Microfluidics with Alternating Current-Redox Magnetohydrodynamics at Modified Electrodes for Cell Identification

A decrease in white blood cell count below the normal range is known as leucopenia. Neutropenia is an absolute neutrophil count of less than 1500 cells per microliter of blood. This is the most common and clinically significant form of leucopenia.  In cases where patients have a count of less than 500 cells per microliter of blood, the body’s normal flora in the digestive tract can cause fatal infections and sepsis. We are developing a cost-effective method to improve monitoring of the patients’ leukocyte counts and composition. 

Leukocyte cell types (granulocytes, lymphocytes, and monocytes ) are identified via image-based classification. Microfluidics is an ideal platform for evaluation of neutrophil count, and large numbers of fluorescently-stained cells (using proflavine 0.01% w/v) may be rapidly imaged using a high-speed microscopy setup. Each cell image is quantified using image texture-based analysis. A linear discriminant analysis-based predictive classification algorithm is trained and used to group each cell into one of these three classes based solely on image texture features. This approach has been used in various other biomedical imaging applications to objectively classify cells and tissues.¹

We will report on interfacing this image-based classification method with a self-contained microfluidic pumping approach that offers parallel, uniform fluid flow, redox-magnetohydrodynamics (RMHD).  RMHD has shown the ability to move fluid in a flat flow profile across macroscopic dimensions,² so that fluid elements travel downstream at the same rate and without distortion.  This feature facilitates the counting and monitoring of the composition of cells in biological samples.

The MHD phenomenon produces a body force, F_B, whose direction and magnitude determines fluid flow, and is governed by the cross product F_B = j x B, where j is the ionic current density in solution and B is the magnetic flux density. By activating different individually-addressable microelectrodes on a chip exposed to an electrolyte and placed on a permanent magnet, and by setting the sign and magnitude of the electronic current, the ionic current density can be manipulated, and therefore the flow can be programmed.³

Early work on MHD microfluidics, reported limitations because of electrode corrosion and solvent electrolysis, resulting in bubble formation.^4,5 Subsequently, redox species were added to the solution to prevent these problems, and was coined redox-MHD (RMHD).^6,7 However the redox species can react with the sample and interfere with detection.  Replacing the solution redox species with electrode-tethered ones, such as poly(3,4-ethylenedioxythiophene) (PEDOT), a conducting polymer, resolves the complications and provides higher current and fluid speed.  Synchronizing a sinusoidal current at the modified electrode with that of the magnetic field sustains pumping at high velocities, and is called AC-RMHD.⁸  The frequencies are much lower than AC-MHD at bare electrodes where inductive heating is a problem.⁹

The performance of AC-RMHD at PEDOT-modified electrodes will be presented as it pertains to integration with image-based cell classification.  Characterization of PEDOT-modified electrodes and how biological material is affected as it flows using AC-RMHD will be described. Linear fluid flow is established between oppositely polarized, gold microband electrodes with lengths of 1.5 cm and 2.5 cm and separated by gaps as large as 5.6 mm. The solution consists of a phosphate buffer mixed with blood pipetted onto the electrode chip. The solution is contained by a rectangular cutout of a poly(dimethylsiloxane) film and sealed on top with a glass cover slip.  

Acknowledgments

Research was supported through the National Science Foundation (CBET-1336853) and the Arkansas Biosciences Institute, the major research component of the Arkansas Tobacco Settlement Proceeds Act of 2000.

References

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