Investigation of Particle Electrophoretic Motion in Converging-Diverging Microchannels

We studied experimentally the particle electrophoretic motion in converging-diverging microchannels on a poly(dimethylsiloxane) (PDMS) chip. The whole process of particle acceleration and deceleration was visualized through traditional optical microscopy, with which the accelerated particle electrophoretic separation is demonstrated. The effects of electric field, particle size, particle moving passage, and channel configuration on particle electrophoretic motion are examined individually. We find that the ratio of particle velocity in the throat to that in the straight channel is insensitive to both the particle moving passage and the length of converging/diverging channel, but increased for smaller particles moving through symmetric converging-diverging channels under lower electric fields. Moreover, we find that the particle velocity ratio in electrically driven flows is significantly lower than the cross-sectional area ratio of the straight channel to the throat. We have attributed this discrepancy to the particle-induced distortion in the electric potential distribution. The computed contour of electric field in a converging-diverging microchannel has revealed that the electric field is locally higher around the two poles of a particle than all other regions inside the channel.