Visualization of Magnetic Properties of Magnetic Particles in Droplet-Array Sandwiching Technology

Microfluidic droplets can be used as a field of chemical reaction to decrease reagents and reduce reaction time, and they offer great advantage for high-throughput biochemical assays. However, the transport direction is limited to downward by the effect of gravity. In this study, we observed the vertical contact-separation process of droplet arrays under an inhomogeneous magnetic field. Because the intensity of a magnetic field decays from its center to its edges, only the magnetic particles in droplets within a threshold distance from the center were transported upward. We estimated the resolution of the visualization according to the threshold distance. We then succeeded in improving the resolution of the visualization by arranging the droplet array in a partially spiral conformation. Our method could contribute to the high-throughput manipulation of magnetic materials, such as magnetically labeled cells.