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Better, Stronger, Faster: High-Throughput Sperm Sorting

Researchers at the University of California, Irvine (UCI) and San Diego (UCSD), have developed a rapid new sorting technique for sperm using a laser trap that can separate stronger, faster sperm from slower sperm. Faster sperm are more likely to successfully fertilize an egg, so the technique could improve the chances of conception via in vitro fertilization by ensuring that only the fastest, strongest sperm are used. The technique could find wide application in animal husbandry and human fertility treatments.

UCI scientist Bing Shao and her colleagues at UCSD have developed a new laser-based technique that enables not only analysis of swimming speed, but on-the-spot sorting of more desirable faster from slower sperm. Shao's team used special cone-shaped lenses called "axicons," which, when combined with a standard lens and a laser, form a ring-shaped focus (an annular laser trap). Such an arrangement has been used for laser machining as well as for trapping atoms. The trap acts as a kind of "speed bump" for swimming sperm, depending on the power of the laser used: slower, weaker sperm below the threshold of the laser power being used will be slowed down, redirected, or stopped altogether in the trap, while faster, stronger sperm are hardly affected at all because their energies are above the critical threshold. The researchers used both human sperm and gorilla sperm in their experiments, the latter as a control, since gorilla sperm are slower and weaker than human sperm.

Since X sperm generally are heavier and swim slower, while Y sperm are lighter and swim faster, it is also possible to use this new technique to separate sperm carrying
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