Incorporation of Terbium into a Microalga Leads to Magnetotactic Swimmers

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 Tb³⁺. Thus, terbium-incorporated microalgae are promising candidates for magnetically steerable biohybrid microrobots.