**4. Discussion**

From the above analysis, it can be seen that the multifunctional trap and manipulation can be conducted with the fiber probe-based optical tweezers. As we know, a precise control of cell behavior was essential in the research of the endocytosis and exocytosis process, especially for nanomedicine injection, intracellular signaling pathway, and pathogenic progress. After cells manipulated in a controlled manner, various microparticles or viruses can be brought into contact with the targeted cells at specific well-defined time points and positions. Meanwhile, the spatiotemporal effect can be quantitatively investigated of different extracellular cues on the endocytosis and exocytosis process.

Then the potential application and advantages were discussed for fiber probebased tweezers on the endocytosis and exocytosis purpose. As for the nanomedicine injection, the cells can be located at a different distance to the medicine with the assistance of fiber probes, providing a great way to study the diffusion and transportation process. Further, the nanomedicine can be adjusted to approach various sites of the cell membrane. Then, the endocytosis efficiency on the interaction sites can be quantitatively investigated. Meanwhile, various nanomedicines can approach the targeted cell simultaneously with controlled sites, providing an insight into the study of selective phagocytosis progress. While for the intracellular signaling pathway, spatial manipulation will be beneficial to analyze the effect of contact distance on the cell interaction. As we know, the cell can interact with each other through the exchange of soluble signaling molecules or direct cell-cell contact, which can vary in both time and space continuously. Thus, it is of great importance in dynamically adjusting the cell-cell interaction distance and contact sequence, which can be conducted by using the fiber-probe tweezers. Further, the detailed pathway for the intracellular signaling can be individually investigated with the proposed technique. Besides, in the pathogenic progress, the specific infection site can be decided by using fiber probes to manipulate pathogenic bacterium and targeted cell simultaneously. Thus, the dependence of the contact site on the infection performance can be investigated, which opens up the possibility for analyzing pathogenic dynamics not accessible through passive observation.
