Size scaling effects for microparticles and cells manipulated by optoelectronic tweezers

In this work, we investigated the use of optoelectronic tweezers (OET) to manipulate objects that are larger than those that are commonly positioned with standard optical tweezers. We studied the forces that could be produced on different sized polystyrene microbeads and MCF-7 breast cancer cells with light-induced dielectrophoresis (DEP). It was found that the DEP force imposed on the bead/cell did not increase linearly with the volume of the bead/cell, primarily because of the non-uniform distribution of the electric field and the field gradient above the OET bottom plate. Although this size scaling work focuses on microparticles and cells, we propose that the general physical mechanism elucidated in this research will be insightful for other micro-objects, biological samples and micro-actuators undergoing OET manipulation.