What Are Laser Tweezers?
Laser tweezers—one kind of optical trap—use focused laser light to grab and hold particles just millionths of a meter wide. The recent application of laser tweezers in biology has made possible the study of individual sub-cellular components. Observing optically trapped particles attached to functional molecular motors is like watching and feeling a dog on a leash walk—the working details of cellular processes are revealed. Common laser-tweezer setups involve a focused laser, a microscope, a detector, and a translation stage. (The translation stage allows the researcher to move the entire sample by nanometer distances.) When studying the interaction between two biomolecules, one molecule is often fixed to a glass surface while the other is attached to a trappable bead. The trapped bead and attached molecule are then positioned in the vicinity of the fixed molecule that latches on and goes to work. With a firm grip on the trap, the researcher goes along for the ride, observing the rate
Laser tweezers, also known as optical tweezers, use laser beams to trap microscopic or nanoscopic particles with precise 3-dimensional positioning. The laser beams take advantage of a phenomenon called refractive index mismatch. We see this whenever we look at a straw in a glass of water. On tiny scales, the subtle bending of light by the particle results in momentum being conveyed to it, projecting a tiny attractive or repulsive force. The outcome is extremely fine-grained precision and control over a single particle in the beam, control on sub-nanometer scales. The laser tweezers only work when the material used is dielectric, meaning an insulator that is averse to electromagnetic fields. A focused laser in the laser tweezers generates an electromagnetic field in the form of condensed light. The laser tweezer approach can be used to levitate bacteria, viruses, and even single atoms and molecules. For many applications, tiny samples are attached to a slightly larger microscopic bead.
