Laser Tweezers
The discovery of optical trapping and laser tweezers in the 1980s offers an unprecedented opportunity to study chemical and biochemical processes at the single molecular level. Click here for the mechanism of laser trapping. Unlike bulk assays where ensemble information is obtained, single molecule experiments can reveal the property of sub-groups in a population and the energetic sub-trajectories in a transition process. Laser tweezers have another unique capability to measure or apply forces from femto- to pico-Newtons. These forces are in the same range of those generated by most protein motors, or needed to alter the rate or fate of most biochemical reactions. As a result, biological systems and processes have been studied using laser tweezers. There is a lag of application in chemistry, however. This is attributed to the following reasons. First, tiny amount of the material contained inside a trapped object prevents the use of many traditional detection methods, such as UV-vis and IR. Second, to build a strong optical trap, objectives with short working distance are often used. This leaves little accessible space to incorporate other detection methods. Our lab uses unique capabilities of the laser tweezers, i.e., force detection in the range of picoNewtons and spatial measurement down to Angstroms, to follow chemical and biochemical interactions such as binding events between receptors and ligands. Shown below is a setup for mechanical stretching of a single DNA molecule using laser tweezers. Click here for a study of transcription by RNA polymerase.
