Development of High-Throughput Cell Sorting Utilizing Femtosecond Laser Impulse – Evaluation of Switching Performance –
Z.-Y. Hong1*, T. Iino1, H. Hagihara1, T. Maeno1, K. Okano1, Y. Hosokawa1
1Graduate School of Materials Science, Nara Institute of Science and Technology, Nara, Japan
* presenting author:Zhen-Yi Hong,
Pulsed laser activated cell sorting (PLACS) in microfluidic chip has attracted much attention for its potential of high-throughput sorting to overcome limitations of conventional cell sorter. When a pulsed laser is focused in high speed fluid in a microfluidic chip, a shockwave and a cavitation bubble are generated, propagate, and act to an object in the vicinity of the laser focal point as a driving force to sort the cell. The limitation of nanosecond laser PLACS reported previously was due to huge cavitation bubbles which imposed disturbances on non-targeted samples. Therefore, we proposed a new sorting method activated by femtosecond laser (fs-laser) induced impulsive force, which is faster and more compact than that induced by nanosecond laser. In addition, a higher repetition rate fs-laser was applied to achieve a sorting with high temporal and spatial precision.
20 μm fluorescent microbeads, as phantom of cells, were loaded into the microchannel of a PDMS chip with velocity of 0.5 m/s, and focused into the center flow line of the channel. This chip was set on an upright microscope, into which a 488 nm DPSS laser and 1040 nm Ytterbium fs-laser (400 fs, 1 MHz, 8 μJ/pulse) were introduced as probing and sorting sources respectively. When fluorescence from a bead excited by the probe laser was detected, single fs-laser pulse was shot at 5 μm far from the bead and the induced force kicked the bead to the collection port. At the laser shooting moment, coordinates of all targeted beads just before and after shooting were recorded, and the data were summarized as the distribution of bead’s flow line shift in perpendicular direction of the flow.
The bead’s flow line in the perpendicular direction of the flow (X) was distributed with standard deviation of 1.4 μm just before shooting. The bead position was then shifted with the fs laser irradiation, and the average value of X and its standard deviation were 39.3 and 4.8 μm respectively. This means that the beads’ positon was shifted to X = 39.3 μm with standard deviation of 4.8 μm. The histogram after the fs-laser shooting showed no overlaps with that before shooting. This result suggests that we succeeded in the 100 % sorting on this experimental condition, and facilitated our system to realize the high-throughput sorting in the future. On the basis of these results, performance of our sorting system for biological cells will be further investigated.

Keywords: Cell sorter, Femtosecond laser, Microfluidics