Magnetic Nanoparticle Aggregation and Complete De-Encapsulation of Such Aggregates from a Liquid Drop Interior

Magnetic nanoparticles (MNPs) have been extensively used for drug delivery, on-demand material deposition, etc. In this study, we demonstrate the capability to extract MNPs on-demand from a magnetic nanoparticle laden drop (MNLD) (i.e., a drop of stable aqueous dispersion of MNPs) suspended inside a highly viscous polymer (PDMS) medium in the presence of an external applied magnetic field. The phenomena involve the aggregation of MNPs inside the drop and the consequent extraction of the MNPs out of the drop with the drop retaining its original shape post-extraction. We define this latter phenomenon as de-encapsulation. This is the first study, which to the best of our knowledge, demonstrates such a removal of NPs from the interior of a drop (where the NPs, which were originally inside the drop, breach the drop interface, and get completely separated from the drop) without any permanent deformation of the drop. We further discuss how the changes in the MNP concentration and the drop volume affect the de-encapsulation distance (i.e., the distance between the drop and the location of the magnet, at the time instant when the particles leave the drop) and identify the volume of the aggregates extracted from the drop along with the mechanisms causing such de-encapsulation. We propose a theory to describe the process; our theoretical predictions capture the experimental trends well. Overall, our results in addition to demonstrating the first-of-its-kind de-encapsulation of NPs from drop interior, demonstrate a method to control the dynamics, extraction, and targeted deposition of MNPs.