This paper proposes an integrated microfluidic system that can identify, count, prepare, and sort magnetic hydrogel microparticles using alternating current (AC) magnetic susceptibility measurements. The integrated microfluidic system was composed of a microplanar coil for AC magnetic susceptibility measurements and a multifunctional microfluidic chip above the coil. Through the flow-focusing method, Fe3O4/PEGDA (Fe3O4/polyethylene glycol diacrylate) magnetic hydrogel microdroplets were generated in a microchannel, then passed over a microplanar coil, and then magnetized to generate a stray field. The strength of the stray field was related to the AC magnetic susceptibility and changed the coil’s induced voltage. By detecting the voltage change, the magnetic hydrogel microparticles could be accurately identified and counted. Furthermore, magnetic hydrogel microparticles with sufficient magnetic content were passively separated from nonmagnetic or weakly magnetic particles using a gradient magnetic field. The system integrated the preparation, identification, counting, and sorting of magnetic hydrogel microparticles and also realized AC magnetic susceptibility measurements, which is difficult to accomplish using other methods. This system shows great potential for biomedical testing and drug-carrying engineering applications, as the ability to identify and count magnetic hydrogel microparticles based on their AC magnetic susceptibility enables precise determination of drug dosage in targeted delivery, while the passive separation of particles with sufficient magnetic content from nonmagnetic or weakly magnetic ones using a gradient magnetic field allows for controlled release and targeted accumulation of therapeutic carriers.
Li et al. (2026) studied this question.