3D tracking of the head and flagellar motion of sex-sorted bovine sperm using on-chip holography (Conference Presentation)

The differences in the swimming behavior of sperm cell populations that carry the opposite sex chromosome have been an important topic of research, aiming to shed more light on the seemingly random process of gender determination at conception. Earlier studies on human sperm cells resulted in a misconception that, Y-chromosome bearing sperm cells swim faster than X-chromosome bearing sperm cells as they carry a lighter payload. This has been clarified with more recent studies using modern computer-aided semen analysis (CASA) systems and improved sex-sorting techniques, showing that the velocity parameters of the two sperm populations exhibit similar values. CASA systems typically rely on conventional optical microscopes however, where the trade-off between spatial resolution and field-of-view and poor depth resolution necessitate confining the sperm cells into shallow chambers which limit their 3D motion. Alternatively, dual-view on-chip holographic imaging offers a unique capability to image free-swimming sperm cells across a large volume (~1.8 μl) and depth (~0.6 mm) in 3D. Operating our platform at 300 fps, we have comparatively analyzed the complete 3D motion characteristics of 235 X-sorted and 289 Y-sorted free-swimming bovine sperm cells, which include the head translation and spin as well as the 3D flagellar beating. While there was no significant difference in the velocity parameters, it was observed that the Y-sorted sperm had a stronger preference for helical trajectories compared to X-sorted sperm with a higher linearity. Comparatively studying the kinematic responses to the surrounding chemicals and ions could help better understand the reasons behind these observed differences.