The team, led by Aydogan Ozcan, associate professor of electrical engineering and bioengineering, developed a novel lensless computational imaging platform that accurately tracked more than 24,000 individual sperm cells in a large volume. This involved observing the individual rotations of each sperm cell, including helical movement patterns, rotation speed, and linear and curved distances traveled.
Observing human sperm cells has generally been limited to conventional lens-based optical microscopes. The small size of a sperm head (about 3 to 4 micrometers), requires a high-magnification lens to observe its motion, and sperm cells’ relatively fast speed (about 20 to 100 micrometers per second) make it difficult to track them over time as they move in three dimensions, into and out of the microscope’s small observation field.
To address these challenges, the UCLA team developed a computational lens-free, on-chip imaging platform that uses the holographic shadows of sperm cells. Lens-free images of the sperm cells were acquired simultaneously using two different wavelengths of light, one red and one blue. These two light sources were set 45 degrees apart from one another, creating separate shadows at each color of illumination.
The team found that about 4 to 5 percent of the sperm cells within the sample moved in a very tight helical, or corkscrew, motion. Such movement patterns had a helix radius of about 0.5 to 3.0 micrometers, a helical rotation speed of three to 20 rotations per second, and a linear speed of 20 to 100 micrometers per second.
The research is published online in the peer-reviewed journal Proceedings of the National Academy of Sciences.
“Our results demonstrate the unique capabilities of this high-throughput, on-chip computational imaging platform by resolving the tight and rapidly evolving, rare helical trajectories of motile human sperms, as well as by revealing their statistical behavior,” Ozcan said. “This powerful lens-free imaging platform can also provide a high-throughput tool to rapidly quantify the impact of, for example, various stimuli, chemicals and drugs on the 3-D swimming patterns of sperms.”
The research was supported by a Presidential Early Career Award for Scientists and Engineers, an Army Research Office Young Investigator Award, a National Science Foundation CAREER Award, an Office of Naval Research Young Investigator Award, and the National Institutes of Health.
The UCLA Henry Samueli School of Engineering and Applied Science, established in 1945, offers 28 academic and professional degree programs and has an enrollment of more than 5,000 students. The school’s distinguished faculty are leading research to address many of the critical challenges of the 21st century, including renewable energy, clean water, health care, wireless sensing and networking, and cybersecurity. Ranked among the top 10 engineering schools at public universities nationwide, the school is home to nine multimillion-dollar interdisciplinary research centers in wireless sensor systems, wireless health, nanoelectronics, nanomedicine, renewable energy, customized computing, the smart grid, and the Internet, all funded by federal and private agencies and individual donors.