Light-guided microrobots

Researchers at Toyohashi University of Technology, in collaboration with the Indian Institute of Technology Madras and the National Institute of Technology, Gifu College, have developed a novel system to control the movement of Euglena gracilis using laser light and a digital projector. This method enables precise spatiotemporal manipulation of Euglena with negative phototaxis, opening possibilities for biomedical applications such as targeted drug delivery.
The team, led by Professor Moeto Nagai, combined a digital micromirror device (DMD) with a blue laser to create dynamic light patterns that trap, collect, and guide E. gracilis. The system achieved unidirectional migration exceeding 1 mm in approximately 100 seconds—significantly faster than previous methods requiring 20 minutes to one hour.
"We employed a blue laser source, which generated steeper intensity gradients at spot boundaries compared to LED illumination," explained Ryoga Ono, a Master's student and co-first author. "This characteristic is critical for microorganism control." The sharper intensity gradients increased boundary reflection efficiency by more than twofold, enabling more effective manipulation.
The study demonstrated successful trapping and collection of E. gracilis, bi-directional migration over 2 mm while maintaining stable density, and quantitative analysis of density changes under various light conditions. These findings suggest potential applications in object manipulation and drug delivery using light-controlled microrobots.
The team plans to extend this system for biological and medical applications in microfluidic devices. These microrobots can collectively manipulate micro-objects that have enhanced optical properties, similar to metamaterials, and enable signal amplification in local regions. Challenges such as parallel motion control and maintaining Euglena density are also being addressed.
"Our findings contribute to the growing field of biohybrid microsystems," said Professor Nagai. "The insights gained will aid the design of actuators and sensors that use Euglena as robotic components."

Pulasta Chakrabarty, Ryoga Ono, Takuya Kohno, Shunya Okamoto, Takayuki Shibata, Tuhin Subhra Santra, and Moeto Nagai, “Light-controlled spatiotemporal manipulation of Euglena gracilis in microfluidic channels,” Sensors & Actuators: A. Physical, 2025, Vol. 387, 116414. DOI: 10.1016/j.sna.2025.116414

This research was partly supported by The Iwatani Naoji Foundation.