Isolating and Concentrating Rare Cancerous Cells in Large Sample Volumes of Blood by Using Dielectrophoresis and Stepping Electric Fields

Detecting rare cells, such as circulating tumor cells (CTCs), circulating fetal cells, and stem cells, is vital during medical diagnostics and characterization. During carcinogenesis, cancer cells detach from the primary tumor into the blood stream, becoming CTCs. Typical rare cell samples are considered any sample that contains less than 1000 target cells per milliliter. The volumes of microfluidic devices typically range from several microliters to nanoliters; this is excessively small for experimenting using low-concentration samples. This study involved isolating cancerous cells in an open-top chamber with sub-milliliter volumes (0.1 mL) of blood samples by using a lysis buffer solution for red blood cells (RBCs), as well as concentrating cells employing the dielectrophoretic force generated using stepping electric fields, which were produced using a handheld electric module that comprised a voltage-frequency converter and an operational amplifier. To increase the sample volume, an open-top chamber was fabricated on and bonded to a glass substrate by using circular microelectrodes. The concentrations of cancer cells and RBCs were adjusted to 500 cells/mL and 4 x 10(5) cell/ mL, respectively, for the experiments. To reduce the interference of blood cells during detection and isolate CTCs, the RBCs in the sample were lysed in a lysis buffer solution before the proposed chip was used to dielectrophoretically manipulate the rare cancerous cells. The findings indicated that the lysis buffer lysed the erythrocytes and the survivability levels of the cancerous cells (HeLa and MCF-7) remained high in the lysis buffer. The positive dielectrophoretic cancerous cells were guided based on the direction of the stepping electric field because of movement in the high-electric-field region; hence, the cancerous cells concentrated and collected at the central electrode.