Abstract
Sperm motility is an important concept in fertility research. To this end, single spot laser tweezers have been used to quantitatively analyze the motility of individual sperm. However, this method is limited with throughput (single sperm per spot), lacks the ability of in-situ sorting based on motility and chemotaxis, requires high laser power (hundreds of milliWatts) and can not be used to dynamically monitor changes in sperm swimming behavior under the influence of a laser beam. Here, we report a continuous 3-D ring-shaped laser trap which could be used for multi-level and high-throughput (tens to hundred sperm per ring) sperm sorting based on their motility and chemotaxis. Under a laser power of only tens of milliWatts, human sperm with low to medium velocity are slowed down, stopped, or forced to change their trajectories to swim along the ring due to the optical gradient force in the radial direction. This is the first demonstration of parallel sperm sorting based on motility with optical trapping technology. In addition, by making the sperm swimming along the circumference of the ring, the effect of laser radiation, optical force and external obstacles on sperm energetics are investigated in a more gentle and quantitative way. The application of this method could be extended to motility and bio-tropism studies of other self-propelled cells, such as algae and bacteria.
Highlights
Artificial insemination (AI) has been of great practical importance in animal husbandry and in the effort to preserve endangered species
Noninvasive and high throughput analysis of sperm motility is crucial for successful artificial insemination and genetic improvement programs
The thin chambers (30 Ī¼m) used in computer aided sperm analysis (CASA) may affect the behavior of sperm that swim with large transverse amplitudes (Baumber and Meyers, 2006), and the errors encountered by CASA when dealing with phase contrast images often lead to errors in the actual sperm number detected in the field
Summary
Artificial insemination (AI) has been of great practical importance in animal husbandry and in the effort to preserve endangered species. The overall quality of the sperm to be used is among the most critical factors in an effective AI program, which makes sperm assessment an essential procedure before cryopreservation. Noninvasive and high throughput analysis of sperm motility is crucial for successful artificial insemination and genetic improvement programs. Conventional technologies use a microscope to evaluate one sperm at a time subjectively and qualitatively, which is labor intensive and lacks a universal standard. These considerations give rise to a strong need for an automated, quantitative, and objective assessment tool for sperm quality. In the last 25 years, computer aided sperm analysis (CASA) has been developed to offer objective assessment of sperm motility for large populations.
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