Thomas P. Forbes and Samuel P. Forry

Biochemical Science Division, Material Measurements Laboratory, NIST


Immunomagnetic isolation and magnetophoresis in microfluidics have emerged as viable techniques for the separation, fractionation, and enrichment of rare cells. Here, we present the development and characterization of a microfluidic system that incorporates a permanent magnet for the lateral magnetophoresis of paramagnetic beads and labeled cell-bead complexes. An analytical model, based on the relevant transport processes, is developed as a design tool for the demonstration and prediction of magnetophoretic displacement. We introduce a dimensionless magnetophoresis parameter to efficiently investigate the design space, gain insight into the physics of the system, and compare results across the vast spectrum of magnetophoretic microfluidic systems. The numerical model and theoretical analysis are experimentally validated by the lateral magnetophoretic deflection of paramagnetic beads and magnetically labeled breast adenocarcinoma MCF-7 cells in a microfluidic device that incorporates a permanent magnet angled relative to the flow. Through the dimensionless magnetophoresis parameter, the transition between regimes of magnetophoretic action, from hydrodynamically dominated (magnetic deflection) to magnetically dominated (magnetic capture), is experimentally identified. This powerful tool and theoretical framework enables efficient device and experiment design by identifying the necessary beads, magnet configuration (orientation), magnet type (permanent, ferromagnetic, electromagnet), flow rate, channel geometry, and buffer to achieve the desired level of magnetophoretic deflection or capture.