Effect of particle-particle interaction on dielectrophoretic single particle trap in a sudden contraction flow

Dielectrophoretic (DEP) force is significant in manipulating tiny objects in micro/nano scale. To study the effect of electric interaction force on particle manipulation, a microstructure consisting of a pair of strip electrodes and a sudden contraction micro-channel was constructed. Besides DEP force and hydrodynamic force acting on single particle, the numerical model also involved electric interaction force and force moment on two particles. The analyses revealed that the particle-particle interaction force was in the same order as that of DEP force on single trapped particle. The interaction force resulted in trapping single particle failure under continuous DEP force. Thus, pulsed DEP force, turning on/off DEP force at a given time interval, was suggested. During the “off” period, the velocity difference of the two particles located at sudden contraction micro-channel enlarged the gap between them and further weakened the particle-particle interaction. By a proof-of-concept experiment, both the trapping behavior of single particle and that of two particles were in good agreement with the model. With carefully controlled parameters, the reliable function of retaining single particle was realized by pulsed DEP.