Acousto-optofluidic 3D single cell imaging of macrophage phagocytosis of Pseudomonas Aeruginosa

Understanding how immune cells such as monocytes or macrophages within our blood and tissue engulf and destroy foreign organisms is important for developing new therapies. The process undertaken by these cells, called phagocytosis, has yet to be observed in real-time at the single cell level. Microfluidic-based imaging platforms offer a wide range of tools for precise fluid control and biomolecule manipulation that makes regulating long term experiments and data collection possible. With the compatibility between acoustofluidics and light-sheet fluorescent microscopy (LSFM) previously demonstrated, here an acousto-optfluidic device with on-chip fluid flow direction control was developed. The standing surface acoustic waves (SSAWs) were used to trap, load and safeguard individual cells within a highly controllable fluid loop, created via the triggering of on-chip PDMS valves, to demonstrate multiple rounds of live single cell imaging. The valves allowed for the direction of the fluid flow to be changed (between forward and reverse operation) without altering the inlet flow rate, an important factor for performing reproducible and comparable imaging of samples over time. With this high-resolution imaging system, volumetric reconstructions of phagocytosed bacteria within macrophages could be resolved over a total of 9 rounds of imaging: totalling 19 reconstructed images of the cell membrane with visible intracellular bacteria.