Two-photon microscopy of acoustofluidic trapping for highly sensitive cell analysis.

We combine two-photon-excited fluorescence microscopy and acoustofluidic trapping in a spherical microchamber to in vitro study cells and cell clusters three-dimensionally close to in vivo conditions. The two-photon microscopy provides the in-depth 3D analysis of the spherical microchamber dimensions as well as the positions of trapped samples therein with high spatial precision and high temporal resolution enabling even tracking of the fast moving particles. Furthermore, optical sectioning allows to gather information of individual cells in trapped cell clusters inside the chamber. We demonstrate real-time monitoring of osmosis in A549 lung cells and red blood cells as one possible biomedical application. The observed osmosis reduced the cell membrane diameter by approximately 4 μm in the A549 cells and by approximately 2 μm in the red blood cells. Our approach provides an important optical tool for future investigations of cell functions and cell-cell interactions avoiding wall-contact inside an acoustofluidic device.