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We demonstrate multifunctional silicon 3D viaduct microelectrodes for continuous-flow cell manipulation by railing and cell transfection under a modulated activation. The microelectrodes serve as tracks along which cells can rail under dielectrophoretic force and hydrodynamic drag. A modulated activation was introduced to achieve railing efficiency up to 80%. Furthermore, cell electroporation is realized through sinewave bursts applied with varying amplitude, duration and interval. Successful transfection is demonstrated by delivering 3 kDa dextran molecules into HEK293 cells with > 60% efficiency. The multifunctional 3D viaduct electrodes show great potential for continuous-flow rapid cell railing and sorting and efficient transfection.

We report on electrokinetic manipulation of submicron particles in a device with microfabricated Si electrodes featuring segmented sidewalls acting as tracks guiding particles under hydrodynamic drag. Electrohydrodynamic drag, both AC electroosmosis in low-conductive medium and electrothermal flow in high-conductive medium, gives rise to fluid rolls that deliver particles to tracks where they are held under the influence of dielectrophoretic forces. Particles are being railed along tracks under pressure-driven flow to a downstream junction where tracks act as bridges, keeping particles on course within the main channel causing their post-junction enrichment. This outcome, however, is strongly coupled to electrode sidewall contours as demonstrated here. We also report on particle oscillations under strong AC electroosmosis. Specifically, particles in deionized water can be seen bouncing off tracks or circulating with convective rolls in and out of space beneath tracks at an oscillation frequency and amplitude depending on the activation frequency. These results collectively draw attention to the functional use of electrode sidewall contours for continuous-flow manipulation of particles, which are rarely explored in microfluidics and yet could lead to more effective designs for particle separation and enrichment.

Continuous-flow electrokinetic enrichment/separation of nanoparticles is demonstrated in a device based on target nanoparticles railing along 3D microelectrode tracks. The device utilizes dielectrophoresis and electrohydrodynamic drag including electrothermal flow in high-conductive media and AC electroosmosis in low-conductive media. An enrichment efficiency of ~100% is noted for 500 nm and 1 μm polystyrene spheres in media at a conductivity of 0.2 and 0.01 S/m. Size-based separation of the two is also shown efficient in deionized water using a modified design.

We report on a unique microfluidic device that can enrich nanoparticles in a continuous flow by railing them along activated tracks (electrodes). This was achieved based on dielectrophoretic force and electrohydrodynamic drag (electrothermal rolls and AC electroosmosis) in both low and high conductive media. The results have implication for the isolation of high quality and pure nanoparticles such as exosomes from biofluids for applications in cancer diagnosis and prognosis.