Focused traveling surface acoustic wave-based acoustofluidic chip for label-free cell sorting

Label-free and effective sorting of red and white blood cells based on their physical properties is crucial for subsequent single-cell analysis or immune cell engineering applications. However, cell sorting relying on the physical effects of one single physical property remains highly challenging. This paper proposes a cell sorting method based on a focused traveling surface acoustic wave (FTSAW)-based acoustofluidic chip, which leverages the ability of FTSAW acoustofluidics to comprehensively respond to multiple physical characteristics of cells (e.g., size, density, morphology, and deformability), and furthermore allows for precise setting of the action area range and adjustment of the action intensity. In experiments, a pair of focused interdigital transducers (FIDTs, characteristic frequency: 128.6 MHz) on the substrate of lithium niobate and a typical microchannel structure (single-side sheath flow focusing followed by bifurcated sorting, i.e., "two streams merging into one and then splitting into two") were designed and fabricated. Parameter optimization experiments for separation and sorting were conducted on 3 μm and 5 μm polystyrene (PS) beads, as well as red and white blood cell samples after sheath flow focusing. The results indicate that the FTSAW-based acoustofluidic chip enabled white blood cell sorting with high purity (∼90%) and high biological viability (∼98%). This study demonstrates the potential of the FTSAW-based acoustofluidic chip for cell sorting. Owing to its easy integration and advantages (non-contact operation, no sieve pore clogging, broad compatibility with cell culture media), it is expected to serve as a key pre-processing technology in microfluidic systems for single-cell analysis or cell engineering.