Continuous-flow Ferrohydrodynamic Sorting of Cells in Microfluidic Devices with Permanent Magnets

Microfluidicdevices for microparticle and cellular separation are becoming increasinglyimportant in miniaturized biological applications. Existing separation methods,including techniques based on channel geometry and obstacle design, opticalforce, dielectrophoresis, and magnetic bead labeling, have their ownshortcomings. Techniques based on geometries use appropriate channel andobstacle design to direct particles of different sizes into separate flowstreamlines. The dimensions of the channels and obstacles have implications forthe applicable separation size range, and a significant amount of fine-tuningis often necessary for the separation of small particles. The optical tweezertechnique employs the forces exerted by a focused laser beam to manipulatenano- to micro-scale objects. This method is usually applied to move and trap asingle object. The heating due to the focused laser beam can potentially damageliving systems. Dielectrophoresis has the potential to realize integrateddevices for high-throughput manipulation of microparticles or cells. However,its performance usually depends on the electrical properties of the specificliquid medium, particle shape, and its effective dielectric constant. Thealternating electric fields may polarize the cell membranes and lead to celldeath. The magnetic bead labeling technique, on the other hand, usesfunctionalized magnetic beads to label and separate target particles and cells.This approach takes long incubation time and is manually intensive. There isalso the difficulty of removing the magnetic labels from the target particlesor cells prior to further analysis.

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