Magnetophoretic Droplet Sorting by Incorporating magnetic Nanoparticles

Abstract

We report a novel droplet-based platform using magnetophoresis for sorting single-cell encapsulated droplets. In conventional method for encapsulating target sample in droplet, the entire volume of the aqueous phase is made into droplets in a sequential manner. This method results in high percentages of empty droplets compared to target sample encapsulating droplet. The number of target sample encapsulated in droplet follows Poisson statistics. Although the portion of single sample changes with initial sample concentration in aqueous phase, it is less than 40%. Therefore, a sorting technology of specific droplets among other droplets is highly needed to enhance the encapsulation efficiency. The conventional method for sorting specific droplets requires feedback process such as image sensor, photodetector and impedance detector. Also, complex device structure is needed and channel dimension should be changed depending on the size of the target sample. In this thesis, new approach based on magnetophoretic droplet sorting is introduced by incorporating magnetic nanoparticles into the droplets which can separate droplets depending on the number of cells inside without complex feedback process and fabrication steps. We first exploited the difference in the number of nanoparticle encapsulated droplets with or without a single cell inside. The droplets encapsulating a single cell have reducing numbers of magnetic nanoparticles as much as volume of the single cell. Since magnetic force on droplets is in proportion to the number of magnetic nanoparticles, the magnetic force on single-cell encapsulated droplets is reduced. Single-cell encapsulated droplets can be separated continuously from empty cells by difference in the lateral positions because they are subjected to different magnitude of magnetic force. We successfully demonstrated the possibility of single-cell droplet sorting method with preliminary experiments using microbeads instead of real cells. This platfor...