Force Generated by Human Sperm Correlated to Velocity and Determined Using a Laser Generated Optical Trap

The development of the single beam gradient force optical trap has made it possible to manipulate cells solely by laser light. A continuous wave Nd:YAG (1.06 microns) laser beam was directed into a conventional microscope and focused onto the viewing plane by the objective lens. The laser beam power at which human sperm were released from the trap was measured and correlated to the sperm's linear velocity before trapping. The mean trapping power readings for slow, medium, and fast motile sperm were 57, 73, and 84 mW, respectively. The analysis of measurements over the total population demonstrated that zig-zag motile sperm had significantly higher mean power readings when compared with straight motile sperm with similar mean linear velocities. In two cases, specimens required significantly less trapping power when the measurements were repeated 24 hours later.