Research Papers

Enhanced Capture of Magnetic Microbeads Using Combination of Reduced Magnetic Field Strength and Sequentially Switched Electroosmotic Flow—A Numerical Study

[+] Author and Article Information
Debarun Das, Marwan F. Al-Rjoub

Department of Mechanical and
Materials Engineering,
University of Cincinnati,
593 Rhodes Hall, ML 0072,
Cincinnati, OH 45221

Rupak K. Banerjee

Fellow ASME
Department of Mechanical and
Materials Engineering,
University of Cincinnati,
593 Rhodes Hall, ML 0072,
Cincinnati, OH 45221
e-mail: Rupak.banerjee@uc.edu

1Corresponding author.

Manuscript received November 6, 2014; final manuscript received January 27, 2015; published online March 10, 2015. Assoc. Editor: Ram Devireddy.

J Biomech Eng 137(5), 051008 (May 01, 2015) (11 pages) Paper No: BIO-14-1553; doi: 10.1115/1.4029748 History: Received November 06, 2014; Revised January 27, 2015; Online March 10, 2015

Magnetophoretic immunoassay is a widely used technique in lab-on-chip systems for detection and isolation of target cells, pathogens, and biomolecules. In this method, target pathogens (antigens) bind to specific antibodies coated on magnetic microbeads (mMBs) which are then separated using an external magnetic field for further analysis. Better capture of mMB is important for improving the sensitivity and performance of magnetophoretic assay. The objective of this study was to develop a numerical model of magnetophoretic separation in electroosmotic flow (EOF) using magnetic field generated by a miniaturized magnet and to evaluate the capture efficiency (CE) of the mMBs. A finite-volume solver was used to compute the trajectory of mMBs under the coupled effects of EOF and external magnetic field. The effect of steady and time varying (switching) electric fields (150–450 V/cm) on the CE was studied under reduced magnetic field strength. During switching, the electric potential at the inlet and outlet of the microchannel was reversed or switched, causing reversal in flow direction. The CE was a function of the momentum of the mMB in EOF and the applied magnetic field strength. By switching the electric field, CE increased from 75% (for steady electric field) to 95% for lower electric fields (150–200 V/cm) and from 35% to 47.5% for higher electric fields (400–450 V/cm). The CE was lower at higher EOF electric fields because the momentum of the mMB overcame the external magnetic force. Switching allowed improved CE due to the reversal and decrease in EOF velocity and increase in mMB residence time under the reduced magnetic field strength. These improvements in CE, particularly at higher electric fields, made sequential switching of EOF an efficient separation technique of mMBs for use in high throughput magnetophoretic immunoassay devices. The reduced size of the magnet, along with the efficient mMB separation technique of switching can lead to the development of portable device for detection of target cells, pathogens, and biomolecules.

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Grahic Jump Location
Fig. 1

Computational domain, comprising the miniaturized magnet and the microchannel, generated using the CFD-GEOM package (CFD-GEOM, Huntsville, AL, [42])

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Fig. 2

Numerical method to compute particle (mMB) trajectory using finite-volume method

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Fig. 3

Comparison of numerically calculated EOF profile with analytical solution of Helmholtz–Smoluchowski equation (electric field applied: 275 V/cm)

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Fig. 4

Magnetic field produced by 3/8 in. cubic NdFeB magnet: comparison between experimental data (K&J Magnetics, Jamison, PA), finite volume solver (CFD-ACE+) and finite element solver (FEMM); Inset: magnetic field contour, |B|, computed by the finite volume solver.

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Fig. 5

The mMB trajectory for applied electric field of 200 V/cm demonstrating grid independent results for the computational model, shown for a section of the numerical domain

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Fig. 6

Variation of magnetic vector potential (Az) in the computational domain and magnetic force vectors in the microchannel

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Fig. 7

Trajectory of mMBs under the influence of magnetic field, for an applied electric field of 275 V/cm without switching the flow

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Fig. 8

CE for flows with and without switching

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Fig. 9

Voltage signal at the inlet and outlet reservoir to create switching in the channel for an applied voltage potential of 55 V (corresponding to electric field of 275 V/cm)

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Fig. 10

Variation of EOF profile during switching at an applied voltage of 55 V (corresponding to electric field of 275 V/cm)

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Fig. 11

CE under the effect of variable periods of switching

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Fig. 12

Comparison of CE in pressure driven flow with flows with and without switching



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