Fiber-integrated optical tweezers for ballistic transport and trapping yeast cells

Due to their unique operational flexibility and ability to facilitate functional integration, the fascinating application of optical fibers has recently attracted significant attention in the field of optical tweezers and optical manipulation. The traditional optical fiber tweezers (OFTs) can easily trap microparticles in the front or side of the trapping tool, instead of behind. Herein, we propose and demonstrate a novel capillary optical fiber tweezer (COFT) to break the limitation of the optical trapping direction and extend the spatial range of optical trapping. The device consists of a cascade structure of single-mode fiber and capillary optical fiber (COF), which was used to excite higher-order modes in the COF. A COF taper tip was introduced to converge the multimode field, which created a focused output beam, realizing the ballistic transport of multi-yeast cells at the surface of the COF taper tip and their trapping by multiple optical potential wells of the focused output beam. The experimental results showed that the maximum transport length and speed of the cells were greater than 150 μm and 10 μm s^-1, respectively, and at least three cells could be trapped simultaneously. The simulation results showed that the trap stiffness of COFT in several potential wells was in the range of 10-40 pN μm^-1 W^-1, which indicates that COFT has a good trap performance. Therefore, COFT greatly expands the region of the optical potential well, thus guiding and trapping microparticles distributed on the entire surface of the COF taper tip. This device can also greatly improve the optical trapping ability of single or multiple microparticles, providing a new tool for researchers committed to research on micro-nano objects and cells, which is expected to be widely used in the fields of targeted drug delivery, cell dynamic analysis, microfluidic chip driving, etc.