(432b) Detection of 3D Position and Orientation of Microparticles Using Holographic Microscopy and Image Moment Techniques

The ability to resolve three-dimensional (3D) particle position and orientation information in real time is essential to study physical systems such as particulate suspensions and micro-swimmers. Traditionally, methods such as volumetric reconstruction via brightfield microscopy or confocal microscopy are limited to the time required for the volume scan, which results in poor performance in resolving dynamic systems. Holographic imaging techniques allow off-line reconstruction from the recorded hologram, which provides an advantageous solution to analyze such type of systems.

In this work, we developed an imaging method based on single beam in-line digital holographic microscopy (DHM). This methodology utilizes the image moment information to provide a quick, direct measurement of the center of mass and the in-plane/out-of-plane orientations of a non-spherical microparticle in 3-D space. We verified the results are in good agreement with measurements of static images of ellipsoidal particles from brightfield microscopy. We further demonstrate its application in analyzing the migration and orientation trajectory of spheroidal microparticles in a viscoelastic fluid. We also demonstrate the ability of the method to resolve the swimming trajectories of E.Coli cells within an aqueous medium. We further comment on the possible applications of this methodology in various research fields such as suspension rheology, microrheology and microbiology.