Four-dimensional motility tracking of biological cells by digital holographic microscopy.

Three-dimensional profiling and tracking by digital holography microscopy (DHM) provide label-free and quantitative analysis of the characteristics and dynamic processes of objects, since DHM can record real-time data for microscale objects and produce a single hologram containing all the information about their three-dimensional structures. Here, we have utilized DHM to visualize suspended microspheres and microfibers in three dimensions, and record the four-dimensional trajectories of free-swimming cells in the absence of mechanical focus adjustment. The displacement of microfibers due to interactions with cells in three spatial dimensions has been measured as a function of time at subsecond and micrometer levels in a direct and straightforward manner. It has thus been shown that DHM is a highly efficient and versatile means for quantitative tracking and analysis of cell motility.