First discovered in the 1970s by Arthur Ashkin at Bell Laboratories and further developed by physicists and biologists worldwide in the 1980s and 1990s (many of whom went on to win Nobel Prizes based on their work), optical trapping has become a well-respected research tool for single-molecule and force-measurement studies (see "How optical trapping works").1 In recent years, its unique ability to measure the position of a specimen or particle while a force is being exerted on it-combined with the push to study cellular and molecular processes at increasingly precise scales-has prompted new interest in optical trapping, particularly for biophysics and materials-science applications.
"It has become possible to use a number of techniques-FRET, trapping, fluorescence, atomic-force microscopy, and magnetic tweezers, for instance-to isolate and study one molecule or nucleic acid at a time," said Steven Block, professor of applied physics and biological sciences at Stanford University (Stanford, CA) and a pioneer in the field of optical trapping. "Optical tweezers have the advantage of being able to apply controlled forces and controlled torques to biological elements."
Last February, for example, Block's group used infrared light to trap and map the motion of RNA polymerase at 1 Å resolution, an important advance in the study of protein mechanics (see Fig. 1).2 These experiments utilized a custom-built optical-trapping system with a diode-pumped solid-state laser (532 or 1064 nm) housed in a separate sound-proof room from the power supply, which eliminates the need for cooling and vibration control, resulting in a very stable beam-paramount when trying to measure atoms, Block notes.
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