Sub-micron particles including nanocapsules, liposomes and exosomes are widely utilized in industries from medication to energy harvesting. Effective enrichment and separation of particles are vital in these applications. Dielectrophoretic microfluidic devices show advantages for particle manipulation, such as being label-free and highly effective, but usually operate in batch mode. They also use mostly thin-film electrodes that extend exponentially attenuated electric fields, leading to low performance.

Here, we demonstrate continuous flow electrokinetic enrichment and the separation of sub-micron particles by railing them along 3D microelectrode tracks on the sidewalls of 20 μm or 100 μm microchannels. The microelectrodes exhibit various sidewall designs including tracks, bridges and...[ Read more ]

Sub-micron particles including nanocapsules, liposomes and exosomes are widely utilized in industries from medication to energy harvesting. Effective enrichment and separation of particles are vital in these applications. Dielectrophoretic microfluidic devices show advantages for particle manipulation, such as being label-free and highly effective, but usually operate in batch mode. They also use mostly thin-film electrodes that extend exponentially attenuated electric fields, leading to low performance.

Here, we demonstrate continuous flow electrokinetic enrichment and the separation of sub-micron particles by railing them along 3D microelectrode tracks on the sidewalls of 20 μm or 100 μm microchannels. The microelectrodes exhibit various sidewall designs including tracks, bridges and undercuts, which allow them to generate a complex electric field, leading to electrothermal flow in high conductivity media and to AC electroosmosis in low conductivity media. These electrohydrodynamic drags are leveraged with dielectrophoresis in the 20 μm channel to achieve particle railing and enrichment. The 100 μm channel, in comparison, attains separation simply by opposite directions of dielectrophoresis force exerted on particles of different sizes in deionized water.

Simulations on the electric fields, flow patterns and particle trajectories confirm the devices’ capability to manipulate sub-micron particles. Enrichment of 500 nm and 1 μm polystyrene spheres at ~100% effectiveness is achieved in the 20 μm channel at a conductivity of 0.2 S/m and 0.01 S/m, respectively. Separation of the two particles is also noted in the 0.01 S/m medium at 1 kHz or 1 MHz activation. Oscillatory particle movement in deionized water is observed, which likely results from the unique sidewall profile of our 3D microelectrodes. In the 100 μm channel, separation of 500 nm, 700 nm and 1 μm polystyrene spheres is demonstrated. Additionally, enrichment of exosome is presented, which shows the devices’ potential for detection and purification of exosomes and pathogens in clinical or environmental samples.