Abstract
Magnetophoresis-based microfluidic devices offer simple and reliable manipulation of micro-scale objects and provide a large panel of applications, from selective trapping to high-throughput sorting. However, the fabrication and integration of micro-scale magnets in microsystems involve complex and expensive processes. Here we report on an inexpensive and easy-to-handle fabrication process of micrometer-scale permanent magnets, based on the self-organization of NdFeB particles in a polymer matrix (polydimethylsiloxane, PDMS). A study of the inner structure by X-ray tomography revealed a chain-like organization of the particles leading to an array of hard magnetic microstructures with a mean diameter of 4 µm. The magnetic performance of the self-assembled micro-magnets was first estimated by COMSOL simulations. The micro-magnets were then integrated into a microfluidic device where they act as micro-traps. The magnetic forces exerted by the micro-magnets on superparamagnetic beads were measured by colloidal probe atomic force microscopy (AFM) and in operando in the microfluidic system. Forces as high as several nanonewtons were reached. Adding an external millimeter-sized magnet allowed target magnetization and the interaction range to be increased. Then, the integrated micro-magnets were used to study the magnetophoretic trapping efficiency of magnetic beads, providing efficiencies of 100% at 0.5 mL/h and 75% at 1 mL/h. Finally, the micro-magnets were implemented for cell sorting by performing white blood cell depletion.
Highlights
Microfluidic magnetophoresis has been demonstrated as an efficient way to trap and separate biological entities and is integrated in lab-on-chip systems for various biomedical applications, including clinical diagnosis [1,2]
We found that magnetic forces up to few nN are reached at contact, and the interaction distance and the magnetization of the target could be increased by adding an external millimeter-sized permanent magnet
PC-3on cancer were powder–polymer composites, led to autonomous and compact systems that were successrecovered at the output; the device could be implemented for cell sorting fully implemented for the manipulation of Superparamagnetic microbeads (SPMBs) and the sorting of magnetically labeled based on their magnetic functionalities
Summary
Biological entities—whether proteins [3,4,5], DNA [6,7,8], or cells [9,10,11]—are magnetically labeled with nano- or microparticles and are dragged towards local magnetic field maxima, generated by magnetic flux sources, with a high selectivity [12]. For a given target magnetic particle, the highest attainable force is limited to the field gradient of the magnetic field source. It is of primary interest to downsize the magnetic field source as it scales up the magnetic field gradients. With micrometer-sized magnets, local magnetic field gradients as high as 106 T/m have been reported in multipole structures [13]
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