A Customizable DNA and Microsphere-Based, Magnetically Actuated Microswimmer

Locomoting microscale robots—microswimmers—have the potential to impact numerous applications due to their ability to selectively interact with their environment with microscale control. Previous microswimmer designs lack either submicron-level precision over their construction or instantaneous control over their shape. Thus, existing microswimmer designs limit the control afforded over microswimmer interactions with their environment. This work presents a magnetically actuated microswimmer constructed from DNA and microspheres in a hybrid top-down and bottom-up assembly technique that allows for submicron-level precision over microswimmer body construction. Microscale features were fabricated via two-photon polymerization, from which polydimethylsiloxane templates were molded. Templated assembly by selective removal was used to deposit microspheres of select size and composition into the templates. This technique was confirmed to be size-selective within a population of microspheres. To construct the microswimmer, a ferromagnetic microsphere and a nonmagnetic microsphere were deposited into a template, connected with DNA nanotubes in their arrangement, magnetized, and pulled from the template. We demonstrate instantaneous control over shape changes via expansion and contraction of a microswimmer’s body in an external magnetic field. In a rotating magnetic field of constant magnitude, the microswimmer expanded as the two microspheres separated a distance of 4.1± 0.5 micrometers, approximately the distance between microspheres deposited in the template. In an oscillating magnetic field, the same microswimmer contracted and locomoted 58.8± 0.7 micrometers over 126 seconds. [2020-0183]