Redox-Magnetohydrodynamics for Microfluidic Control: Remote from Active Electrodes and Their Diffusion Layers

by Scrape, P. G.; Gerner, M. D.; Weston, M. C.; Fritsch, I.

Localized, directed microfluidic flow in bulk solution, far from diffusion layers at active electrodes, was induced by redox-magnetohydrodynamics (MHD) using a magnet smaller than the distance between the electrodes to tune the flow. This "remote MHD" indicates that redox species are required only at active electrodes to sustain a faradaic current, not in the bulk where microfluidic control is desired. Thus, complete separation of redox species from sample and analyte, which can be achieved by ion-conducting barriers or electrode surface modifications, will boldly expand applications of redox-MHD in micro total analysis systems. Flow was effected in a model solution of ferricyanide/ferrocyanide and potassium chloride, between two sets of electrodes located 17.5 mm apart on a chip. A stack of two permanent magnets, 6-mm wide (one-third of the interelectrode distance), was positioned under the chip between electrodes, and a 30 mu A electronic current was applied to the electrodes. The resulting ionic current led to a MHD force causing fluid flow of <= 16.9 mu m/s above the magnet, determined by video microscopy of 10-mu m latex-polystyrene microbeads and particle image velocimetry software. Calculations indicate that MHD is the major source of the observed flow, although the magnetic field gradient may affect the flow profile.

Journal of the Electrochemical Society
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1945-7111; 0013-4651