A single inlet two-stage acoustophoresis chip enabling tumor cell enrichment from white blood cells

Metastatic disease is responsible for most cancer deaths, and hematogenous spread through circulating tumor cells (CTC) is a prerequisite for tumor dissemination. CTCs may undergo epithelial-mesenchymal transition where many epithelial cell characteristics are lost. Therefore, CTC isolation systems relying on epithelial cell markers are at risk of losing important subpopulations of cells. Here, a simple acoustophoresis-based cell separation instrument is presented. Cells are uniquely separated while maintained in their initial suspending medium, thus eliminating the need for a secondary cell-free medium to hydrodynamically pre-position them before the separation. When characterizing the system using polystyrene particles, 99.6 +/- 0.2% of 7 mu m diameter particles were collected through one outlet while 98.8 +/- 0.5% of 5 mu m particles were recovered through a second outlet. Prostate cancer cells (DU145) spiked into blood were enriched from white blood cells at a sample flow rate of 100 mu L min(-1) providing 86.5 +/- 6.7% recovery of the cancer cells with 1.1 +/- 0.2% contamination of white blood cells. By increasing the acoustic intensity a recovery of 94.8 +/- 2.8% of cancer cells was achieved with 2.2 +/- 0.6% contamination of white blood cells. The single inlet approach makes this instrument insensitive to acoustic impedance mismatch; a phenomenon reported to importantly affect accuracy in multi-laminar flow stream acoustophoresis. It also offers a possibility of concentrating the recovered cells in the chip, as opposed to systems relying on hydrodynamic pre-positioning which commonly dilute the target cells.