Cheng Wang,* Ran Zhou
Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 400 W. 13th St., MO 65409, USA
Nano-Micro Conference, 2017, 1, 01070
Published Online: 31 October 2017 (Abstract)
Citation Information: Cheng Wang, Ran Zhou, Focusing and Separating Diamagnetic Microparticles with Multiphase Ferrofluids. Nano-Micro Conference, 2017, 1, 01070 doi: 10.11605/cp.nmc2017.01070
Received: 29 May 2017, Accepted: 12 June 2017, Published Online: 31 October 2017
Ferrofluids have demonstrated great potential for a variety of manipulations of diamagnetic (or non-magnetic) micro-particles/cells in microfluidics, including sorting, focusing, and enriching. By utilizing size-dependent magnetophoresis velocity, most of the existing techniques employ single phase ferrofluids to push particles towards channel walls. In this work, we demonstrate a novel strategy for focusing and separating diamagnetic micro-particles by using the laminar fluid interface of two co-flowing fluids -- a ferrofluid and a non-magnetic fluid . As shown in Figure 1, next to the microfluidic channel, microscale magnets are fabricated to generate strong localized magnetic field gradients and forces. Due to the negative magnetophoresis force, diamagnetic particles suspended in the ferrofluid phase migrate across the ferrofluid stream at size-dependent velocities. Because of the low Reynolds number and high Peclet number associated with the flow, the fluid interface is sharp and stable. When the micro-particles migrate to the interface, they are accumulated near the interface, resulting in effective focusing and separation of particles. We investigated several factors that affect the focusing and separation efficiency, including susceptibility of the ferrofluid, distance between the microfluidic channel and microscale magnet, and width of the microfluidic channel. This concept can be extended to multiple fluid interfaces. As an example, complete separation of micro-particles was demonstrated by using a three-stream multiphase flow configuration.
Figure 1. Overview of the device and principle of particle separation. (a) a two-inlet microchannel and microscale magnets; (b) dimensions of the main fluidic channel; (c) basic principle of particle movement in a ferrofluid.
 Ran Zhou; Cheng Wang, Multiphase ferrofluid flows for micro-particle focusing and separation. Biomicrofluidics. 10, 034101 (2016). doi:10.1063/1.4948656
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