How Optical Tweezers allow the Study of Smaller Biological Structures

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Optical tweezers are complex combinations of lasers, microscopes, and optical/electrical equipment. These devices actually use the changes in momentum that occur when light is bent by an object. The light changes momentum and the object changes momentum in an equal and opposite fashion. If laser light can be exactingly applied, bent in exact fashion, and hit objects in a certain way, then the resulting changes in momentum can be used to move, control or herd objects around.

Stanford University has a simple summary of how optical tweezers do their work:

"Optical Tweezers use light to manipulate microscopic objects as small as a single atom. The radiation pressure from a focused laser beam is able to trap small particles." 

This is called an "optical trap".

"A beam is focused by a high-quality microscope objective to a spot in the specimen plane. This spot creates an "optical trap," which is able to hold a small particle at its center. The forces felt by this particle consist of the light scattering and gradient forces due to the interaction of the particle with the light."

Because of this physical principle, it is now possible to use finely tuned laser lights and complex systems to create traps and "force fields" that can be used to manipulate and work with biological material.

It is an extremely small world where optical tweezers work. The target objects are viruses, bacteria, living cells, organelles, small metal particles, and even strands of DNA. When used on biological structures, optical tweezers are used to apply forces in the pN-range and to measure displacements in the nm range. The objects range from 10 nano meters  to about 100 millimeters in size.

The light momentum allows the scientist to move the object and to measure the amount of movement. If the item is torqued, the amount of torque can be measured. In this way, the elasticity of DNA has been measured.

In other applications, cells can be sorted, organized, measured, manipulated and even listened to.

According to Biophotonics, Researchers have been able to observe and measure the movement motor proteins as they move along actin filaments. One scientist in Ireland worked on a protein that is exported by a bacterium and infects tobacco plants. Another group in London observed the movement of motor proteins along actin filaments.

Scientists have studied protein and how it binds to DNA or RNA. The very complex structure of folding RNA molecules has been studied by exerting force on the RNA molecule. Recently, scientists achieved the simultaneous manipulation of two single DNA molecules.

Now, optical tweezers system are capable of being commercially produced and made more widely available with measurement routines that can be used by more life sciences researchers. These are still research systems, but who knows whether some biomedical, bioindustrial agricultural or environmental optical tweezers applications and systems will come from the research?

And what is the latest research using optical tweezers? 

According to The Scientist, one of the latest optical tweezers breakthrough came when researchers at LMU Munich in Germany used an optical trap to create a "nano ear". The Nano ear can hear sounds as low as -60 decibels, or has hearing that is one million times more sensitive than the human ear. The "nano ear" uses a trapped, levitating gold particle that is super sensitive to sound waves produced by nearby or surrounding nano particles. As a result, if a bacteria "burps", the nano ear can hear it!

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