Optoelectronic tweezers induced electroosmotic vortex for manipulating microparticles swarm

Microparticle swarms have wide applications, such as targeted delivery, biosensing, and micro-scale cleaning. Effective control of these swarms is, therefore, crucial. This study reports an approach for manipulating the microparticles swarm by utilizing optoelectronic tweezers induced dynamic electroosmotic vortex. Through combined numerical simulations and experimental investigations, we confirmed that patterned light virtual electrodes create electroosmotic vortex effect at illuminated edges, since the non-uniform electric field caused by the light pattern forms a strong tangential electric field component working on an electric double layer. Subsequently, microparticles were trapped by the vortex. The results indicated that microparticles self-assemble into chain-like structures in vortex, executing stable orbital motion controlled by light pattern geometry. The orbital range reached 279.2 μm. Finally, we demonstrated that, after captured by the light-induced electroosmotic vortex, microparticle swarms can be effectively transported across a microfluidic chip. The light pattern transporting speed can reach to 154.6 μm/s. Moreover, applying different light patterns can achieve different manipulating effects. This approach offers a versatile, non-contact method for potential applications in microparticle manipulation and microscale assembly.