Magnetophoresis

  • ■ Introduction

    Magnetophoresis is to investigate movement of magnetizable particles through a fluid under the action of a magnetic field. Here, we are developing magnetophoretic circuits for transporting and separating single magnetic particles and cells along programmable pathways in microfluidic environments, which could be considerably meaningful to unmask single-cell heterogeneity and pave a way for new medical breakthroughs. Furthermore, we are interested in microfluidic chips intergrated with planar Hall magnetoresistive (PHR) sensors for monitoring the magnetic response of directed entities and the analysis of biomolecules.

  • ■ Research output

    1) On-Chip stepping stones for magnetic carrier cruising

    We have used novel on-chip soft magnetic microstructures for magnetic carrier cruising and biomolecules translocation. Magnetic carriers can be trapped and controlled by external rotating magnetic field via novel asymmetric on-chip magnets in the microfluidic channels.  

    The potential energy landscape for a 2.8 µm diameter magnetic bead is shown as it moves around the half-disk track (10 µm diameter, 100 nm thick NiFe permalloy film). Its motion in a clockwise rotating field is presented in a–d. Blue and red colours designate the energy minima and maxima, respectively. Corresponding experimental images for the magnetic bead trajectory are shown as the dotted white line in e–h. The red arrows denote the instantaneous magnetic field direction. The multiplication factor for colour bar is 1.6x105 kBT. Scale bars, 5 µm.

    2) Magnetophoretic circuit of particle rectification

    The potential energy landscape in a clockwise rotating field in the forward-biased diode mode is shown when the external field has angular orientation as presented in a–d. The red arrows denote the instantaneous external field direction. The blue energy minima correspond to the particle locations in the experimental images of e–h. The potential energy landscape for the reverse conditions for field angles is presented in i–l along with the associated experimental images in m–p. The velocity versus frequency relationship for the matter rectifier is presented in q. The average particle velocity is determined from the time required to travel across 10 periods of the magnetic track, represented as the average (square data point) and s.d. (error bars). The theoretical fit represents an analytical solution to the nonlinear oscillator. The multiplication factor for colour bar is 1.6X105 kBT. Scale bars, 5 µm.

    3) Multiplexed circuits for arraying single particles

    The potential energy landscape in a clockwise rotating field in the forward-biased diode mode is shown when the external field has angular orientation as presented in a–d. The red arrows denote the instantaneous external field direction. The blue energy minima correspond to the particle locations in the experimental images of e–h. The potential energy landscape for the reverse conditions for field angles is presented in i–l along with the associated experimental images in m–p. The velocity versus frequency relationship for the matter rectifier is presented in q. The average particle velocity is determined from the time required to travel across 10 periods of the magnetic track, represented as the average (square data point) and s.d. (error bars). The theoretical fit represents an analytical solution to the nonlinear oscillator. The multiplication factor for colour bar is 1.6X105 kBT. Scale bars, 5 µm.

    4) Local storage of magnetically labelled single cells

    Bright-field and fluorescent images of (a) single T lymphocytes and (b) B lymphocytes trapped in individual apartments are shown. Real-time analysis of biological process, such as mitosis, can be observed in (c). A homogeneous pairing of (d) B lymphocytes and a heterogeneous pairing (e) of a B- and T lymphocytes can be trapped in a single apartment, demonstrating the ability to arrange single-cell pairs. Scale bars, 40 mm.

    1. S. Anandakumar, V. Sudha Rani, J-R. Jeong, CheolGi Kim, K. W. Kim, and B. Parvatheeswara Rao. Translocation of magnetic beads using patterned magnetic pathways for biosensing applications. J. Appl. Phys. 105, 07B312 (2009) 2. S. Anandakumar, V. Sudha Rani, Sunjong Oh, B.L. Sinha, Migaku Takahashi, CheolGi Kim. Translocation of bio-functionalized magnetic beads using smart magnetophoresis. Biosensors and Bioelectronics 26, 1755 (2010). 3. Xinghao Hu, Byunghwa Lim, Ilgyo Jeong, Adarsh Sandhu, and CheolGi Kim. Optimization of pathway pattern size for programmable biomolecule actuation. IEEE Trans. Magn. 49, 408 (2013). 4. R. Venu, B. Lim, X. H. Hu, I. Jeong, T. S. Ramulu, C. G. Kim. On-chip manipulation and trapping of microorganisms using a patterned magnetic pathway. Microfluid Nanofluid 14, 277 (2013).

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