Continuous-flow ferrohydrodynamic sorting of particles and cells in microfluidic devices

Abstract

A new sorting scheme based on ferrofluid hydrodynamics (ferrohydrodynamics) was used to separate mixtures of particles and live cells simultaneously. Two species of cells, including Escherichia coli and Saccharomyces cerevisiae, as well as fluorescent polystyrene microparticles were studied for their sorting throughput and efficiency. Ferrofluids are stable magnetic nanoparticles suspensions. Under external magnetic fields, magnetic buoyancy forces exerted on particles and cells lead to size-dependent deflections from their laminar flow paths and result in spatial separation. We report the design, modeling, fabrication and characterization of the sorting device. This scheme is simple, low-cost and label-free compared to other existing techniques.

Continuous sheath-free magnetic separation of particles in a U-shaped microchannel

“…This technique has been demonstrated for the separations of magnetic from diamagnetic (often called nonmagnetic by non-physicists) particles, [17][18][19] magnetic from magnetic particles, [20][21][22] and diamagnetic from diamagnetic particles. [23][24][25] Its main drawback lies in the use of a sheath flow to focus particles, which not only complicates the flow control and device fabrication but also dilutes the separated particles at the cost of chemicals.…”

A novel viscoelastic-based ferrofluid for continuous sheathless microfluidic separation of nonmagnetic microparticles

“…Because ferrofluids usually have a much higher magnetic susceptibility than that of paramagnetic solutions, permanent magnets or electromagnets are sufficient to induce enough magnetophoretic force to manipulate nonmagnetic particles in microfluidics 22 . Many previous studies have reported focusing and separation of microparticles and cells using ferrofluid in microfluidics 5,16,18,[23][24][25] . In those studies, the non-magnetic particle suspension needs to be first confined by a co-flowing sheath flow; and in the downstream an external magnetic field acts on the nonmagnetic particles and deflects them into different paths 16,25 .…”

“…Many previous studies have reported focusing and separation of microparticles and cells using ferrofluid in microfluidics 5,16,18,[23][24][25] . In those studies, the non-magnetic particle suspension needs to be first confined by a co-flowing sheath flow; and in the downstream an external magnetic field acts on the nonmagnetic particles and deflects them into different paths 16,25 . It is noted that the utilization of sheath flow not only complicates the flow control and device fabrication, but also dilutes the sorted particles 24 .…”

“…The functionalized magnetic beads were used to label bioparticles because most of bioparticles in nature are non-magnetic 15 . However, the label-based methods are labour-intensive and timeconsuming, and the magnetic moments of beads may vary significantly 16 . In order to circumvent the problem, a label-free technique that uses negative magnetophoresis to manipulate and separate non-magnetic bioparticles was proposed by suspending them in a magnetic fluid, such as paramagnetic salts 17 or ferrofluid 18,19 .…”

“…In order to circumvent the problem, a label-free technique that uses negative magnetophoresis to manipulate and separate non-magnetic bioparticles was proposed by suspending them in a magnetic fluid, such as paramagnetic salts 17 or ferrofluid 18,19 . In negative magnetophoresis, effective magnetic dipole moments are induced within the microparticles, which experience a magnetic buoyancy force along the weaker field direction under non-uniform magnetic fields 16 . Paramagnetic solutions such as MnCl 2 and GdCl 3 have a poor magnetic susceptibility.…”