Abstract
Optical traps offer the promise of being used as noninvasive micromanipulators for biological objects. An analytical model was developed 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 effective trapping range. A minimum trapping power of approximately 5 mW and an effective trapping range of 2.4 mu m were measured for 10- mu m-diameter dielectric microspheres and are in reasonable agreement with expected results. In cell biology, the optical trap was used 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.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Highlights
IT is possible to use light, in the form of an optical trap, to manipulate microscopic objects without physical contact
While the single beam gradient force trap for atoms was proposed [2], it was not until recently that this technique was applied to the optical trapping of microspheres [3]
A model has been developed which quantifies, for the first time, the forces acting on dielectric microspheres in a single-beam gradient force optical trap
Summary
IT is possible to use light, in the form of an optical trap, to manipulate microscopic objects without physical contact. Various biological objects, including viruses, bacteria, yeast cells, and red blood cells have been trapped successfully, using both argon and Nd :YAG lasers in the single-beam configuration. One experiment measured the minimum power required to trap the microsphere, while a second experiment determined the range over which a microsphere, initially caught in the trap, could be recovered Results from both experiments corroborate the model presented . One set of experiments evaluated the effect of the single-beam optical trap on the velocity of motile spermatozoa [ l l ] Another set of experiments employed the optical trap to study chromosome movement during the process of cell division [121.
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