Wetting ridge assisted programmed magnetic actuation of droplets on ferrofluid-infused surface

The actuation of droplets is necessary for several applications, including the quantitative bioanalysis of viruses. Here, authors show a programmable magnetic actuation method to manipulate droplets of various kinds by making use of the spontaneously formed ferrofluid wetting ridges around each droplet. Flexible actuation of droplets is crucial for biomedical and industrial applications. Hence, various approaches using optical, electrical, and magnetic forces have been exploited to actuate droplets. For broad applicability, an ideal approach should be programmable and be able to actuate droplets of arbitrary size and composition. Here we present an additive-free magnetic actuation method to programmably manipulate droplets of water, organic, and biological fluids of arbitrary composition, as well as solid samples, on a ferrofluid-infused porous surface. We specifically exploit the spontaneously formed ferrofluid wetting ridges to actuate droplets using spatially varying magnetic fields. We demonstrate programmed processing and analysis of biological samples in individual drops as well as the collective actuation of large ensembles of micrometer-sized droplets. Such model respiratory droplets can be accumulated for improved quantitative and sensitive bioanalysis - an otherwise prohibitively difficult task that may be useful in tracking coronavirus.

Automated summary

The study presents a programmable magnetic actuation method to manipulate droplets of various kinds using ferrofluid wetting ridges, which is crucial for biomedical and industrial applications such as processing and analyzing biological samples and collectively actuating micrometer-sized droplets.