Cell microarrays which sectionalized cells into microwells are powerful tool for elucidating exhaustively functions of cells at single cell level. However, there are some difficulties in taking advantages of the cell array. At first, the "single-cell occupancy", which is the ratio of microwells containing one cell to total microwell, is low. Typically, the sedimentation of cells with their own weight was used to form cell array, resulting in a low "single-cell occupancy" as low as about 50%. The second difficulty is that it takes time and effort to retrieve the target cell due to the precise and careful manipulation of the micropippet at resolution of micrometer. The broad generalization of cell microarrays requires the development of techniques to efficiently fabricate cell arrays and to easily pick up cells from cell populations. Dielectrophoresis (DEP) has become attractive because it allows for easy, rapid, and mass manipulation of cells. We have previously demonstrated the dielectrophoretic trapping cells in microwells within a few seconds with an occupation efficiency over 95% using a microwell array device. The device was fabricated by placing the upper indium-tin oxide (ITO) substrate on top of the bottom ITO electrode covered with an insulating layer with a microwell pattern. Although this device has the advantage of producing cell arrays rapidly at high density, it did not selectively manipulate the cells on the microwells. In this study, we propose a simple device for fiexible dielectrophoretic manipulation of cells based on the combination of positive DEP (p-DEP) and negative DEP (n-DEP). The use of the present device allows for accurate retrieval of the target cells from a microwell array with retaining the undesired on microwells, not to mention the forming of cell arrays. This device was comprised an upper substrate with microband electrodes mounted on a lower substrate with microwells on the same design of microband electrodes by 90 degree relative to the bottom substrate (Fig. A). The layout of electrodes enables to retrieve the target cell by the repulsive force of n-DEP induced by applying an AC voltage to two microband electrodes arranged above and below the microwell containing the target cell. Naturally, cell arrays can also be fabricated by the attractive force to bottom of microwell induced with p-DEP by applying an AC voltage to all microband electrodes.
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