An optical apparatus for rotation and trapping.

Area of Science:

• Biophysics
• Optical physics
• Nanotechnology

Background:

• Optical tweezers are crucial for manipulating microscopic objects.
• Existing optical tweezers often lack precise torque control.
• Studying biomolecular mechanics requires simultaneous force and torque application.

Purpose of the Study:

• To design and test a novel single-beam optical tweezers apparatus for measuring and exerting torque and force.
• To enable high-bandwidth, continuous rotation studies of optically anisotropic microparticles.
• To demonstrate the instrument's utility in studying DNA supercoiling.

Main Methods:

• Utilized an electro-optic modulator (EOM) to control laser polarization for angular orientation.
• Developed a feedback servo loop measuring transmitted light's circular components to assess and maintain torque.
• Implemented rapid polarization reversal to extend EOM's angular range for unlimited rotation.
• Employed microfabrication techniques to create suitable rotating particles.

Main Results:

• The optical torque wrench achieves simultaneous force (0.1–100 pN) and torque (1–10,000 pN nm) application.
• The system allows for high-bandwidth, continuous rotation with precise torque control.
• Demonstrated proof-of-principle by studying the supercoiling of single DNA molecules.

Conclusions:

• The developed optical torque wrench is a significant advancement for biophysical studies.
• The instrument provides unprecedented control for investigating the mechanical properties of biomolecules.
• This technology opens new avenues for understanding molecular mechanisms in biological systems.