Formation of high electromagnetic gradients through a particle-based microfluidic approach

The ability to generate strong magnetic field gradients is a prerequisite for efficient magnetic-based cell/bio-particle separation or concentration. Creating these gradients is difficult under microscale fluidic devices. Conventional MEMS magnetic-based microfluidic devices involve the use of non-trivial and expensive multi-layer fabrication processes in order to produce magnetic field generators/concentrators (e.g. metal coil/ferromagnetic structures) around the microfluidic channels. A microfluidic device with simplified fabrication procedures while achieving the same functional purposes of magnetic separation/concentration of particles is highly desirable. Here, we propose a simple single-layer, single-mask fabrication technique for magnetic MEMS fluidic device construction, where nickel microparticles can be monolithographically integrated into any configurations. We constructed the microfluidic device through conventional PDMS replicate molding, with injection of nickel microparticles into a side channel 25 mu m apart from the main separation channel. The nickel microparticles are responsible for bending and concentrating the external magnetic field for gradient generation. This magnetic field gradient induced magnetic forces on the particles present in the main channel. The force generated by the presence of the nickel particles is 3.31 times greater than that without the use of a magnetic field concentrator (i.e. nickel particles). The proposed methodology can be extended for the development of automated high-throughput microfluidic cell separation devices. The simplicity of fabrication and enhanced magnetic separation efficiency shows great promise for future microfluidic systems.