Fast manipulation of single cells in microfluidic channels utilizing femtosecond laser-induced impulsive force 2: Physical and biological behavior of Euglena gracilis
Takanori Maeno1,5*, Takeshi Yamakawa1,5, Takanori Iino1,5, Osamu Iwata2,5, Kengo Suzuki2,5, Naoki Tanaka3,5, Yudai Shibata3,5, Taisuke Nozawa3,5, Akihiro Isozaki3,5, Dino Di Carlo4,5, Keisuke Goda3,4,5, Yoichiroh Hosokawa1,5
1Graduate School of Materials Science, Nara Institute of Science and Technology, Nara, Japan
2euglena Co., Ltd, Tokyo, Japan
3Department of Chemistry, The University of Tokyo, Tokyo, Japan
4Department of Bioengineering, The University of California, Los Angels, California, Japan
5Japan Science and Technology Agency, Tokyo, Japan
* presenting author:Takanori MAENO,
Euglena, which is a kind of unicellular dinoflagellates, has attracted attention as a promising material for biomass fuel and food enriched in nutrients. For optimal production, it is important to select euglena clones that have a high capability to produce oil components or nutrition factors, and to explore an effective mass culturing method. However, it is quite difficult to select single Euglena cells with conventional cell sorting systems because of the heterogeneity in their size. To overcome this problem, we have developed a cell sorting system utilizing microfluidic channels and a femtosecond laser.
Euglena gracilis cells were introduced into a microfluidic chip including a long channel, which functions to focus the cells into the center of the channel utilizing inertial lift force. After mounting the microfluidic chip on an inverted microscope, femtosecond laser pulses (100fs, 800nm, <1.5μJ/pulse) introduced into the microscope were focused through a 20x objective lens (NA: 0.46) onto a position just upstream of a branched outlet channel. A shockwave and cavitation bubble are generated at the laser focal point, which act to generate an impulsive force on a cell in the vicinity of the laser focal point. Dynamic behavior of the cells before and after exposure to the impulsive force was monitored by a high-speed camera with frame rate of 100,000 fps. Modulated motion of the cell by the impulsive force was estimated as a shift from the focusing (alignment) position and the magnitude of the shift was evaluated as a function of flow rate, laser pulse energy, and laser focus position. Furthermore, survival rate of the cells after exposure to the impulsive force was investigated. On the basis of these experimental results, efficiency of cell sorting by the impulsive force was discussed.

Keywords: cell sorting, femtosecond laser, Euglena, microfluidic chip