MicroBubble activated acoustic cell sorting

Abstract

Acoustophoresis, the ability to acoustically manipulate particles and cells inside a microfluidic channel, is a critical enabling technology for cell-sorting applications. However, one of the major impediments for routine use of acoustophoresis at clinical laboratory has been the reliance on the inherent physical properties of cells for separation. Here, we present a microfluidic-based microBubble-Activated Acoustic Cell Sorting (BAACS) method that rely on the specific binding of target cells to microbubbles conjugated with specific antibodies on their surface for continuous cell separation using ultrasonic standing wave. In acoustophoresis, cells being positive acoustic contrast particles migrate to pressure nodes. On the contrary, air-filled polymer-shelled microbubbles being strong negative acoustic contrast particles migrate to pressure antinodes and can be used to selectively migrate target cells. As a proof of principle, we demonstrate the separation of cancer cell line in a suspension with better than 75% efficiency. Moreover, 100% of the microbubble-cell conjugates migrated to the anti-node. Hence a better upstream affinity-capture has the potential to provide higher sorting efficiency. The BAACS technique expands the acoustic cell manipulation possibilities and offers cell-sorting solutions suited for applications at point of care.

Keywords: Acoustophoresis; Cell sorting; Contrast agent; Microbubble; Microfluidic separation.

Fig. 1

Schematic illustration of the microbubble-activated acoustic cell sorting (BAACS) using immunoaffinity cell capture with antibody-coated MBs. Target cells, affinity conjugated to MBs, migrate towards the antinode while none-target cells migrate towards the nodes and can be separated

Fig. 2

Trapping of polystyrene particles and MB at stationary and flow-through conditions. a Bright field (left) and fluorescent image (right) of streptavidin coated rhodamine labeled MB (red) trapping at antinodes (0, λ, λ/2) mostly at middle antinode and polystryrene particles (green) trapping at nodes (λ/4, 3λ/4),in standing waves at 140 kPa. b The bright field (right) and fluorescent image (left) of MBs flowing in standing waves through antinodes at the center

Fig. 3

Cell–MBs binding. a Bright field and b fluorescent image where the MBs are labeled red and the cancer cell lines green

Fig. 4

Acoustic based sorting in stationary condition. a The MBs-cell complex are at antinodes under acoustic field, and b the mixture of cells (green) and MBs-cell complex (red-green) where cells are at nodes and MBs-cell complex at antinodes

Fig. 5

MBs assisted cell sorting in flow condition. a Merged image of frames shows the MBs (red streaks) and Mb-cell complex (red-green overlapping streaks) flowing through the centre of the capillary via antinodes under acoustics and cells (as green streaks) passing through nodes. b The fluorescent intensity peaks representing lateral distribution of MB (red), cells (green) and MB-cell complex (red-green overlap) at nodes and antinodes. c Sorting efficiency of 75% of MBs-cell complex at flow rate of 180 μl/min. 100% of the MBs go to antinode