Enhanced separation of magnetic and diamagnetic particles in a dilute ferrofluid

Abstract

Traditional magnetic field-induced particle separations take place in water-based diamagnetic solutions, where magnetic particles are captured while diamagnetic particles flow through without being affected by the magnetic field. We demonstrate that replacing the diamagnetic aqueous medium with a dilute ferrofluid can significantly increase the throughput of magnetic and diamagnetic particle separation. This enhancement is attributed to the simultaneous positive and negative magnetophoresis of magnetic and diamagnetic particles, respectively, in a ferrofluid. The particle transport behaviors in both ferrofluid- and water-based separations are predicted using an analytical model.

Inertial migrations of cylindrical particles in rectangular microchannels: Variations of equilibrium positions and equivalent diameters

“…Different active methods resorting to external fields for particle focusing or separation have been developed, e.g., dielectrophoresis, 1-3 acoustophoresis, 4,5 magnetophoresis, 6,7 and thermophoresis. 8,9 Recently, inertial migration has been widely used for focusing, [10][11][12][13] separation, [14][15][16][17][18] filtration, 18,19 enrichment, 16,20 or hydrodynamic stretching of particles or cells 21,22 in a microfluidic device.…”

Simultaneous diamagnetic and magnetic particle trapping in ferrofluid microflows via a single permanent magnet

“…Also neglected are the dipole-dipole interactions among the same type or different types of particles in a magnetic field. Such a treatment of particle-fluid and particle-particle interactions has been demonstrated reasonable in previous theoretical studies from the groups of Mao et al, 28,32,37,40,42 Nguyen et al, 41 and Xuan et al 30,31,33,36,39 as long as the particle and ferrofluid concentrations are both low. These conditions are fulfilled in the current work because of the use of a dilute particle suspension in a diluted ferrofluid.…”

“…[28][29][30][31][32][33][36][37][38][39][40][41]47 As such, the steady-state flow field in the T-shaped microchannel, u, is governed by the conventional continuity and Navier-Stokes equations…”

“…[25][26][27] Diamagnetic particles must be re-suspended in magnetic media like ferrofluids [28][29][30][31][32][33] and paramagnetic solutions, 34,35 so that they experience negative magnetophoresis and are repelled away from the magnetic source. [36][37][38][39][40][41][42] While magnetic particle trapping has been demonstrated with single magnets placed on one side of the particle flowing microchannel, 23-27 diamagnetic particle trapping can only take place stably with one or multiple pair(s) of magnets arranged on both sides of the channel. [43][44][45][46][47] The strong attractive or repulsive force between the pair(s) of magnets often renders it difficult to align the magnets and place them close enough to the particle flowing channel.…”

Microfluidic electrical sorting of particles based on shape in a spiral microchannel

“…[6][7][8] Traditional batch separations include centrifugation, 9 electrophoresis, 10 field-flow fractionation (FFF), 11 etc. Continuous-flow separation can be implemented by imposing an external force such as electrical, 12 optical, 13 magnetic, 14 acoustic, 15 and hydrodynamic 16 forces. Channel topology-induced internal forces have also been utilized to sort particles and cells continuously, including insulator-based dielectrophoresis, 17 deterministic lateral displacement, 18 hydrodynamic filtration, 19 hydrophoresis, 20 inertial microfluidics, 21 etc.…”