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We propose a simplified multifunctional traffic control approach that effectively combines dielectrophoresis (DEP) and alternating current electrothermal (ACET) flow to realize continuous particle trapping, switching, and sorting. In the designed microsystem, the combined DEP and ACET effects, which are symmetrically generated above a bipolar electrode surface, contribute to focus the incoming colloidal particles into a thin beam. Once the bipolar electrode is energized with an electric gate signal completely in phase with the driving alternating current (AC) signal, the spatial symmetry of the electric field can be artificially reordered by adjusting the gate voltage through fieldeffect traffic control. This results in a reshapable field stagnant region for precise switching of particles into the region of interest. Moreover, the integrated particle switching prior to the scaled particle trapping experiment is successfully conducted to demonstrate the feasibility of the combined strategy. Furthermore, a mixture of two types of particle sorting (i.e., density, size) with quick response performance is achieved by increasing the driving voltage with a maximum gate voltage offset, thus, extending the versatility of the designed device. Finally, droplet switching and filtration of the satellite droplets from the parent droplets is performed to successfully permit control of the droplet traffic. The proposed traffic control approach provides a promising technique for flexible manipulation of particulate samples and can be conveniently integrated with other micro/nanofluidic components into a complete functional on-chip platform owing to its simple geometric structure, easy operation, and multifunctionality.

Multiple micromixing in a controlled sequence is an essential process for complex chemical synthesis of functional nanoparticles with desired physicochemical properties. Herein, we developed a unique sequential micromixing-assisted nanoparticle synthesis platform utilizing alternating current electrothermal flow (ACET). A two-fluid micromixer comprised with pairs of staggered asymmetric electrodes was first designed and characterized by joint numerical simulations and experiments to obtain the optimized electrode configuration within a straight channel. On this basis, an extra pair of symmetric electrodes was added at the main channel entrance to form a three-fluid sequential micromixer. The middle fluid would first mix with the side fluids through the symmetric ACET microvortex pair in the upstream region and then realize the side fluid mixing by the asymmetric ACET microvortex in the downstream region. Rapid and complete mixing in a short channel was observed for a relatively high flow velocity up to 7 mm/s at an AC signal of 27.5 V and 1 MHz. Sequential micromixing was achieved by flexibly adjusting the volume of each fluid and the AC voltage within the three-fluid mixer. Both the two-fluid mixing process and the three-fluid mixing process were applied to synthesize the Co−Fe Prussian blue analogue nanoparticles. In comparison with two-fluid mixing, three-fluid sequential mixing offers nanoparticles with higher dispersion, controlled particle morphology, and more regular shapes. Therefore, the ACET flow-based sequential micromixing strategy can be an alternative for complex chemical and biochemical reactions.

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