Automatic magnetic manipulation of droplets on an open surface using a superhydrophobic electromagnet needle

Abstract

In this paper, we present a novel magnetic droplet manipulation platform that exploits a superhydrophobic electromagnet needle (EMN) to perform complex liquid manipulations on an open surface. By switching or adjusting the EMN power supply, the platform can simply and flexibly perform a full range of droplet manipulations, including droplet transport, fusion, mixing, magnetic beads (MBs) extraction, and droplet dispensing. Owing to its superhydrophobic coating, the EMN can directly contact a magnetic droplet and then exert a strong magnetic force on the paramagnetic beads suspended in it for effective droplet manipulation without the wetting or contamination problems. This offers particular advantages to multi-step biochemical assays. We also investigated the effects of the MBs concentrations, droplet volume, hydrophilic pattern size and current amplitude applied to the EMN on the droplet kinematics. The EMN-based droplet manipulation is facile, cost-effective, and programmable, and will significantly enhance the functionality of magnetic droplet platforms, and thus broaden their applicability to numerous fields of life science.