Abstract
The ability to focus biological particles into a designated position of a microchannel is vital for various biological applications. This paper reports particle focusing under vertical and inclined magnetic fields. We analyzed the effect of the angle of rotation (θ) of the permanent magnets and the critical Reynolds number (Rec) on the particle focusing in depth. We found that a rotation angle of 10° is preferred; a particle loop has formed when Re < Rec and Rec of the inclined magnetic field is larger than that of the vertical magnetic field. We also conducted experiments with polystyrene particles (10.4 μm in diameter) to prove the calculations. Experimental results show that the focusing effectiveness improved with increasing applied magnetic field strength or decreasing inlet flow rate.
Highlights
Continuous flow focusing of microparticles/cells is an essential step for the downstream counting [1] and analyses [2] in microfluidics
We study the magnetically induced focusing of non-magnetic particles in ferrofluids under inclined magnetic fields
Gravity and Buoyancy The gravity and buoyancy of the non-magnetic particles in ferrofluids can be written as a resultant forcTe,hFen,garsavshitoywanndin bthueoyfoalnlocwy ionfg tehqeuantoionn-m: agnetic particles in ferrofluids can be written as a resultant force, Fn, as shown in the following equation: ( ) FFnn ππDD6p33p 6 ρ ρp p
Summary
Continuous flow focusing of microparticles/cells is an essential step for the downstream counting [1] and analyses [2] in microfluidics. The non-magnetic particles suspended in the magnetic solutions are subjected to negative magnetophoresis and pushed away from the magnet [12]. Since the end of an inclined magnet will form a high gradient region near the channel wall, an enhanced negative magnetophoresis will push the nonmagnetic particles toward the centerline by placing two opposite magnets on both sides of the channel. This situation is ideal for the magnetically induced flow focusing operation. We dimensioned the magnetic field and flow field and analyzed the focusing effectiveness of the particles at the exit of the channel
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