Fundamental studies of circular redox-magnetohydrodynamic microfluidics and adjacent counterflows with PEDOT-modified electrodes having different geometries and sizes.

by Nicholson, Aaron G.; Fritsch, Ingrid

Understanding fluid velocity profiles of circular microfluidic flows using redox-MHDs (R-MHD) is an initial step toward lab-on-a-chip (LOAC) devices that utilize loop-based pumping concepts for chem. sepns. by liq. chromatog. The ability of R-MHD to pump in a loop within a self-contained compartment and to move small vols. in a bi-directional and programmable manner is advantageous. In addn., it has the unique capability to pump adjacent streams in opposing directions (adjacent counterflows). By immobilizing the conducting polymer known as poly-3,4-ethylenedioxythiophene (PEDOT) on electrodes to produce an ionic c.d., j, bubble formation and electrode corrosion are eliminated. In the presence of a magnetic flux, B, perpendicular to j, a body force, FB, is produced, resulting from the cross-product FB = j x B, which propels the fluid in that direction. In this work, small vols. of fluid (= 500 µL) were transported between two and three individually addressable PEDOT-coated electrodes along predetd. paths based on electrode geometries photolithog. patterned on a 25.4 x 50.8 mm silicon chip. This was demonstrated in 0.100 M NaCl using individually-addressable, microfabricated ring, disk, and band electrodes on a chip over a 0.37 T NdFeB permanent magnet. Particle tracking with polystyrene microbeads focused on a horizontal plane was used to quantify the velocity profiles as a function of applied electronic current (50, 80, 100, and 185 µA) using concentric disk-ring electrodes of increasing radii (1.3 mm to 9.1 mm). For the largest adjacent counterflows configuration, ring 4-ring 5-ring 6, the max. fluid velocity measured between ring 4-ring 5 was 25 ± 1 µm/s and between ring 5-ring 6 was 23 ± 4 µm/s in opposite directions. Other configurations were tested and will be discussed. The flow data provide important insights for further development for an on-chip sampling device, as well as loop-based sepns. with more complex electrode geometries.