Magnetic track array for efficient bead capture in microchannels

Abstract

Magnetism-based microsystems, as those dedicated to immunoaffinity separations or (bio)chemical reactions, take benefit of the large surface area-to-volume ratio provided by the immobilized magnetic beads, thus increasing the sensitivity of the analysis. As the sensitivity is directly linked to the efficiency of the magnetic bead capture, this paper presents a simple method to enhance the capture in a microchannel. Considering a microchannel surrounded by two rectangular permanent magnets of different length (L m =2, 5, 10 mm) placed in attraction, it is shown that the amount of trapped beads is limited by the magnetic forces mainly located at the magnet edges. To overcome this limitation, a polyethylene terephthalate (PET) microchip with an integrated magnetic track array has been prototyped by laser photo-ablation. The magnetic force is therefore distributed all along the magnet length. It results in a multi-plug bead capture, observed by microscope imaging, with a magnetic force value locally enhanced. The relative amount of beads, and so the specific binding surface for further immunoassays, presents a significant increase of 300% for the largest magnets. The influence of the track geometry and relative permeability on the magnetic force was studied by numerical simulations, for the microchip operating with 2-mm-long magnets.

Efficient capture of magnetic microbeads by sequentially switched electroosmotic flow—an experimental study

“…NdFeB magnetic grains assembled onto a microfluidic chip to form alternating magnetic dipoles have been reported to efficiently remove magnetically tagged cells from suspension [19]. The use of magnetic arrays and patterned micro-magnets to distribute a strong magnetic field perpendicular to the flow has also been shown to improve the mMB capture in microfluidic channels [8,15,21,22].…”

“…To capture mMBs in microfluidic devices, researchers have developed variations in the designs of electromagneticbased separators such as magnetic micro-pillar arrays [23], electromagnetic tips [24], permalloy nanostructures [25], and micro-electromagnets with different planar geometries [14,26,27], and have also assessed the thermal dissipation from the wires or conducting coils in a microfluidic system [28]. Other studies have demonstrated the use of NdFeB magnets in their device to trap the mMBs [21,29].…”

Hybrid Magnetic-DNA Directed Immobilisation Approach for Efficient Protein Capture and Detection on Microfluidic Platforms

“…Active magnetic microsystems use on-chip micro-electromagnets that can be addressed separately 40 . Joule heating effect due to the relatively high current densities, complex processes for the integration of the micro-fabricated magnets into the microfluidic devices and the limited field strength (0–100 mT) are the drawbacks of such systems 41, 42 . On the other hand, off-chip electromagnets or permanent magnets are utilised in passive magnetic microsystems.…”

“…On the other hand, off-chip electromagnets or permanent magnets are utilised in passive magnetic microsystems. This results in a simple operation, lower cost, no unwanted heat generation, and larger magnetic fields (>0.5T) and forces 40, 42 . The fields produced by the Off-chip permanent magnets can be significantly improved by tuning the parameters including magnetic material, geometry and configuration of the magnets.…”

Magnetophoretic manipulation in microsystem using carbonyl iron-polydimethylsiloxane microstructures

“…The injection of some ferromagnetic suspension into a side channel apart from the separation channel have been reported to generate magnetic field gradients sufficient to achieve separation of magnetic beads or cells. 28 However, the flow rate enabling cell capture is relatively low: 6 ll/h. The use of micromagnets located within the channel has been reported to allow the capture of magnetic particles 29 and magnetically labeled bacterial cells 30 thus at a high technological cost.…”