Quantifying the dielectrophoretic force on colloidal particles in microfluidic devices

We use theory, simulation, and experiment to quantify the dielectrophoretic force produced on spherical colloidal particles exposed to an interdigitated electrode array in a microfluidic environment. Our analytical predictions are based on a simplified two-dimensional model and agree with numerical solutions based on a finite difference scheme. Theoretical predictions align with experimental results without any fitting parameters over a wide range of frequencies and applied voltages. A frequency-response function for negative-dielectrophoresis instruments is derived by developing an equivalent electrical circuit model to understand the system power requirements better. Finally, we investigate the role of electrode width and array spacing on the magnitude and distance dependence of the negative dielectrophoresis force. Our analyses show that the electrode width controls the lateral position of the particles, whereas the voltage controls the vertical position. The strongest forces are achieved when the array spacing is matched to the particle size and when the electrode width is similar to 1/3 of the array spacing. These results can improve the design and optimization of negative-dielectrophoresis microfluidic instruments for applications in the separation and purification of colloidal microparticles in microelectromechanical systems.