# A Review on Optoelectrokinetics-Based Manipulation and Fabrication of Micro/Nanomaterials
## 3 OEK-Based Manipulation of Micro/Nanomaterials
### Separation and Assembly of Micro-Scaled Particles
By contrast, the 10 \(\upmu\)m ones were pushed away from the optical ring; (**b**) as the optical rectangle size decreased, the 10 \(\upmu\)m polystyrene beads moved towards the central area of the optical rectangle and those with the other two diameters still resided within the optical ring; (**c**) when the gap formed by the long sides of the rectangle was around 10 \(\upmu\)m, the 10 \(\upmu\)m polystyrene beads were aligned; (**d**) the 10 \(\upmu\)m polystyrene beads were separated as the rectangle size further decreased; (**e**) the rectangle was decreased to a line pattern; (**f**) the 500 nm and 1 \(\upmu\)m polystyrene beads were finally located at different positions of the OEK chip (reproduced from Ref. [42]). non-conductive microparticles such as polystyrene beads [61]. As the motorized XY stage moves at an increasing velocity, the microspheres reach their maximum velocity when they cannot follow the movement of the stage. Simulation on the electric field distribution and the ODEP force attributes the strong ODEP force to the local interaction between the optically-induced electric field and the silver shells surrounding the microspheres. The microspheres were then experimentally assembled to validate their high-accuracy positioning capabilities. Figure 7 shows how the microspheres were assembled with different spaces, i.e., from 1.39 \(\upmu\)m to 20.7 \(\upmu\)m, relative to a stable bubble [60]. The assembly of the \"O,\" \"E,\" \"T\" pattern was realized, demonstrating the ability of the OEK chip to precisely and parallelly pattern metallic microspheres into arbitrary shapes. In addition, the manipulation and assembly of hybrid metal-polymer microparticles were achieved [62]. It has been further demonstrated that OEK can serve as a versatile and programmable microrobot to perform typical micromanipulations such as \"load,\" \"transport,\" and \"deliver\" [63]. Firstly, OEK was used to manipulate custom-designed microstructures. Then, the OEK based microrobot could manipulate secondary microparticles in a parallel, multistep, contact-free and programmable manner. Figure 8 is a series of images showing the dynamic process of the OEK-based microrobot across large distances. This partially enclosed microrobot could load one 15 \(\upmu\)m diameter polystyrene bead of interest with the aid of a negative ODEP force (Figure 8A-C), followed by a translational movement of 300 \(\upmu\)m/s (Figure 8D). In addition, the OEK-based microrobot delivered this bead to the target location (Figure 8E,F). Figure 8G schematically presents the three-step process, which exhibited a higher moving velocity than when OEK was used alone. This OEK-based microrobot was also validated to be suitable for isolating single cells for clonal expansion and other biomedical applications. Figure 7: Captured images of manipulated metallic microparticles with different spaces to a bubble: (**a**) 1.39 \(\upmu\)m, (**b**) 2.5 \(\upmu\)m, (**c**) 3.3 \(\upmu\)m, (**d**) 5.3 \(\upmu\)m, (**e**) 8.4 \(\upmu\)m, (**f**) 10.6 \(\upmu\)m, and (**g**) 20.7 \(\upmu\)m; parallel assembly of metallic microspheres into images of (**h**) “O,” (**i**) “E,” (**j**) “T” (reproduced from Ref. [60]).