Incorporation of Terbium into a Microalga Leads to Magnetotactic Swimmers

Abstract

Swimming microorganisms have been shown to be useful for the propulsion of microrobotic devices due to their self-powered motion. Up to now, mainly bacteria, e.g., magnetotactic bacteria (MTB), are investigated as biohybrid microrobots. But biocompatibility studies of MTB regarding medical utilizations are still lacking. Moreover, MTB require special culture conditions for their stability, which also might limit their usage for biomedical applications. Herein, a cytocompatible, highly motile microswimmer is presented from a microalga, Chlamydomonas reinhardtii, which has the capacity to carry large loads. C. reinhardtii cells are magnetized by incorporating terbium. The following analyses reveal an induced magnetic moment of a magnetized C. reinhardtii cell of 1.6 × 10 −11 emu, comparable to its counterparts used as magnetotactic microrobots. The magnetized algae are able to align to the field lines of an applied uniform magnetic field, guiding them to swim in a directional motion. In addition, C. reinhardtii cells and human cells show mutual biocompatibility, indicating that the algae cells are noncytotoxic. Furthermore, the magnetized microalgae reported here are easy to track in the human body by luminescence imaging tools due to their innate autofluorescence performance and photoluminescence of the incorporated Tb 3+ . Thus, terbium-incorporated microalgae are promising candidates for magnetically steerable biohybrid microrobots.

Microswimmer Propulsion by Two Steadily Rotating Helical Flagella

“…Of particular interest are magnetotactic bacteria, which can readily be steered by applying magnetic fields [7,8]. Organisms that are not naturally magnetotactic can also be controlled with magnetic fields after incorporation of magnetic particles; this has recently been demonstrated with the alga Chlamydomonas reinhardtii [9]. Commonly studied magnetotactic bacteria include the strains MO-1 and MC-1 ( Magnetococcus marinus ), which are similar in morphology and differ from the species most widely studied in other contexts, such as Escherichia coli , Bacillus subtilis , or Vibrio alginolyticus .…”

In Vivo Shaping of Inorganic Functional Devices using Microalgae

“…Different lanthanides accumulate in different parts of the cells 32. We also showed that the microalgae species Chlamydomonas reinhardtii , which does not produce coccoliths, takes up Tb 3+ and accumulates them as nanoparticles inside the cells 33. The accumulation of lanthanides in coccoliths were not investigated so far.…”

Magnetic Actuation Methods in Bio/Soft Robotics

“…An approach to provide magnetic properties to the microalga species C. reinhardtii is to culture them in a media containing terbium ions (Tb 3 + ). [ 237 ] These ions are known to possess magnetic properties and to present photoluminescence and could therefore potentially be used as a biomarker. The grown microalgae presented superparamagnetic properties and their motion could be controlled by magnetic fields and tracked by their photoluminescence.…”