Optical Tweezers and Traps

One of the big problems in single-molecule experiments is how to keep the molecule in place long enough to make observations on it, as well as how to grab hold of different parts of the molecule in order to manipulate it. In AFM and similar techniques the molecules are immobilized by being adsorbed on or attached to macroscopic surfaces. Another method relies on the properties of finely focused laser beams to act as optic il twcezersor optical trap-s to manipulate microscopic particles suspended in solution. 

In this way the position of small particles can be manipulated with high precision over very small distances. 

This effect can be used to position and manipulate single cells or large viruses in solution. For other biophysical studies, individual macromolecules can be tethered to one or more latex or plastic beads and manipulated using optical tweezers. Other techniques combine similar approaches using small magnetic beads. 

These stjris of optical iweezer lechmques are also used lo trap clouds ol aloms in vapours, lo slow down Iheir moiion olleclively to cool them to ve y lo .v temperatures until they beym to exhibit Bosi Einstein condensation and other bizane quantum ellecis. 

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Optical and magnetic tweezers manipulate a handle in the form of a bead attached to the end of a molecule such as DNA. Optical tweezers and traps exploit the restoring force that can be exerted on a dielectric microbead by the electric-field gradients at the focus of a laser beam. In the case of magnetic tweezers, a magnetic bead is manipulated between magnetic poles. 

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