Dynamics simulation of positioning and assembling multi-microparticles utilizing optoelectronic tweezers

Optoelectronic tweezer (OET) has become a powerful and versatile technique for manipulating microparticles and cells using real-time reconfigurable optical patterns. However, detailed research in the dynamics of particles in an OET device is still scarce, and the multiple-particle interactions still need further quantitative investigation. In this study, a dynamics simulation model coupling optically induced dielectrophoretic force, interaction forces between particles, and hydrodynamic and sedimentary forces is established and numerically solved by utilizing a finite element method and a dynamics simulation frame for multi-microparticles’ positioning and assembling in a typical OET device. The spatial distributions of particles in the energized OET device before optically projecting are simulated first and the condition for particle chain formation is discussed. Then, the most representative ring-shaped optical pattern is applied, and the influences of optical-ring tweezer’ dimensions of inner radius Re and width de on positioning and assembling effect are dynamically simulated and discussed for 5- and 2-μm radius particles. The simulation results indicate the particles inside and outside optical ring both undergo negative DEP and are distributed centre-symmetrically under the action of ring virtual tweezers. Average distance between the particle and center of ring (ADPC) at equilibrium and the system equilibrium time characterizing particle positioning effect dramatically increase for both 5- and 2-μm radius particles while Re increases from 35 to 55 μm. Specially, the captured particles will pile up and immediately form a three-dimensional micropyramid structure when Re approximately equals 25 μm for the 5-μm radius particle. Moreover, ADPC decreases very slowly for both two particle-sizes and the system equilibrium time of 2-μm radius particle vary more obviously than that of 5-μm radius particle with de increasing from 10 to 30 μm. And the system equilibrium time for 2-μm radius particle is always larger than that for 5-μm radius particle. The primary simulation results are in good agreement with experimental observations; hence this dynamics simulation model can truly predict the particle-moving trajectory and equilibrium positions in an OET device. Moreover, this dynamics simulation holds promise for designing and optimizing optical patterns for accuracy in assembling particles in order to form a specific microstructure.