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| Microtrap for single particle has the potential applications in analytical chemistry and biology. Dielectrophoretic (DEP) force is one of the effective manners to manipulate these tiny objects. In order to clarify the effect of electric interaction force on trapping behaviour, we constructed the micro-structure that consisted of one pair of strip electrodes and a sudden contraction flow. By the proof-of-concept experiment, it was found that it was hardly to trap single 5μm polystyrene particle through just adjusting the relative strength of continous nDEP force and hydrodynamic force. Among most of situations, the trapped particles were flushed out at the same time. However, with stronger pulsed nDEP generated by turning on/off DEP at a given time interval, the reliable single particle trap was created. Meanwhile, numerical model involving DEP force, hydrodynamic force and electrostatic interaction force was carried out. The result analyses revealed that, in this structure, the particle-particle interaction force was the same order as DEP force, which resulted in the failure of trapping single particle under the continuous DEP force. For pulsed nDEP force, during "off" period, electric interaction force dispeared for a short time and the velocity difference of two particles located at various positions enlarged the distance between them. When electric field was turned on again, the particle-particle interaction became very weak and some particles became easier to flush. Thus, pulsed nDEP is the better choice to increase the selectivity of trap in DEP-based microfluidic chip. |
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| Keywords:Dielectrophoresis; Microfluidics; Interaction force; Single particle trap |
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