Acoustofluidic separation of bacteria from platelets using tilted-angle standing surface acoustic wave

Abstract

Separation of microscale objects, such as cells and bacteria, is an essential sample preparation step in various microfluidic applications in microbiology, chemistry, biology, and biomedicine. Microfluidic separation of bacteria from blood cells is highly in demand to prevent or investigate bacterial infectious diseases. Unlike red and white blood cells, platelets have a similar size distribution to that of bacteria, which makes bacteria separation from platelets technically challenging. Most previous techniques for microfluidic separation rely on size as a separation marker. These size-based separation methods are not applicable to separation of the same or similarsized samples. Here, we propose an acoustofluidic method using tilted-angle standing surface acoustic wave (taSSAW) for label-free separation of the microscale objects of the same or similar size based on compressibility. From the experimental investigation with polymethylmethacrylate, polystyrene, and polycaprolactone microparticles of the same size, we found that less compressible objects migrated further when exposed to the taSSAW field formed within a microchannel. Based on the findings, we demonstrated that Escherichia coli (E. coli) can be separated from platelets because the taSSAW-induced acoustic radiation force acting on comparatively less compressible E. coli was greater than that applied to the platelets. Fluorescence microscopy, scanning electron microscope, hemocytometry, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and polymerase chain reaction were conducted to confirm the successful positive separation of bacteria from platelets with high purity of exceeding 96 % and recovery rate of exceeding 81 %.