Optical Tweezers, Optical Torque Wrench
Optical tweezers can trap microscopic particles exerting linear forces on them. Using birefringent nano-fabricated particles shaped as cylinders, optical tweezers can be expanded with torque manipulation and detection. Forces of the order of the 0.1-10 pN and torque of the order of 1-1000 pN nm can be applied and measured.
The magnetic field of permanent magnets is used to apply force and torque on super-paramagnetic microscopic beads. In this way single biopolymers like DNA and RNA tethered to the bead, can be stretched and twisted, while their extention and conformation is monitored by optical tracking microscopy.