Efficient in-droplet separation of magnetic particles for digital microfluidics

Wang, Yizhong; Zhao, Yuejun; Cho, Sung Kwon

doi:10.1088/0960-1317/17/10/029

Cited by 85 publications

(64 citation statements)

References 24 publications

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“…After the mixing operation, the beads can be easily separated out using a magnetic field gradient. 32 Thus, bioanalytical diagnostics involving immunomagnetic separation can also be performed in such a droplet.…”

Section: Introductionmentioning

confidence: 99%

Magnetic microsphere-based mixers for microdroplets

et al. 2009

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While droplet-based microfluidic systems have several advantages over traditional flow-through devices, achieving adequate mixing between reagents inside droplet-based reactors remains challenging. We describe an active mixing approach based on the magnetic stirring of self-assembled chains of magnetic microspheres within the droplet as these stirrers experience a rotating magnetic field. We measure the mixing of a water-soluble dye in the droplet in terms of a dimensional mixing parameter as the field-rpm, fluid viscosity, and microsphere loading are parametrically varied. These show that the mixing rate has a maximum value at a critical Mason number that depends upon the operating conditions.

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Section: Introductionmentioning

confidence: 99%

Magnetic microsphere-based mixers for microdroplets

et al. 2009

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“…Magnetic concentration, [11][12][13][14] with its many advantages over other mechanisms ͑e.g., electrophoretic, 15 dielectrophoretic, 16 and optoelectronic 17 ͒, is an attractive option for integration with EWOD. Unlike electric mechanisms, for instance, magnetic interactions are generally unaffected by surface charges, pH, or ionic concentration.…”

Section: B Cell Separation On Ewod Platformmentioning

confidence: 99%

Specific binding and magnetic concentration of CD8+ T-lymphocytes on electrowetting-on-dielectric platform

et al. 2010

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In the quest to create a low-power portable lab-on-a-chip system, we demonstrate the specific binding and concentration of human CD8+ T-lymphocytes on an electrowetting-on-dielectric ͑EWOD͒-based digital microfluidic platform using antibody-conjugated magnetic beads ͑MB-Abs͒. By using a small quantity of nonionic surfactant, we enable the human cell-based assays with selective magnetic binding on the EWOD device in an air environment. High binding efficiency ͑ϳ92%͒ of specific cells on MB-Abs is achieved due to the intimate contact between the cells and the magnetic beads ͑MBs͒ produced by the circulating flow within the small droplet. MBs have been used and cells manipulated in the droplets actuated by EWOD before; reported here is a cell assay of a clinical protocol on the EWOD device in air environment. The present technique can be further extended to capture other types of cells by suitable surface modification on the MBs. © 2010 American Institute of Physics. ͓doi:10.1063/1.3509457͔ I. BACKGROUND AND MOTIVATION A. EWOD as a lab-on-a-chip platformDue to its simple design, low-power consumption, and reprogrammable fluid paths, dropletbased or digital microfluidics driven by electrowetting-on-dielectric ͑EWOD͒ 1-5 is an attractive platform to develop microfluidic devices and systems for portable or point-of-care "lab-on-a-chip" applications.6 Unlike continuous flow through channels, fluids are handled in the form of individual droplets by the locally applied electric potentials. Power consumption in EWOD ͑well below 1 mW͒ is much smaller than typical continuous microfluidic systems.7 Moreover, droplet movement is directly controlled by electrical signals, and no other inputs such as thermal, pneumatic, optical, etc., are required. These features make EWOD uniquely suited for battery operation, thus addressing a critical requirement of a portable system. Moving parts such as pumps and valves, which could be failure-prone, are not required for EWOD, enhancing its simplicity and reliability. Unlike "hardwired" channels, the fluid ͑droplet͒ path in EWOD is reconfigurable purely through software, allowing the choice between multiple testing operations on the same device using the same system. Economical mass fabrication of EWOD test chips is possible, for example, using Printed Circuit Board ͑PCB͒ fabrication 8 or rapid prototyping. 9Despite the various advantages over channel-based continuous microfluidics for a lab-on-achip platform, cell-based assays on an EWOD platform have been difficult due to "biofouling" ͑biomolecular adsorption of cells and proteins͒ on the hydrophobic EWOD surface. The ability to actuate cell samples on EWOD in an air environment has been demonstrated only recently, 10 opening up the possibility of cell separation assays on EWOD, such as the one reported here.

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“…In combination with a suitable three-dimensional structuring of the surface to create barrier or gating structures, all droplet manipulation steps, like separation, transport and fusion, can be implemented, but at the cost of increasing system complexity and decreasing flexibility [41]. In other work, magnetic particle concentration and separation was demonstrated in droplets moving in a channel [42,43] or near the bottom of an oil-filled reservoir [44], by using both permanent magnet-induced forces and electrowetting-on-dielectric droplet manipulation. A different approach is the use of a matrix of coils to generate local magnetic field gradients.…”

Section: Magnetic Dropletsmentioning

confidence: 99%

Magnetic Particle Handling in Microfluidic Systems

Gijs

2010

Microfluidics Based Microsystems

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Abstract. We present techniques and methodologies for the manipulation of magnetic micro-and nanoparticles ('beads') in microfluidic systems. We first introduce the most important forces that act on magnetic particles in a microfluidic system. Starting with the magnetic force that is responsible for the primary actuation of the magnetic particles, we discuss the viscous drag force induced when the particles are moving with a speed different from the liquid in the microfluidic channel. These forces can be combined in time and space to realize the basic manipulation steps of magnetic beads in a microfluidic system: retention, separation, mixing and transport. We also discuss the use of beads as magnetic detection labels or as magnetic force mediators inside droplets.

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Efficient in-droplet separation of magnetic particles for digital microfluidics

Cited by 85 publications

References 24 publications

Magnetic microsphere-based mixers for microdroplets

Magnetic microsphere-based mixers for microdroplets

Specific binding and magnetic concentration of CD8+ T-lymphocytes on electrowetting-on-dielectric platform

Magnetic Particle Handling in Microfluidic Systems

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