Microfluidic separation of magnetic nanoparticles on an ordered array of magnetized micropillars

International audienceMicrofluidic separation of magnetic particles is based on their capture by magnetized microcollectors whilethe suspending fluid flows past the microcollectors inside a microchannel. Separation of nanoparticles is oftenchallenging because of strong Brownian motion. Low capture efficiency of nanoparticles limits their applicationsin bioanalysis. However, at some conditions, magnetic nanoparticles may undergo field-induced aggregationthat amplifies the magnetic attractive force proportionally to the aggregate volume and considerably increasesnanoparticle capture efficiency. In this paper, we have demonstrated the role of such aggregation on an efficientcapture of magnetic nanoparticles (about 80 nm in diameter) in a microfluidic channel equipped with a nickelmicropillar array. This array was magnetized by an external uniform magnetic field, of intensity as low as6–10 kA/m, and experiments were carried out at flow rates ranging between 0.3 and 30 μL/min. Nanoparticlecapture is shown to be mostly governed by the Mason number Ma, while the dipolar coupling parameter α doesnot exhibit a clear effect in the studied range, 1.4<α