Magnetophoretic Sorting of Single Cell-Containing Microdroplets

Droplet microfluidics is a promising tool for single-cell analysis since single cell can be comparted inside a tiny volume. However, droplet encapsulation of single cells still remains a challenging issue due to the low ratio of droplets containing single cells. Here, we introduce a simple and robust single cell sorting platform based on a magnetophoretic method using monodisperse magnetic nanoparticles (MNPs) and droplet microfluidics with >94% purity. There is an approximately equal amount of MNPs in the same-sized droplet, which has the same magnetic force under the magnetic field. However, the droplets containing single cells have a reduced number of MNPs, as much as the volume of the cell inside the droplet, resulting in a low magnetic force. Based on this simple principle, this platform enables the separation of single cell-encapsulated droplets from the droplets with no cells. Additionally, this device uses only a permanent magnet without any complex additional apparatus; hence, this new platform can be integrated into a single cell analysis system considering its effectiveness and convenience.