Magnetic Tweezers for Single-Molecule Manipulation

Magnetic tweezers provide a versatile tool enabling the application of force and torque on individual biomolecules. Magnetic tweezers are uniquely suited to the study of DNA topology and protein–DNA interactions that modify DNA topology. Perhaps due to its presumed simplicity, magnetic tweezers instrumentation has been described in less detail than comparable techniques. Here, we provide a comprehensive description and guide for the design and implementation of a magnetic tweezers instrument for single-molecule measurements of DNA topology and mechanics. We elucidate magnetic trap design, as well as microscope and illumination setup, and provide a simple LabVIEW-based real-time position tracking algorithm. In addition, we provide procedures for production of supercoilable DNA tethers, flow-cell design, and construction tips.