A microfluidic device is presented for the continuous separation of red blood cells (RBCs) and white blood cells (WBCs) in a label-free manner based on negative dielectrophoresis (n-DEP). An alteration of the electric field, generated by pairs of slanted electrodes (separators) that is fabricated by covering parts of single slanted electrodes with an insulating layer is used to separate cells by their sizes. The repulsive force of n-DEP formed by slanted electrodes prepared on both the top and bottom substrates led to the deflection of the cell flow in lateral directions. The presence of gaps covered with an insulating layer for the electric field on the electrodes allows the passing of RBCs through gaps, while relatively large WBCs (cultured cultured human acute monocytic leukemia cell line (THP-1 cells)) flowed along the slanted separator without passing through the gaps and arrived at an edge in the channel. The passage efficiency for RBCs through the gaps and the arrival efficiency for THP-1 cells to the upper edge in the channel were estimated and found to be 91% and 93%, respectively.
In this work, we report the control of a microparticle position within fluid flow based on its size by using a repulsive force generated with negative dielectrophoresis (n-DEP). The n-DEP based fluidic channel, which was consisted of navigator and separator electrodes, was used to manipulate the particle flow in the center of channel and to control the particle position in the fluidic flow. The mixture of 10 µm-and 20 µm-diameter particles was introduced into the channel with 30 µm height at 700 µm/s. On applying an AC voltage (23 V peak-peak and 7 MHz) to the navigator electrodes on the upper and lower substrates in a n-DEP frequency region, the suspended microparticles were guided to the center of the fluidic channel and then channelled through the passage gate positioned at the center of the channel. The AC electric field was also applied to separator electrodes, resulting in a formation of flow paths with low electric fields. The separator was consisted of the five band electrodes with the different gap spaces with the adjacent band, which allow to forming the flow paths with different electric fields. The microparticles separately flow in line along the paths formed between the band electrodes, the 10 µm-diameter particles mainly flow through the narrow path and 20 µm-diameter particles through the wide path arranged at the outside from the center. These results indicated that positions of two types of microparticles in the fluidic channel were easily separated and controlled using the n-DEP. The present procedure therefore yields a procedure for the DEP based simple and miniaturized separators.
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