LASER TRAPPING IN CELL BIOLOGY

Optical traps offer the promise of being used as noninvasive micromanipulators for biological objects. We have developed an analytical model that accurately describes the forces exerted on dielectric microspheres while in a single-beam gradient force optical trap. The model can be extended to the trapping of biological objects. The model predicts the existence of a stable trapping point and an effective trapping range. A minimum trapping power of approximately 5 mW and an effective trapping range of 2.4-mu-m have been measured for 10-mu-m diameter dielectric microspheres, and are in reasonable agreement with expected results. In cell biology, we have used the optical trap to alter the movement of chromosomes within mitotic cells in vitro and to hold motile sperm cells. Results for the mitotic cells indicate that chromosome movement was initiated in the direction opposite to that of the applied force. Chromosome velocities as high as 48-mu-m/min were observed, and are 24 times faster than normal during cell division. In sperm trapping experiments, mean sperm velocities were unchanged following short (< 30 s) exposures in the trap, while longer exposures resulted in a decrease in mean sperm velocities. Given its noninvasive nature, optical traps should prove to be useful tools in the study of biological processes.