Electrokinetic Trapping and Patterning of Colloidal Particles in Asymmetric Ratchet Microchannels

Insulator-based dielectrophoresis offers advantages over electrode-based dielectrophoresis in many ways, and has been extensively used to manipulate particles and biological species in lab-on-a-chip devices. This work exploits insulator-based dielectrophoresis in two configurations of asymmetric ratchet microchannels to trap and concentrate microscale particles using DC-biased AC voltages. It demonstrates that the dynamics of the trapping pattern in ratchet microchannels changes in response to voltages higher than the threshold trapping voltages, and also changes with progression of the trapping experiment. Numerical modeling is used to support and validate the results, and the physical interpretations of the changing dielectrophoresis are explained using a defined dimensionless trapping number. It is revealed that the orientation of the asymmetric ratchet relative to the direction of the applied DC electric field plays a key role in determining the particle trapping patterns in the ratchets.