Traveling-wave electrohydrodynamics: A versatile method for collecting nanoscaled objects from fluids

Numerous methods for the manipulation of micro- and nanoparticles have attracted wide interest in medicine and biotechnology. Especially, lab-on-chip systems (LOC) found their applications due to their fine fluid channels being of the same length scale as the objects under test. An attribute of these micrometer-sized channels is a laminar fluid flow. In conventional LOCs, these flows are often generated by external pressure-driven pumps. An alternative path to establish the fluid transport is a high-frequency electric traveling-wave. The full potential of these electrohydrodynamic traveling-waves has not yet been fully exploited. When originally employed to transport fluids through microfluidic devices - even those of physiological electric conductivity -, new applications were discovered. One example is the mixing of parallel laminar streams in a limited channel section which otherwise requires fluidic systems with special structures and geometries. A further new appli cation is the accumulation of micro- and nanometer-sized particles by establishing vortical flows. These flows arise at the boundaries of an electrode array. We used a polydimethylsiloxane (PDMS) channel system with integrated parallel linear electrodes. When an electrical field is applied, a temperature gradient results and stationary vortices occurred. Our goal is to optimize these vortices to manipulate especially nanometre-sized particles e. g. viruses. For that, it is essential to get a better understanding of the vortices. We use the traveling-wave mechanism to accumulate artificial fluorescent beads. The advantage of our system is the defined accumulation of nanometre-sized particles in the absence of any filtering material.