Fluidization, a process in which a granular solid phase behaves like a fluid under the influence of an imposed upward fluid flow, is routinely used in many chemical and biological engineering applications. It brings, to applications involving fluid-solid exchanges, advantages such as high surface to volume ratio, constant mixing, low flow resistance, continuous operation and high heat transfer. We present here the physics of a new miniaturized, microfluidic fluidized bed, in which gravity is replaced by a magnetic field created by an external permanent magnet, and the solid-phase is composed of magnetic microbeads with diameters ranging from 1 to 5µm. These beads can be functionalized with different ligands, catalysts or enzymes, in order to use the fluidized bed as a continuous purification column or bioreactor. It allows flow-through operations at flow-rates ranging from 100 nL/min up to 5 µL/min at low driving pressures (<100mBar) with intimate liquid/solid contact and a continuous recirculation of beads for enhanced target capture efficiencies. The physics of the system presents significant differences as compared to conventional fluidized beds, which are studied here. The effect of magnetic field profile, flow chamber shape and magnetic beads dipolar interactions on flow regimes are investigated, and the different regimes of operation described. Qualitative rules to obtain optimal operation are deduced. Finally, an exemplary use as a platform for immunocapture is provided, presenting a limit of detection of 0.2 ng/mL for 200 µL volume samples.
Iago Pereiro, Sanae Tabnaoui, Marc Fermigier, Olivia du Roure, Stephanie Descroix, Jean-Louis Viovy and Laurent Malaquin
Lab Chip, 2017, Accepted Manuscript
Received 18 Jan 2017, Accepted 20 Mar 2017
First published online 22 Mar 2017