Investigation on the focusing and separation of polystyrene microbeads in an integrated microfluidic system using magnetized functionalized flexible micro-magnet arrays

Focusing and separation of cells by microfluidic techniques are significant steps in many applications, such as single-cell analysis and disease diagnosis. Among the microfluidic techniques, passive magnetophoresis, as a label-free manner, can manipulate samples by means of magnetic field. Nowadays, most magnetic fields are generated by permanent magnets and electromagnets with large size. However, it is difficult to assemble a magnetic array using permanent magnets or electromagnets to optimize the field distribution. To produce a flexible magnetic field, a micro-magnet made by NdFeB powder and polydimethyl siloxane is proposed in this paper, and those magnetized micro-magnets are arranged into different arrays according to the arrangements of their magnetization directions. Meanwhile, a microfluidic chip containing magnetized micro-magnet arrays is designed for focusing and separating polystyrene microbeads with different diameters. The focusing and separation behaviors of microbeads in the designed microfluidic system are numerical and experimental investigated. In addition, the effects of flow rate and the arrangement of the magnetic micro-magnet array on microbead focusing and separation are discussed. Finally, a multistage microfluidic chip is designed to successfully isolate 5 μm-diameter, 10 μm-diameter, and 15 μm-diameter microbeads from their mixture at a flow rate of 240 μL/min with high purity.