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Phys Rev Lett. 2006 Aug 4;97(5):058301. Epub 2006 Aug 1.

Direct measurement of torque in an optical trap and its application to double-strand DNA.

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  • 1Institute of Biophysics, Biological Research Center, Hungarian Academy of Sciences, 6726 Szeged, Hungary.


We present a method that offers the possibility to directly apply and measure torque on particles in an optical trap. It can be used to rotationally manipulate biopolymers attached to appropriate particles. A flat object is trapped and oriented in the focus of a linearly polarized laser light. The direction and power of the orientational trap are controlled by the polarization state of the light. As a demonstration of the capabilities of the method, we examined the torsional stiffness of dsDNA (lambda-DNA) in its linear torsional regime by directly measuring the torque generated by the molecule.

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