Contactless Dielectrophoretic Handling of Diamagnetic Levitating Water Droplets in Air

Micromagnets have been reported to successfully levitate picoliter water droplets in air. Manipulation of levitating water droplets is a contamination-free alternative to digital-microfluidic labs-on-chip where droplets are handled in channels or on a substrate. An integrated electromagnetic hybrid device combining dielectrophoretic (DEP) forces to control the position of levitating droplets along a magnetic groove, is proposed. Diamagnetic forces are analytically computed with CADES while Comsol Multiphysics™ (FEM) is used for the DEP forces. Approximations of the `point dipole model´ are compared to the Maxwell Stress Tensor method applied on the 3-D model. Based on these results, an electric sequence for polarizing planar parallel Indium Tin Oxide (ITO) electrodes is proposed in order to provide a stable and accurate control of the droplet microposition along the gap. The use of these electrodes as micro-conductors to produce variable magnetic fields for magnetophoretic droplet actuation is considered and compared to DEP actuation.