A label-free DC impedance-based microcytometer for circulating rare cancer cell counting

Quantification of circulating tumor cells (CTCs) in blood samples is believed to provide valuable evidence of cancer progression, cancer activity status, response to therapy in patients with metastatic cancer, and possible cancer diagnosis. Recently, a number of researchers reported that CTCs tend to lose their epithelial cell adhesion molecule (EpCAM) by an epithelial-mesenchymal transition (EMT). As such, label-free CTC detection methods are attracting worldwide attention. Here, we describe a label-free DC impedance-based microcytometer for CTCs by exploiting the difference in size between CTCs and blood cells. This system detects changes in DC impedance between two polyelectrolytic gel electrodes (PGEs) under low DC voltages. Using spiked ovarian cancer cell lines (OVCAR-3) in blood as a model system, we were able to count the cells using a microcytometer with 88% efficiency with a flow rate of 13 mu l min(-1) without a dilution process. Furthermore, we examined blood samples from breast cancer patients using the cytometer, and detected CTCs in 24 out of 24 patient samples. Thus, the proposed DC impedance-based microcytometer presents a facile and fast way of CTC evaluation regardless of their biomarkers.