEP and electrowetting-on-dielectric (EWOD) is reported. Transporting, splitting, and merging dielectric droplets are achieved by DEP in a parallel-plate device, which expands the fluids of digital microfluidics from merely being conductive and aqueous to being non-conductive. In this work, decane, hexadecane, and silicone oil droplets were successfully transported in a 150 µm-high gap between two parallel plates by applying a DC voltage above threshold voltages. Non-volatile silicone oil droplets with viscosities of 20 and 50 cSt were studied in more detail in parallel-plate geometries with spacings of 75 µm, 150 µm, and 225 µm. The threshold voltages and the required driving voltages to achieve droplet velocities up to 4 mm/s in the different circumstances were measured. By adding a dielectric layer on the driving electrodes of the tested parallel-plate device, a general digital microfluidic platform capable of manipulating both dielectric and conductive droplets was demonstrated. DEP and EWOD, selectively generated by applying different signals on the same dielectric-covered electrodes, were used to drive silicone oil and water droplets, respectively. Concurrent transporting silicone oil and water droplets along an electrode loop, merging water and oil droplets, and transporting and separating the merged water-in-oil droplet were performed.