Dielectrophoretic Manipulation for Picking up and Relocating Single Cells By a Microdisk Electrode with Microcavity
Authors: Tanaka Taishu , Mizutani Fumio , Yasukawa Tomoyuki 
Published: February 2020

The handing of single cells is important for investigating characteristics of individual cells. Dielectrophoresis (DEP) has been widely used as a manipulation tool for patterning and positioning of cells. The direction of the force depends on the relative polarizabilities of cells and suspending mediums, which induces cells to move towards or against the strong electric field region. Positive-DEP (p-DEP) is a force directed cells towards the region of electric field maxima, while negative-DEP (n-DEP) is a force to repel cells from the strong electric field. Thus, the target cells can be captured and released by DEP force. In this presentation, we demonstrate dielectrophoretic manipulation using a microdisk electrode with microcavity for picking up, positioning and relocating single target cells and also applied the present technique to the patterning with living cells by manipulating the individual cells.
The needle type of Pt microelectrode tip (20 μm diameter) with the microcavity (10 μm depth) was mounted on a xyz micromanipulater. The tip was contacted to an ITO (Indium-Tin-Oxide) substrate. The tip was placed close to the target cell on the ITO substrate. The AC voltage with frequency for p-DEP (10 MHz) was then applied to the tip to capture the cell in the microcavity with a function generator, while the ITO was connected to the ground. The voltage was immediately turned off after trapping the cell. The captured cell was transferred to the desired position by moving the tip with the xyz micromanipulater and was released from the cavity by the repulsive force of n-DEP (1.0 kHz). The arrangements of the cells were obtained by repeating a series of procedures for each cell.
The capture of the cells by p-DEP was investigated. The surface of the electrode was positioned at 50 μm right from the center of the target cell. When AC voltage (10 Vpp, 10 MHz) was applied, the cell began to direct toward the tip and moved to capture in the macrocavity at 16 s. The attractive force of p-DEP by the tip with microcavity can be applicable for trapping a single cell, since relatively high electric field was formed in the microcavity. The esterase activity in the trapped cells were investigated by staining the cells. The clear fluorescence signal observed from the trapped cell in the microcavity indicates that the cell is alive.
The cell trapped in the microcavity was released by n-DEP. Again, the target cell directed toward the microcavity by attractive p-DEP force. After the voltage was turned off, the trapped cell remained in the microcavity. The trapped cell released gradually and positioned at the point of the tip after the voltage and frequency were switched to 2.0 Vpp and 1.0 kHz, respectively. The repulsive force caused by n-DEP directed the cell in microcavity toward the outside of the microcavity. The n-DEP force is useful to arrange the cells at the desired position precisely.
The patterning with cells can be performed by the capture and release of individual cells with p- and n-DEP. We picked the target cell up in the microcavity by p-DEP. The trapped cell has been remained in the microcavity during the transfer to the desired position. After manipulation to the desired position, the trapped cell was then released from the microcavity by n-DEP, and positioned at the precise address. The procedure of capture, transfer and release of the cell was repeated for other cells, resulting in the formation of pattern with cells. No cell was released from the microcavity during the transfer to the desired position even after the attractive force of p-DEP was switched off. However the use of the microelectrode without the microcavity led to the release of cells trapped at the electrode surface even though cells were directed to the electrode by the attractive force of p-DEP. Therefore, the presence of the microcavity is advantageous to transfer the trapped cells to the desired positions.