A new technique has allowed scientists to track the movements of thousands of sperm for the first time.
Conventional optical microscopes only allow researchers to track the movements of a few sperm at a time. But the sensor that Aydogan Ozcan and his team at the University of California, Los Angeles created can track over 1,500 human sperm cells in three dimensions.
Sperm are notoriously difficult to study, because of their small size and fast speed. Sperm are quick even for the standards of microorganisms, and even those 1,500 sperm cells were swimming in a volume of liquid that was smaller than a single drop of water. But researchers were determined to study the organisms because, as Ozcan says, "Sperm is one of the most important microorganisms in life."
The team began by placing sperm on a silicon sensor, not unlike those found in smartphones and digital cameras. Then the researchers set red and blue LED lights on the sperm. The sperm cast two different-colored shadows, which they recorded. Later, they used a computer program to reconstruct the movements of the sperm cells based on the shadow movements, producing a holographic image.
They found that most sperm move in straight, linear directions. But some are what they called "hyperactive," with jerky direction changes and sometimes careening in reverse. Others swam in corkscrew, cyclical patterns, which had only been hinted at with microscope results.
There is currently no known link between sperms' swimming styles and fertility, but they believe that their sensor can open the door to research into that possibility. The team also believes that the sensors could pave the way into establishing the effect that certain food and drugs, like caffeine, can have on sperm mobility and health. The technique, they say, can also be used to screen or quantify the number of sperm that men have.
Their work was published in the Proceedings of the National Academy of Sciences. A video of sperms' movement can be found below.