Light-controlled spatiotemporal manipulation of Euglena gracilis in microfluidic channels

Precise spatiotemporal control of biological microswimmers like Euglena gracilis is crucial for advancing their use in biomedical applications such as targeted drug delivery. While E. gracilis manipulation has been demonstrated previously, quantitative characterization of their photophobic responses, particularly regarding temporal dynamics and population density, is still lacking. Here we show a novel light irradiation system integrated with a digital micromirror device (DMD) that enables precise spatiotemporal control of E. gracilis within microfluidic channels. We demonstrate trapping, collection, and bi-directional migration of E. gracilis populations using photostimulation. We quantitatively analyze microorganism density changes and migration speeds under various light stimuli conditions. Comparative analysis revealed that laser illumination achieved more than twice the boundary reflection efficiency of LED illumination due to steeper intensity gradients. The system achieves rapid response times of 30-190 s for unidirectional migration over 1 mm, significantly faster than previous reports. Furthermore, we demonstrate bi-directional migration over 2 mm while maintaining stable microswimmer density. This precise maneuvering ability of photostimulated E. gracilis has potential applications in non-invasive biomedical interventions, such as targeted drug delivery. Our work provides critical insights into the spatiotemporal control of biological microswimmers, paving the way for their integration into advanced microsystems and sensors.