Disaggregation of microparticle clusters by induced magnetic dipole–dipole repulsion near a surface

Abstract

Ensembles of magnetic particles are known to align and aggregate into multi-particle clusters in an applied magnetic field, and the physical laws governing these processes are well described in literature. However, it has been elusive how to achieve the opposite process, i.e. the disaggregation of particle clusters in a magnetic field. We report a novel method to disaggregate clusters of superparamagnetic microparticles using time-dependent magnetic fields. The disaggregating field is designed to generate repulsive dipole-dipole forces between the particles and to stabilize the disaggregated particles on a physical surface. We demonstrate the disaggregation of large clusters of several tens of particles, within about one minute, using fields generated by a multipole electromagnet. After the disaggregation process the particles are uniformly distributed over the surface and ready for further lab-on-chip processing. Our results represent a novel methodology to disaggregate magnetic particle clusters and thereby improve the effectiveness and reproducibility of biological assays based on magnetic microparticles.

Rotating magnetic particles for lab-on-chip applications – a comprehensive review

“…Mixing of fluid can be effectuated by applying a rotating field to a chain of MPs 2,[6][7][8][9][10][11][12][13][14][15] (Fig. 1A).…”

“…15 The system can create 3D rotating magnetic fields with and without field gradient, which can for example be used to create particle chains, pull these to a substrate (Fig. 4B), and subsequently redisperse the chains to achieve distributed single particles 14 (Fig. 4C).…”

Accurate quantification of magnetic particle properties by intra-pair magnetophoresis for nanobiotechnology

“…The applied field strength was uniform in the plane of the particles, within a few percent over a 1 mm 2 surface area. 18 The magnet also creates a field gradient toward the surface, which keeps the particles at the bottom surface of the fluid chamber. Custom image processing software was used to determine the time-dependent intra-pair separations S(t) (see Figure 2).…”

Dynamics of magnetic particles near a surface: Model and experiments on field-induced disaggregation

“…With the advent of novel experimental techniques to actuate and detect magnetic particles [3,4,[8][9][10][11][12] on the level of ensembles as well as on the level of individual particles and with the advent of corresponding miniaturized microfluidic devices [3,4,10,13,14], the need appears to understand and predict the behavior of magnetic particles in variable configurations. Yet it is difficult to model and predict the dynamics of particle ensembles because the behavior of the particle ensemble is not simply an extrapolation of the behavior of single particles due to the strong magnetic interactions between the particles [15], the hydrodynamic interactions between the particles [15,16], and the interactions between the particles and microdevice surfaces [4,8,17]. To avoid tedious experimentation and trialand-error studies, it is important to develop modeling tools for in silico studies of the behavior of particles in time-varying magnetic fields and complex device geometries.…”

“…The model integrates the known basic interactions that have already been studied separately, namely, Brownian motion [18], magnetic gradient forces [19,20], magnetic dipole-dipole interactions [4,21], and particle surface interactions [4,8,18]. To evaluate the proposed numerical model, we apply it to simulate a recently reported method by which clusters of magnetic particles can be disaggregated using magnetic fields [8]. The disaggregation method is based on magnetically attracting particles to a surface while inducing repulsive magnetic dipole-dipole interactions.…”