**2. Fiber probe-based optical tweezers**

First, we will give a detailed introduction about the fiber probe-based optical tweezers. As for optical tweezers, a focused laser beam was essential for the stable trapping and dynamic manipulation of cells. To realize a focused laser beam, the fiber probe was designed into a tapered tip, for which the laser beam will be focused by the paraboloid end. After one cell approached the beam focus, it will suffer from the optical gradient force and then attracted into the optical axis. After that, it will be pushed away from the probe tip or attracted into the focus, which depends on the struggling of optical scattering force and gradient force along the optical axis direction. After the cell was trapped one by one, a specific organization of cell pattern can be achieved with the fiber probe. Further, the organized cell pattern can be shifted dynamically in the three dimensional direction. The FPs were fabricated by drawing commercial single-mode optical fibers with a flame-heating technique. By adjusting the stretch parameters, various parabolic ends can be achieved to conduct the multifunctional manipulation of the cell. With the high flexibility, ease fabrication, and compact size, fiber probe-based optical tweezers have been widely used for the trap of dielectric microparticles and cells [28], the shift of fluorescent particles [34], and organelles in the cell [35]. Besides, it is free from the limitation on the depth of cell manipulation in the suspensions and does not require any elaborated substrates, providing a flexible platform that can be easily integrated with microfluidics.

In this chapter, we will discuss the multifunctional manipulation of cells with the designed optical fiber probes (FPs). We will show the precise regulation and

**13**

**Figure 1.**

*Optical Fiber Probe-Based Manipulation of Cells DOI: http://dx.doi.org/10.5772/intechopen.81423*

**3. Optical fiber probe-based manipulation of cells**

and extrocytosis behaviors.

**3.1 The regulation of the cell chain**

bidirectional transport of the cell chain with the FPs. Furthermore, it can also conduct the dynamic rotation and deformation of human red blood cells. With the further combination into the microfluidic technique, FPs have enabled the precise control of cell and further applied into the noninvasive analysis for the endocytosis

**Figure 1** schematically shows the formation and regulation process of an *E. coli* cell chain. After *E. coli* cells trapped one by one, a cell chain consisted of six *E. colis* was organized at the probe tip. By adjusting FP 2 to approach *E. coli* 5, the cell is rotated and orientated toward the axial direction of FP 2. Then, *E. coli* 5 is removed from the chain with the cell contact sequence changed. By shifting FP 2 along the +*x* direction, *E. coli* 5 is put between the *E. coli* 3 and 4 (**Figure 1c**). After turning off the laser in FP 2, *E. coli* 5 is gradually rotated and orientated along the axial

*Schematic of the regulation process and experimental setup. (a) A cell chain is organized at the tip of FP 1. (b) By manipulating FP 2, E. coli 5 is rotated and then removed from the cell chain. (c) E. coli 5 is added back at a new position into the chain. (d) After turning off the laser in FP 2, E. coli 5 is orientated along the axial* 

*direction of FP 1. (e) Schematic of the experiment setup [38].*

*Optical Fiber Probe-Based Manipulation of Cells DOI: http://dx.doi.org/10.5772/intechopen.81423*

*Fiber Optics - From Fundamentals to Industrial Applications*

fiber probe-based optical tweezers (FP).

**2. Fiber probe-based optical tweezers**

divided into optical scattering force and gradient force, with the direction pointed to the optical propagating direction and beam focus, respectively. The magnitude of optical force was ranged from femtonewton to nanonewton, and thus, it was the ideal chose to measure the response of biological and macromolecular system [27]. Compared to other microscopic techniques, for example, electric filed, magnetic field, and acoustic method, optical tweezers have the great potential of high precision, high flexibility, noncontact, and wide manipulation range. However, COTS faces certain challenges, such as bulky structure, limited integration, and diffraction for nanoparticles [28]. Thus, researchers have developed various schemes of optical tweezers to extend the potential application scenario, including holographic optical tweezers (HOTs), surface plasmon-based optical tweezers (SPOTs), and

For HOTs, the optical tweezer system was inserted with a diffractive beam splitter. Then the beam wavefront can be further sculptured, which can manipulate multiple cells simultaneously [29–31]. Nevertheless, appropriate algorithms are required to be elaborately designed for achieving a specific pattern of cells. In addition, the complicated optical system was consisted of dichroic mirrors, spatial light modulators, and high-numerical-aperture focusing objectives. The working distance of objectives limits the depth at which cells can be manipulated in the cell suspensions. Besides HOTs, surface plasmon-based optical tweezers (SPOTs) have also been developed to manipulate cells with high trapping stability and retaining ability, especially for the sub-microsized cells and biological molecules [32, 33]. However, once the substrates designed, the cell pattern is fixed without a flexibility to adjust and transport the cell chain dynamically. Moreover, the organization of cell pattern is also limited at a specific depth of cell suspension. Thus, there is a great need of developing a new strategy to perform the multifunctional manipula-

First, we will give a detailed introduction about the fiber probe-based optical tweezers. As for optical tweezers, a focused laser beam was essential for the stable trapping and dynamic manipulation of cells. To realize a focused laser beam, the fiber probe was designed into a tapered tip, for which the laser beam will be focused by the paraboloid end. After one cell approached the beam focus, it will suffer from the optical gradient force and then attracted into the optical axis. After that, it will be pushed away from the probe tip or attracted into the focus, which depends on the struggling of optical scattering force and gradient force along the optical axis direction. After the cell was trapped one by one, a specific organization of cell pattern can be achieved with the fiber probe. Further, the organized cell pattern can be shifted dynamically in the three dimensional direction. The FPs were fabricated by drawing commercial single-mode optical fibers with a flame-heating technique. By adjusting the stretch parameters, various parabolic ends can be achieved to conduct the multifunctional manipulation of the cell. With the high flexibility, ease fabrication, and compact size, fiber probe-based optical tweezers have been widely used for the trap of dielectric microparticles and cells [28], the shift of fluorescent particles [34], and organelles in the cell [35]. Besides, it is free from the limitation on the depth of cell manipulation in the suspensions and does not require any elaborated substrates, providing a flexible platform that can be easily integrated

In this chapter, we will discuss the multifunctional manipulation of cells with the designed optical fiber probes (FPs). We will show the precise regulation and

**12**

with microfluidics.

tion of cells.

bidirectional transport of the cell chain with the FPs. Furthermore, it can also conduct the dynamic rotation and deformation of human red blood cells. With the further combination into the microfluidic technique, FPs have enabled the precise control of cell and further applied into the noninvasive analysis for the endocytosis and extrocytosis behaviors.
