Optical Torque Wrench,
i.e. optical torque on birefringent nano-fabricated particles
An optical tweezer (OT) is a tool which uses a focused laser to trap, manipulate and probe objects in the scale of the micrometer. Developed by physicists, it found immediately applications in studying bio-systems, as it allows (among other things) to manipulate single molecules of DNA, RNA, proteins and other nano-objects. This further jump of scale (from micro to nano) is possible due to the high sensitivity of OT and to the ability of biologists to tether bio-molecules to the microscopic object which can be trapped by OT.
Usually OTs can only apply a force to the trapped object, therefore a tension to the tethered molecule. This already allowed many important advances in understanding how DNA and proteins behave in controlled physical conditions. But it is not enough. Within the cell, the torque stored and propagated along double stranded bio-polymers (DNA, RNA) have a fundamental role, which cannot be studied in conventional OTs.
In the Dekker lab, I developped a new type of OT that can apply (and measure) also torque on special nanofabricated birefringent objects. This technique has been developed for the first time by A. La Porta and M.Wang (PRL 92 190801, 2004). The picture above shows an artistic view (I made with Blender) of the nano-fabricated birefringent cylinder, trapped in the optical trap. The polarization of the laser (arrow) aligns the extraordinary axis of the particle. A single molecule of DNA, tethered to the particle, is stretched and twisted controlling the position and angle of the cylinder via the laser. The torque can be measured analyzing the modification of the polarization as it passes through the birefringent object.
Usually OTs can only apply a force to the trapped object, therefore a tension to the tethered molecule. This already allowed many important advances in understanding how DNA and proteins behave in controlled physical conditions. But it is not enough. Within the cell, the torque stored and propagated along double stranded bio-polymers (DNA, RNA) have a fundamental role, which cannot be studied in conventional OTs.
In the Dekker lab, I developped a new type of OT that can apply (and measure) also torque on special nanofabricated birefringent objects. This technique has been developed for the first time by A. La Porta and M.Wang (PRL 92 190801, 2004). The picture above shows an artistic view (I made with Blender) of the nano-fabricated birefringent cylinder, trapped in the optical trap. The polarization of the laser (arrow) aligns the extraordinary axis of the particle. A single molecule of DNA, tethered to the particle, is stretched and twisted controlling the position and angle of the cylinder via the laser. The torque can be measured analyzing the modification of the polarization as it passes through the birefringent object.
More on the Optical Torque Wrench here.