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Magnetic manipulation of beads Disclosure Number: IPCOM000234587D
Publication Date: 2014-Jan-21
Document File: 4 page(s) / 158K

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Page 01 of 4

Magnetic manipulation of beads


Magnetic colloidal particles have found their applications in many lab-on-chip systems serving as labels, sorters, transporters and mixers 1-2. Due to their shape and properties, magnetic particles are extremely versatile. Their dynamic behavior can be precisely controlled using external fields, and their surface chemistry can be altered. Magnetic particles can be accurately detected using e.g. magnetic 3 or optical techniques 4.

     In biosensing systems, it can be advantageous to laterally move magnetic particles over a surface. For example, particles may be stored at a different position than a binding surface, and may need to be transported in a controlled way toward the binding surface during the assay. This transport may include lateral transport over the surface, which will be particularly challenging when the surface contains particles that are already bound.

     It is known that in an applied magnetic field, magnetic particles form into multi-particle structures, such as chains, columns or other types of irregularly shaped clusters. Recently it was demonstrated that chains of magnetic particles near a surface, when exposed to a rotating magnetic field, can bring fluid into motion5, e.g. to move biological cells over a surface 5. The individual particle chains can translate over the surface5 due to viscous forces near a surface. The translation, however, is not very effective as particle structures easily slip over the surface, and therefore require for example 10 complete revolutions, to displace over their whole chain length.

     Here we describe actuation protocols suited for effective translation, for a wide range of surface conditions.

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Figure 1. Schematic representation of rotaphoresis


The authors have found that the induced translation can be made much more effective by actively enhancing the interaction between the surface and particles that are very close to the surface. This interaction can be enhanced, for example by binding few particles to the surface, and/or by applying attractive forces towards the surface (such as magnetic gradients or physicochemical interactions such as based on charge, van der Waals interactions, hydrogen bonding or hydrophobic/hydrophilic effects), and/or by exploiting dissipative forces such as static or kinetic friction of at least one particle with the surface or a surface-bound structure. Figure 1 sketches a system in which the particles are kept close to the surface by a field gradient.

     In case few particles are bound to the surface, the authors find from simulations (see Figure 2) that chains of particles can be displaced over a distance equal to almost half the chain length, only by i...