Title : Controllable assembly and disassembly of microparticles under light-induced electric fields
Abstract:
Microscale and nanoscale particle assembly plays a critical role in material science, microfluidics, and biomedicine. However, many existing techniques suffer from limited dynamic controllability, low spatial resolution, and poor adaptability to diverse environments. In this study, we propose a reversible and controllable particle assembly method based on optically induced electric fields. By projecting structured light patterns onto a photoconductive layer, virtual electrodes are formed, generating localized electric field gradients that induce dielectrophoretic (DEP) forces. These forces enable precise manipulation of suspended microparticles—including capture, transport, assembly, and disassembly. The method was experimentally validated using both silica (SiO2) and metal-coated (Ag-SiO2) microspheres, which exhibit negative and positive DEP responses, respectively. Results show that same-type particles repel each other while opposite-type particles attract, allowing for programmable interactions under light-defined fields. Using this principle, we achieved dynamic and parallel manipulation of particles with varying sizes, enabling reversible transitions between 3D aggregates, planar assemblies, and dispersed states by tuning optical and electrical parameters. Notably, hybrid assemblies formed between SiO2 and Ag-SiO2 particles exhibited spontaneous directional motion toward the metal side, resembling self-electrophoretic behavior observed in Janus particles. Moreover, these clusters could be guided through programmable light patterns to perform controlled loading, transport, and unloading tasks. Compared to other micromanipulation and self-assembly techniques such as magnetic, acoustic, or chemical-based methods, this optically controlled strategy offers distinct advantages in spatial precision, environmental adaptability, and dynamic reconfigurability. It enables real-time, reversible assembly and disassembly without requiring embedded structures or pre-functionalized particles. These features make it a versatile and powerful tool for constructing programmable microstructures, facilitating biomedical operations, and advancing intelligent microrobotic systems.
