Sorting of tumour cells in a microfluidic device by multi-stage surface acoustic waves

Abstract

Abstract Detection of circulating tumour cells (CTCs) plays a crucial role in the diagnosis of tumour metastasis and evaluation of therapeutic effect on prognosis. The low number of the CTCs, however, makes their isolation from the peripheral blood very difficult. In this paper, a microfluidic device has been developed, which consists of a pair of straight interdigital transducers (IDTs) and focused interdigital transducers (FIDTs), to separate tumour cells from red blood cells (RBCs) in the blood stream by surface acoustic waves (SAWs). The standing SAWs (SSAW) generated by the straight IDTs enabled placing the CTCs and RBCs at the pressure nodes while the FIDTs generated the focused travelling pulsed SAWs (TSAWs) to push the CTCs away from the blood cells to achieve the isolation of CTCs. Using this mechanism, this device was capable of concentrating and separating 2 μm and 5 μm polystyrene particles and about 94.2% of particles with the diameter of 5 μm could be collected at the outlet. Moreover, 90% ± 2.4% of U87 glioma cells could be isolated from the RBCs when the cycle number of the TSAWs was 720 k. In the enrichment process, this microfluidic device totally relied on the SSAW without any additional assistance of the flow focusing. For the separation, unlike the bidirectional acoustic radiation force in SSAW, the unidirectional force generated by TSAWs consistently pushed the particles along the wave propagation, improving the sorting performance. This multi-stage device may provide an alternative method for sorting CTCs in a reliable and flexible manner.