The effect of chamber size on collection efficiency and pattern in 3D electroosmosis chip

Abstract

The advantages of using electric fields to manipulate and assemble samples are the ability to control the force exerted on particles and the simplicity of fabrication. Electroosmosis, an electrokinetic effect from the interaction between ions in the electrical double layer and the electric field, has less dependency on material property compared to dielectrophoresis. The critical parameters in electroosmosis are electrical double layer, the strength of electrical field and the flow velocity field. In an attempt to find the correlation among these parameters, a 3D electroosmosis chip is fabricated with different collection chamber size. The chamber size varying from 100 to 1000 μm was defined via photolithography and the size effect on the accumulation efficiency and collection pattern were studied by numerical simulations and experiments. The amine-modified polystyrene fluorescent particles whose average size is 1μm were used for experiments. The results show that the collection efficiency is a combined effect of the strength of the tangential electric field and the flow velocity gradient. As the chamber size decreases, the strength of the tangential field decreases and then increases, but the gradient of flow velocity intensifies. For small chamber size, the tangential electrical field induces greater flow velocity and results in more high velocity region. This explains why the smaller chamber size has better collection efficiency than the larger chamber size. For electroosmosis collection, the size of the chamber is a critical parameter for efficiency consideration.