Manipulating fluid flow on a chip through controlled-current redox magnetohydrodynamics

by Weston, Melissa Christine; Fritsch, Ingrid

The use of controlled electronic current at microelectrodes to generate ionic current in solution allows precise and quantitative fluid manipulation on a small scale with redox-magnetohydrodynamics (redox-MHD). The MHD force, F-B(x, y, z, t), at a given time and location in solution equals the cross product of the ionic current density, j(x, y, z, t), and magnetic flux density (or magnetic induction), B(x, y, z, t), there. A quantitative relationship is experimentally established between these parameters and experimental conditions, namely the fluid velocity, v(x,y,z,t), and electronic current passing through the electrodes, i(t), providing a practical means by which to predict and control fluid flow on a small scale with great precision. The data show for our setup that the relationship between v(x, y, z, t) and i(t) is linear for a fixed B(x, y, z, t), suggesting that applying current directly to the electrodes, instead of the usual approach of applying a potential, should offer fine tuning of microfluidics and at a level and with simplicity that is not possible with other common micropumping methods. When a potential is applied, the resulting electronic current, and therefore ionic current, will fluctuate in time and from one experiment to the next because of less controllable factors: electron transfer kinetics, mass transfer (e.g. changes in convection from MHD itself), concentration (e.g. depletion of redox species) and fouling of the electrode. A comparison is made between fluid flow generated by redox-MHD using applied electronic current and applied potential. The data also show that the relationship between vertical bar v(x, y, z, t)vertical bar and vertical bar B(x, y, z, t)vertical bar is linear. In addition, effects of cell geometries on velocities were investigated. The studies involved microscope visualization to track microbeads to monitor fluid velocity in a small volume of solution containing electroactive potassium ferri- and ferrocyanide at microband arrays in the presence of permanent magnets. Also, overall flow profiles were similar for three different bead types (6-mu m sulfate, 10-mu m sulfate, and 6-mu m amino-functionalized). (C) 2012 Elsevier B.V. All rights reserved.

Journal
Sensors and Actuators B-Chemical
Volume
173
Year
2012
Start Page
935
ISBN/ISSN
0925-4005
DOI
10.1016/j.snb.2012.07.006