Manipulating Microvolumes of Fluids By Redox-Magnetohydrodynamics for Applications in Chemical Analysis
Authors: Nicholson Aaron G. , Rathke Nicholas , Boyd Erin , Magness Megan L. , Khan Foysal Z. , Steward Alexandria , Muldoon Timothy J. , Haggard Brian , Fritsch Ingrid 
Published: July 2021

Magnetohydrodynamics (MHD) is a unique approach for pumping fluids on a microscale and is highly suitable for enabling multiple functions for chemical analysis on a chip. An ionic current, j, is established in the fluid between selectively-activated electrodes in the presence of a magnetic field, B, that is perpendicular to the current, to generate a force, FB
, orthogonal to j and B, through the right hand rule.
FB
is a body force that propels the liquid in the same direction through momentum transfer. We use microelectrodes, which are patterned into different, individually-addressable geometries on chips. Those electrodes are modified with poly(3,4-ethylenedioxythiophene), PEDOT, a conducting polymer, that converts the applied electronic current in the external circuit to ionic current in the liquid [1] via redox (R) processes and charging. A small NdFeB permanent magnet is placed under the chip to provide B. By strategic activation of the electrodes, fluid flow can be programmed. For example, we previously demonstrated that R-MHD can start, stop, reverse, adjust speed, and alter profiles of the fluid flow. We have also shown recently that R-MHD fluid flow can be diverted in a contactless way by magnetic field gradients when paramagnetic species are present [2]. In our presentation, we will discuss recent studies on using R-MHD to control the paths of individual microvolumes of fluids for different applications, which include chemical separations of mixtures of small biologically-relevant molecules as well as fluorescence imaging [3] and identification of cyanobacteria responsible for algal blooms in fresh water samples. Fluid manipulation and flow profiles under different experimental conditions and solvent and solution compositions will be described. These involve sustained and redirection of flow, adjacent counter flows, transverse paths, sampling, and injection.

Acknowledgements:

We are grateful for financial support from the National Science Foundation (CMI-1808286) and Arkansas Bioscience Institute, the major research component of the Arkansas Tobacco Settlement Proceeds Act of 2000.

References

[1] Khan, F. Z.; Fritsch, I. “Chip-Scale Electrodeposition and Analysis of Poly(3,4-ethylenedioxythiophene) (PEDOT) Films for Enhanced and Sustained Microfluidics Using DC-Redox-Magnetohydrodynamics”, Journal of The Electrochemical Society
2019, 166 (13), H615-H627.

[2] Hähnel, V.; Khan, F. Z.; Mutschke, G.; Cierpka, C.; Uhlemann, M.; Fritsch, I. “Combining magnetic forces for contactless manipulation of fluids in microelectrode-microfluidic systems:, Scientific Reports
2019, 9:5103.

[3] Khan, F. Z.; Hutcheson, J.; Hunter, C. J.; Powless, A. J. Benson, D.; Fritsch, I.*; Muldoon, T. J.* “Redox-Magnetohydrodynamically controlled fluid flow with poly(3,4-ethylenedioxythiophene) (PEDOT) coupled to an epitaxial light sheet confocal microscope for image cytometry applications”, Anal. Chem., 2018, 90(13), 7862-7870.