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Laser tweezers use laser beams to trap microscopic particles with precise three-dimensional positioning, exploiting a phenomenon called refractive index mismatch. They only work with dielectric materials and can be used to levitate bacteria, viruses, atoms, and molecules. Laser tweezers have been invaluable in studying biological machines and contribute to the emerging science of nanotechnology. Steven Chu won the 1997 Nobel Prize in Physics for his work on laser tweezers.
Laser tweezers, also known as optical tweezers, use laser beams to trap microscopic or nanoscopic particles with precise three-dimensional positioning. Laser beams exploit a phenomenon called refractive index mismatch. We see this every time we look at a straw in a glass of water. On tiny scales, the particle’s subtle bending of light causes a momentum to be transmitted to it, projecting a tiny attractive or repulsive force. The result is extremely fine precision and control over a single particle in the beam, control on sub-nanometer scales.
Laser tweezers only work when the material used is dielectric, i.e. an insulator against electromagnetic fields. A laser focused in the tweezers generates an electromagnetic field in the form of condensed light. The laser approach can be used to levitate bacteria, viruses, and even individual atoms and molecules. For many applications, small samples are attached to a slightly larger bead. Multiple laser tweezers can also be used to pull on parts of a molecule, stretching it and allowing scientists to watch as it retracts. This is incredibly useful for elucidating their subtle chemical properties.
The phenomenon of optical scattering by microscopic particles was first reported by Bell Labs scientist Arthur Ashkin in 1970. Then, in 1986, scientist Steven Chu and others wrote a paper on the subject and greatly improved i systems. Dr. Chu went on to apply laser tweezers in a wide variety of useful areas, including cooling atoms by holding them in place, and won the 1997 Nobel Prize in Physics for his hard work.
Laser tweezers have been invaluable in studying the tiny features of biological machines, such as the ubiquitous biological motors that drive movement in the cell. This contributes to the emerging science of nanotechnology and greatly expands our understanding of biology. Laser tweezer-based probing of the cytoskeleton of cells helped scientists create a high-resolution map of the cell, with more detail than other approaches could have produced. Laser tweezers continue to be a hot area of research, with intrepid teams at Berkeley, Stanford, MIT and many other universities tapping into the investigative possibilities the technology has to offer.
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