Scientists have carried out the first large scale, high-resolution recording of human sperm using a new 3D imaging technique. By accurately tracking sperm head movements they discovered that sperm sometimes swim in helices, a movement only previously hinted at by conventional imaging techniques.
Professor Aydogan Ozcan, a bioengineer from the University of California, Los Angeles (UCLA), who led the study said: 'Our intention was to create something not bounded by conventional optics. This is the first observation of something that was entirely hidden'.
The scientists tracked over 1,500 sperm per recording and looked at over 24,000 individual sperm through samples obtained from sperm banks. They found over 90 percent of sperm move along slightly curved paths with slight wiggling of the head from side to side. Roughly four to five percent swim in helices. Most sperm swim in this unusual fashion for only a short period before switching back to the more regular pattern, but what causes sperm to alter their swimming is still unclear.
By using a light-sensing chip the scientists were able to track the movement of sperm more precisely than before. They shone a red light emitting diode (LED) on the head of the sperm and a second blue LED from a different angle. The shadows cast by the two LEDs changed direction with each movement of the sperm head, allowing the scientists to track the way each individual sperm moved by creating a holographic image.
Scientists hope this imaging method could one day lead to cheaper and more portable ways for fertility researchers to look at sperm movement. 'I’ve been trying to find a way to look at sperm - moving sperm - and this seems like it would be a good method', Professor David Clapham of Boston's Children Hospital, who was not involved in the study, told Nature News.
The imaging technique may also be useful for studying single-cell swimming organisms called protozoa, which cause disease in drinking water.
Dr Leon Esterowitz, a National Science Foundation officer who oversaw funding for the UCLA study said: 'The holographic technique could accelerate drug discovery and prove valuable for monitoring pharmaceutical treatments of dangerous microbial diseases'.
The study was published in Proceedings of the National Academy of Sciences.