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A magnetic-field concentrator based on microstructures has been widely used for various magnetic-based microfluidic systems to enhance the magnetic field in a microchannel.Although a nickel-integrated magnetic-field concentrator can be used for efficient magnetic manipulation,it requires complicated and expensive multi-step fabrication processes [1].To address this problem,Lin et al.proposed a nickel particle-based magnetic-field concentrator which was formed by injection of silicon oil mixed with nickel particles into the channel apart from the main channel [2].However,this method causes nonhomogeneous particle dispersion in a microchannel,resulting in decreased concentration effect.Here,we suggest a novel nickel-gelated magnetic-field concentrator for magnetic based microfluidic systems.In this study,well-distributed 5-μm nickel particles and hydrogel solution were injected into the channel,and then the nickel–hydrogel mixture was cured by ultraviolet radiation.The hydrogel limits nickel particle movements,which ensures the uniform distribution of nickel particles.For evaluation of the developed nickel-gelated magnetic field concentrator,a diamagnetophoresis system has been explored for the proof-of-concept.When the external magnetic fields applied to the system without nickel–hydrogel,there was no lateral shift and microparticles come out the same focusing position.However,as the nickel-gelated channel introduced to the system,11-μm polystyrene particle migration due to magnetic repulsion force was observed in our system.This nickel-gelated magnetic field concentrator allows the efficient magnetic manipulation without any fixed complex structures and makes significant contributions to the development of simple magnetic microfluidic system with easy integration.