Flow enhanced non-linear magnetophoretic separation of beads based on magnetic susceptibility

Abstract

Magnetic separation provides a rapid and efficient means of isolating biomaterials from complex mixtures based on their adsorption on superparamagnetic (SPM) beads. Flow enhanced non-linear magnetophoresis (FNLM) is a high-resolution mode of separation in which hydrodynamic and magnetic fields are controlled with micron resolution to isolate SPM beads with specific physical properties. In this article we demonstrate that a change in the critical frequency of FNLM can be used to identify beads with 10 magnetic susceptibilities between 0.01 and 1.0 with a sensitivity of 0.01 Hz -1 . We derived an analytical expression for the critical frequency that explicitly incorporates the magnetic and non-magnetic composition of a complex to be separated. This expression was then applied to two cases involving the detection and separation of biological targets. This study defines the operating principles of FNLM and highlights the potential for using this technique for multiplexing diagnostic assays and isolating rare cell 15 types.

Low Piconewton Towing of CNS Axons against Diffusing and Surface-Bound Repellents Requires the Inhibition of Motor Protein-Associated Pathways

“…25 individual axonal growth cones to be targeted with single beads, thereby permitting the mechanical pulling experiments to be run in parallel. The development of magnetic beads with considerably higher magnetization, compared to commercial beads, enabled significant forces to be achieved with magnetic field gradients that can be produced using commercial permanent magnets3536. Particles 1.4 µm in diameter were chosen for this study to achieve pulling forces up to 22 pN, while minimizing the torque applied during near-horizontal force application.…”

Micromagnet arrays for on-chip focusing, switching, and separation of superparamagnetic beads and single cells

“…The experimental setup was similar to those used in previous works from our group. 20,21 A magnetic field rotating in a plane parallel to the axis of motion of the beads was generated by three electromagnets arranged along mutually orthogonal axes. The solenoids were composed by 570 coils surrounding a cylindrical iron core (ASTM A536 ductile iron) 150 mm long and with diameter 60 mm.…”

“…This approach has a number of advantages over existing techniques developed for on-chip separation of magnetic beads. First, using trimagnet junctions, the beads can be separated simultaneously and continuously -a major advantage over bead separation based on differences in the critical frequency, [18][19][20][21] which would require consecutive adjustments of the field driving frequency to achieve multiplex separation. Second, tri-magnet junctions do not require a fine tuning of the driving frequencies of the applied field, as in the case for recently-demonstrated multi-frequency driven systems.…”

“…This produces multiple field maxima of the dimension of the beads, which minimises the beadbead aggregation for χ < 1. 20 The rotation of the external magnetic field creates a travelling wave of field that transports the beads across the chip at the speed of rotation. Size and magnetisationbased separation can be achieved by increasing the frequency of the travelling magnetic field to a speed where the hydrodynamic force exceeds the magnetic force.…”

“…Size and magnetisationbased separation can be achieved by increasing the frequency of the travelling magnetic field to a speed where the hydrodynamic force exceeds the magnetic force. [18][19][20][21] A critical frequency, , exists for a SPM bead…”