Continuous-flow dielectrophoretic trapping and patterning of colloidal particles in a ratchet microchannel

Trapping and concentrating particles in a continuous flow is critical for their detection and analysis as well as removal in many fields. A variety of electrical and non-electrical forces have been demonstrated to continuously capture and enrich particles in microfluidic devices. This work presents an experimental study of the development of particle trapping in an asymmetric ratchet microchannel under dc-biased ac electric fields. The dc/ac dielectrophoretic accumulation of particles in the first pair of ratchets and the dc electrokinetic shifting of particles into the second and subsequent ratchets are studied, which are found to depend on the particle moving direction with respect to the asymmetric ratchets. The dielectrophoretically trapped particles are eventually patterned into triangular zones in all but the first pair of ratchets for both the forward and backward motions. This developing process of particle trapping can be qualitatively simulated by modifying the channel geometry in the computational domain to mimic the particle chains/clusters formed in the ratchets.