High-Speed Magnetic Tweezers for Single-Molecule Manipulation

Single-molecule force spectroscopy (SMFS) allows for the direct study of biological mechanisms such as protein dynamics and enzymatic activity by applying a force to a biomolecule of interest and studying the resulting effects. Thus, SMFS can unlock key insights into energy landscapes and fundamental biological processes. One common force spectroscopy instrument designed to manipulate single-molecules such as proteins and nucleic acids are magnetic tweezers (MTs).

MTs apply a magnetic field on microscopic magnetic beads to induce a force on a collection of biomolecules. This magnetic field can be produced by either a set of permanent magnets or an electromagnetic. In this configuration, we utilize a custom-made permanent magnet configuration designed to maximize the applied force. One main feature of MTs is the ability to rotationally manipulate biomolecules, as the intrinsic magnetic dipole of the magnetic beads allows for torque measurements to be made by rotating the magnetic field applied to these beads. This rotational ability can be used to measure properties such as torsional stiffness.

Traditionally, we have used optical tweezers (OT) and atomic force microscopy (AFM) to manipulate biomolecules. However, the rotational and constant-force capabilities of MTs make them a complementary addition to our current array of single-molecule techniques. While MTs are valuable for manipulation of single-molecules, they suffer from low spatial and temporal resolution compared to AFM and OT. This is because the tracking of a magnetic bead is done utilizing images of the bead at ~60Hz, however, this is often much longer than the characteristic time-scale of many biomolecules processes.

In this work, we implement various techniques to improve these resolutions and achieve a high-speed MT design. We use a high-speed complementary metal–oxide–semiconductor (CMOS) camera capable of capturing images at greater than 2000 frames per second in combination with GPU accelerated image processing. The accuracy of this design will then be analyzed by measuring a force calibration standard such as the elasticity of double stranded DNA.