Working principle and application of magnetic separation for biomedical diagnostic at high- and low-field gradients

Abstract

Magnetic separation is a versatile technique used in sample preparation for diagnostic purpose. For such application, an external magnetic field is applied to drive the separation of target entity (e.g. bacteria, viruses, parasites and cancer cells) from a complex raw sample in order to ease the subsequent task(s) for disease diagnosis. This separation process not only can be achieved via the utilization of high magnetic field gradient, but also, in most cases, low magnetic field gradient with magnitude less than 100 T m is equally feasible. It is the aim of this review paper to summarize the usage of both high gradient magnetic separation and low gradient magnetic separation (LGMS) techniques in this area of research. It is noteworthy that effectiveness of the magnetic separation process not only determines the outcome of a diagnosis but also directly influences its accuracy as well as sensing time involved. Therefore, understanding the factors that simultaneously influence the efficiency of both magnetic separation process and target detection is necessary. Moreover, for LGMS, there are several important considerations that should be taken into account in order to ensure its successful implementation. Hence, this review paper aims to provide an overview to relate all this crucial information by linking the magnetic separation theory to biomedical diagnostic applications.

Force acting on a cluster of magnetic nanoparticles in a gradient field: A Langevin dynamics study

“…Thus, for magnetite nanoparticles with d = 10 nm, the dipolar coupling parameter at temperature T = 300 K is λ 1; for particles with 15 nm, it is λ 3-4.5. Typical gradient values used in the so-called low gradient magnetic separation are µ 0 G ∼ 10 2 T · m −1 [14]. For magnetite nanoparticles, this corresponds to g ∼ 10 −4 .…”

Equilibrium magnetization of a quasispherical cluster of single-domain particles

“…where U Z is the Zeeman energy, U ani is the magnetic anisotropy energy, U dd is the dipole-dipole interaction energy, the summation in Eqs. (2)(3)(4) is over particles in the cluster, µ 0 is the magnetic constant, r * ij = r ij /d, r ij is the vector between centers of particles i and j.…”

“…The diameter of embedded particles can range from several to several dozen nanometers, and the characteristic size of microspheres themselves most commonly ranges from tenths to several microns. One of the most popular applications of magnetic microspheres is the magnetic cell separation -a technique that allows one to magnetically label cells of a specific type and then isolate them from a heterogeneous cell mixture using a gradient field 3,4 . Also microspheres can be used as magnetically controlled carriers for targeted drug delivery 5,6 and as force and torque transducers in magnetic tweezers designed to probe mechanical properties of biomolecules 7,8 .…”

“…Multicore nanoparticles can be thought as intermediate between single-domain nanoparticles and magnetic microspheres 12 . From the viewpoint of cell separation, nanoclusters have some advantages over micrometer-sized beads: for example, they are more stable against sedimentation and have a better binding capacity due to a higher surface-area-tovolume ratio 4,13 . Multicore nanoparticles are considered to be perspective for magnetic hyperthermia treatment 14,15 and magnetic imaging 16,17 .…”

Ultraparamagnetic Cells Formed through Intracellular Oxidation and Chelation of Paramagnetic Iron

“…To determine whether an enhanced paramagnetic phenotype can enable the manipulation of UPMAG cells using magnetic fields, we first assessed their ability to be retained in magnetically actuated cell sorting (MACS) separation columns . We found that E. coli expressing UPMAG were retained in MACS columns with 40±2.8 % efficiency—much greater than either FP or BFR cells (Figure A).…”