An equivalent electrical model for numerical analyses of ODEP manipulation

Opticaldielectrophoresis(ODEP)has been explored experimentally with success in manipulating microscale objects in the last 5 years. However, not much theoretical analyses have been performed to understand its operating principles in depth and also determine its limitations as a tool to manipulate micro- and nano-scale objects. In this paper, we present our work on establishing an equivalent electrical model to analyze the important physical interactions when optically induced dielectrophoretic force is used to manipulate micron-sized polystyrene beads. Simulation results show that the ODEP manipulation of microbeads is frequency-dependent and that the electrothermal effect is negligible. Furthermore, the relationship between the frequency of the applied voltage and the maximum manipulation velocity of the microbeads obtained from simulation is consistent with our experimental measurements. In addition, simulation results also show that the minimum radius of a bead that can be manipulated exponentially decreases with respect to the size of the illuminated spot. For instance, when the illuminated spot size is 1 μm, ODEP can theoretically manipulate 100 nm beads - indicating that ODEP can be extended to manipulate nano-scale objects if the illuminated spot size can be significantly reduced.