Conducting-Polymer, Magnetohydrodynamic Devices for Sustained Microfluidic Pumping
Authors: Khan Foysal Z , Fritsch Ingrid 
Published: February 2020

We have developed a mechanism to indefinitely extend unidirectional pumping of fluids by redox-magnetohydrodynamics (R-MHD) in a controllable fashion for the purpose of facilitating lab-on-a-chip applications. Electrochemistry is fundamental to R-MHD microfluidics. It allows conversion of electronic current at electrodes to ionic current, j, that when in the presence of a magnetic field, B, generates the MHD force, FB,
(the magnetic component of the Lorentz force). FB
is a body force that can be generated in a localized space (without a channel, inlet, outlet, or exterior pumping mechanism) and is governed by the right-hand rule when the ionic current travels perpendicularly to the magnetic field. We use microelectrodes for pumping, which are patterned in different, individually-addressable geometries on chips, and can be selectively activated to start, stop, reverse, adjust speed, and manipulate profiles of the fluid flow. Therefore the fluid flow is programmable. By modifying the electrodes first with poly(3,4-ethylenedioxythiophene), PEDOT, a conducting polymer, we have eliminated bubble formation and electrode corrosion, while accommodating a wider variety of electrolyte solutions compatible with chemical analysis [1]. We have merged the uniform, flat flow profile generated by R-MHD between coplanar pairs of PEDOT-modified band electrodes with epitaxial light sheet confocal microscopy to perform continuous high-resolution fluorescence imaging of cellular suspensions that can count and differentiate white blood cells (i.e. granulocytes, monocytes, and lymphocytes) in a self-contained cartridge with no moving parts [2]. A disadvantage of the conducting-polymer modified R-MHD, however, is that the duration of pumping in a single direction is limited by the amount of charge contained in the polymer. We have developed a new strategy that extends the pumping time of PEDOT-modified R-MHD that involves reconfiguring the spatial and temporal relationships between j and B. Namely we have developed a simple and small device containing permanent magnets of opposite orientations in a linear array that slides beneath the microfluidics chamber in synchrony with the switching of the ionic current. This approach offers several advantages over sinusoidal AC-MHD [3], including a more constant speed with less disruption, a higher magnetic field (to produce higher fluid speeds), and dramatically simplified and less bulky instrumentation. We will report this novel approach to sustaining R-MHD pumping and its effect on the temporal evolution of the fluid flow and the impact on the flow profiles.

Acknowledgements:

We are grateful for financial support from National Science Foundation (CBET-1336853), the Women’s Giving Circle, and Arkansas Bioscience Institute, the major research component of the Arkansas Tobacco Settlement Proceeds Act of 2000.

References

[1] Nash, C. K.; Fritsch, I. Anal. Chem., 2016, 88(3), 1601-1609.
[2] Hutcheson, J. A.; Khan, F. Z.; Powless, A. J.; Benson, D.; Hunter, C.; Fritsch, I.; Muldoon, T. J. Proceedings in SPIE BiOS, 2016, 97200U-97200U.
[3] Nash, C. K. “Advanced Microfluidic Pumping at Poly(3,4-ethylenedioxythiophene)-Modified Electrodes via AC-Magnetohydrodynamics”, The 2014 Colin G. Fink Summer Research Fellowship – Summary Report, The Electrochemical Society, Interface, Winter 2014, 84.