Flat flow profiles achieved with microfluidics generated by redox-magnetohydrodynamics.

Horizontal flow profiles having uniform velocities (3-13% RSD) at fixed heights across 0.5, 2.0, and 5.6 mm widths, with magnitudes of ≤124 μm/s, can be sustained along a ∼25.0 mm path using redox-magnetohydrodynamics (MHD) microfluidic pumping in a small volume (14.3 mm wide × 27.0 mm long × 620 μm high) on a chip. Uniform velocity profiles are important in moving volume elements without shape distortion for assays and separations for lab-on-a-chip applications. Fluid movement resulting from the MHD force (FB = j × B) was monitored with video microscopy by tracking 10 μm, polystyrene latex beads mixed into the solution. The ionic current density, j, was generated in 0.095 M K3Fe(CN)6, 0.095 M K4Fe(CN)6, and 0.095 M KCl by applying a constant current across a 0.5, 2.0, or 5.6 mm gap between an anode-cathode pair of electrodes, consisting of one to four shorted parallel, coplanar gold microbands [each 25.0 mm × 98 μm × ∼100 nm (thickness), and separated by 102 μm] fabricated on an insulated silicon substrate. By shorting the increasing numbers of microbands together, increasing currents (118, 180, 246, and 307 μA) could be applied without electrode damage, and the impact of ionic current density gradients on velocity profiles over the anodes and cathodes could also be investigated. The magnetic field, B, was produced with a 0.36 T NdFeB permanent magnet beneath the chip. Data analysis was performed using particle image velocimetry software. A vertical flow profile was also obtained in the middle of the 5.6 mm gap.