A human sperm encounters an egg, seen via electron microscope.
For the first time, scientists have successfully plotted the paths of sperm in 3-D, revealing corkscrew-like trajectories and "hyperactive" swimmers.
Based on a sensor chip not unlike those in smartphones and digital cameras, the new technology could lead to better male fertility testing and insights into the behaviour of other microorganisms, researchers say.
Tiny and fast - even for microorganisms - human sperm are notoriously difficult to study. Nevertheless the team trained their tool on the male reproductive cells rather than easier quarry. Why? Because "sperm is one of the most important microorganisms in life," study leader Aydogan Ozcan said.
Sperm movements are notoriously hard to catch on camera. Source: Nature.
Ozcan and his team began by placing the sperm - obtained from a sperm bank - on a silicon sensor chip.
The researchers shone red and blue LED lights from different directions on the moving sperm - 24,000 cells over the course of the study. Each sperm cast two different, and different coloured, shadows, which the chip recorded. Later a computer program combined the two sets of data to reconstruct the cells' meandering paths.
At any given time, conventional optical microscopes "can only observe a very limited number of sperms" in three dimensions, said Ozcan, an electrical engineer at the University of California, Los Angeles, via email. But with the new sensor technique, "we can easily track more than 1,500 sperms in 3-D within a single experiment."
"Hyperactive" Sperm
All that data revealed distinctly different swimming modes for sperm. The vast majority of the sperm followed a "typical" path - more or less a straight line.
But some swam in a helical, or corkscrew, pattern previously only hinted at by fuzzy microscope results. Other sperm were labelled "hyperactive" due to their jerky direction changes, which sometimes sent them careening in reverse.
Video: Sperm Charted Swimming in Corkscrew Pattern
According to Ozcan, a former National Geographic emerging explorer, there's currently no known relationship between the health of a sperm and its swimming style, but the new imaging technique could open the door for such studies in the future.
In fact, he said, the sensor system may yet shed a bit of red and blue light on the movements of other microorganisms and on the effects of drugs and chemicals - caffeine, for example - on sperm quality.
Not to mention potentially offering men a sharper sense as to whether, in Seinfeldian parlance, their "boys" can swim. "It is possible," Ozcan said, "that this technique or a variation of it could be used for screening or quantification of sperm."
The 3-D sperm study is published in this week's issue of the journal Proceedings of the National Academy of Sciences.
Top image: Screen capture from video.
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