Two-Step Acoustic Cell Separation Based on Cell Size and Acoustic Impedance─toward Isolation of Viable Circulating Tumor Cells.

Isolation and characterization of circulating tumor cells (CTCs) present a noninvasive alternative to monitor disease progression in individual patients. However, the heterogeneous lineage specificity of CTCs makes it difficult to isolate and identify possible CTCs by a liquid biopsy. Better label-free methods for the isolation of viable CTCs are needed. Our solution is a combined approach that is inherently epitope independent. Cells are separated by size-sensitive acoustophoresis using an ultrasonic standing wave field, followed by size-insensitive, acoustic barrier-medium focusing, which enables the enrichment of viable cancer cells in blood. With standard acoustophoresis in homogeneous medium, lymphocytes and monocytes were efficiently removed, while removal of granulocytes from the target MCF7 breast cancer cells was not possible due to overlapping acoustic migration velocities for viable cells. Remaining granulocytes were removed by a second separation step with an acoustic impedance barrier-medium selectively blocking the transport of MCF7 cells to generate a clean cancer cell fraction. For two series of 500 mL samples containing 5 × 10