Standing surface acoustic wave (SSAW)-based cell washing

Abstract

Cell/bead washing is an indispensable sample preparation procedure used in various cell studies and analytical processes. In this article, we report a standing surface acoustic wave (SSAW)-based microfluidic device for cell and bead washing in a continuous flow. In our approach, the acoustic radiation force generated in a SSAW field is utilized to actively extract cells or beads from their original medium. A unique configuration of tilted-angle standing surface acoustic wave (taSSAW) is employed in our device, enabling us to wash beads with >98% recovery rate and >97% washing efficiency. We also demonstrate the functionality of our device by preparing high-purity (>97%) white blood cells from lysed blood samples through cell washing. Our SSAW-based cell/bead washing device has the advantages of label-free manipulation, simplicity, high biocompatibility, high recovery rate, and high washing efficiency. It can be useful for many lab-on-a-chip applications.

Fig. 1

(a) A schematic of the SSAW-based cell/bead washing device for white blood cell (WBC) washing. (b) An optical image of our SSAW-based cell/bead washing device. (c) Deflection of a 9.77 μm bead from the original medium stream. Green: stacked images of a bead. Red: original medium stream indicated by red fluorescence of Rhodamine B.

Fig. 2

Demonstration of the SSAW-based bead washing. (a) When the SSAW was off, the 9.77 μm beads exited in original medium. (b) When the SSAW was on, the 9.77 μm beads got washed out and exited in wash solution. Green: stacked images of the 9.77 μm beads. Red: fluorescence images of the 0.87 μm beads indicating the original medium.

Fig. 3

(a) Influence of input voltage on recovery rate and washing efficiency for bead washing. The error bars represent the standard deviation (n=3). (b) Stacked image showing outlet region of the SSAW-based bead-washing experiment at the optimized condition.

Fig. 4

Simulation results on predicted particle trajectories in the SSAW field for (a-b) bead washing and (c-d) WBC washing. The green and red trajectories represent 9.77 μm and 0.87 μm beads in (a-b) and WBCs and debris in (c-d).

Fig. 5

(a-b) Stacked images showing the outlet region during our WBC washing experiment when the SSAW was off and on. (c-d) Flow cytometry results of our WBC samples before and after cell washing. Before cell washing, a considerable amount of debris (22.6%) existed in the lysed blood sample, characterized by smaller forward scatter and side scatter. After cell washing, the percentage of debris decreased to 2.16% and we collected WBCs with more than 97% purity.