Continuous separation of nanoparticles by type via localized DC-dielectrophoresis using asymmetric nano-orifice in pressure-driven flow

Abstract

This paper presents a nano-orifice based microfluidic device using a direct current dielectrophoresis (DC-DEP) method to continuously separate different types of micro and nanoparticles of similar sizes by their different electric conductivities in pressure-driven flow. The DC-DEP force is generated by applying a low electric potential difference via a small nano-size orifice on one side wall of the channel and a micron size orifice on the opposite wall. The particles will experience the DEP forces when passing through the vicinity of the small orifice where the strongest non-uniform electric field exists. Experiments were conducted by adjusting the electric conductivity of the suspending medium so that one kind of particles will experience positive DEP force while another experiences negative DEP. In this way, the separation of 140nm polystyrene (PS) and 150nm magnetic nanoparticles and the separation of 470nm magnetic-coated PS and 490nm PS nanoparticles were demonstrated, and the separation of 5.2μm magnetic-coated PS and 7μm PS particles and the separation of 14μm sliver-coated hollow glass beads and 15μm PS particles were also conducted. In comparison with the reported DC-DEP methods which are commonly used to separate microparticles by size and the alternative current DEP (AC-DEP) techniques which can separate different types of microparticles by applying high frequency alternating current with inserted microelectrodes, this method uses a pair of asymmetrical orifices on the opposite sides of channel walls to induce strong non-uniformity of electrical field and is capable of separating different kinds of nanoparticles. Furthermore, this method involves relatively low electric potential applied locally and hence the Joule heating effect and the electrochemical reaction at the electrodes are minimized.